Activation of the Redox-regulated Chaperone Hsp33 by Domain Unfolding

Abstract

The molecular chaperone Hsp33 in Escherichia coli responds to oxidative stress conditions with the rapid activation of its chaperone function. On its activation pathway, Hsp33 progresses through three major conformations, starting as a reduced, zinc-bound inactive monomer, proceeding through an oxidized zinc-free monomer, and ending as a fully active oxidized dimer. While it is known that Hsp33 senses oxidative stress through its C-terminal four-cysteine zinc center, the nature of the conformational changes in Hsp33 that must take place to accommodate this activation process is largely unknown. To investigate these conformational rearrangements, we constructed constitutively monomeric Hsp33 variants as well as fragments consisting of the redox regulatory C-terminal domain of Hsp33. These proteins were studied by a combination of biochemical and NMR spectroscopic techniques. We found that in the reduced, monomeric conformation, zinc binding stabilizes the C terminus of Hsp33 in a highly compact, α-helical structure. This appears to conceal both the substrate-binding site as well as the dimerization interface. Zinc release without formation of the two native disulfide bonds causes the partial unfolding of the C terminus of Hsp33. This is sufficient to unmask the substrate-binding site, but not the dimerization interface, rendering reduced zinc-free Hsp33 partially active yet monomeric. Critical for the dimerization is disulfide bond formation, which causes the further unfolding of the C terminus of Hsp3 and allows the association of two oxidized Hsp33 monomers. This then leads to the formation of active Hsp33 dimers, which are capable of protecting cells against the severe consequences of oxidative heat stress. The molecular chaperone Hsp33 in Escherichia coli responds to oxidative stress conditions with the rapid activation of its chaperone function. On its activation pathway, Hsp33 progresses through three major conformations, starting as a reduced, zinc-bound inactive monomer, proceeding through an oxidized zinc-free monomer, and ending as a fully active oxidized dimer. While it is known that Hsp33 senses oxidative stress through its C-terminal four-cysteine zinc center, the nature of the conformational changes in Hsp33 that must take place to accommodate this activation process is largely unknown. To investigate these conformational rearrangements, we constructed constitutively monomeric Hsp33 variants as well as fragments consisting of the redox regulatory C-terminal domain of Hsp33. These proteins were studied by a combination of biochemical and NMR spectroscopic techniques. We found that in the reduced, monomeric conformation, zinc binding stabilizes the C terminus of Hsp33 in a highly compact, α-helical structure. This appears to conceal both the substrate-binding site as well as the dimerization interface. Zinc release without formation of the two native disulfide bonds causes the partial unfolding of the C terminus of Hsp33. This is sufficient to unmask the substrate-binding site, but not the dimerization interface, rendering reduced zinc-free Hsp33 partially active yet monomeric. Critical for the dimerization is disulfide bond formation, which causes the further unfolding of the C terminus of Hsp3 and allows the association of two oxidized Hsp33 monomers. This then leads to the formation of active Hsp33 dimers, which are capable of protecting cells against the severe consequences of oxidative heat stress. The molecular chaperone Hsp33 belongs to a novel class of redox-regulated proteins, whose activity is regulated by their redox state (1Paget M.S. Buttner M.J. Annu. Rev. Genet. 2003; 37: 91-121Crossref PubMed Scopus (254) Google Scholar). In prokaryotes, Hsp33 is located in the highly reducing environment of the cytosol, where it is monomeric and largely devoid of chaperone function. Upon exposure to oxidative stress in vitro or in vivo, Hsp33 is quickly activated as a potent molecular chaperone (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google Scholar). The switch that regulates the activity of Hsp33 is a novel, very high affinity zinc-binding motif (CXCX27-32CXXC) that is located in the C terminus of the protein (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). The four absolutely conserved cysteines that constitute this redox switch are kept in the reduced deprotonated thiolate anion state and together coordinate one zinc(II) ion (KD ∼ 10-18 m) (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). Under oxidative stress conditions, these four cysteines release zinc and rapidly form two intramolecular disulfide bonds, connecting the two pairs of neighboring cysteines, Cys232 with Cys234 and Cys265 with Cys268 (4Barbirz S. Jakob U. Glocker M.O. J. Biol. Chem. 2000; 275: 18759-18766Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar). Disulfide bond formation and concomitant zinc release then induces the dimerization of two oxidized Hsp33 monomers (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). Hsp33 is a highly chaperone which is to the of a of To Hsp33 for protein reducing conditions to This Hsp33 a reduced which is active but to the proteins to the for this Lilie H. Jakob U. J. PubMed Scopus Google Scholar). that Hsp33 senses through its C-terminal four-cysteine zinc center, with zinc an for the formation of the disulfide bonds and the rapid activation of the chaperone of Hsp33 (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). The changes that disulfide bond formation and the dimerization of Hsp33 largely unknown. This is in for the C terminus of Hsp33. of the that were were of which the of cysteines J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Biol. PubMed Scopus Google Scholar). PubMed Scopus Google to that Hsp33 conformational changes that Hsp33 in the oxidized conformation, but not in the reduced, inactive molecular with their proteins through these are to the substrate-binding site of Hsp33. it is that the substrate-binding site is in the reduced, inactive form but in the active the of these the activation the that oxidized Hsp33 form both monomers and were We that the C-terminal zinc-binding domain is fully in the reduced Hsp33 This appears to both the dimerization and the substrate-binding Upon zinc release and disulfide bond formation, the C-terminal domain of Hsp33 This the substrate-binding site and the dimerization interface. NMR and of the C-terminal domain and the Hsp33 protein that the C-terminal redox switch domain the of the chaperone domain appears largely by the and dimerization Hsp33 and the Hsp33 protein were in the of reducing as (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). The to the The that Hsp33 as (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google Scholar). The of the an in the Hsp33 were with this (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google and the protein and to the of Hsp33 (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google Scholar). The for of the C-terminal domain fragments of Hsp33 were and as The were a and to the of the The were and the Hsp33 fragments were native conditions, an anion by a or NMR of the C-terminal were by the cells in and with and the with and the of to a of The protein fragments were the that for the The of the protein fragments by and and as J. H. Jakob U. PubMed Scopus Google Scholar). protein are in the oxidized of Hsp33 and its variants were protein of in with a with an and were in cells and with were with the by for the of in the Hsp33 and were in and were The to and the were to and The of in the of protein as of the Hsp33 the of as with (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). in To with or without Hsp33. To the of Hsp33 the of unfolding native in in the or of Hsp33. In both a with a and The and were to and the were to To the of Hsp33 unfolding native in the or of Hsp33. and to The were to Zinc and of release of zinc Hsp33 by as (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). reduced, Hsp33 or protein with in were to the of zinc release as well as the of chaperone activity unfolding as a and NMR reduced, and fragments for Hsp33 were in and of for To reduced, in and for in were for and to the of the of the with for Hsp33 and were by or reduced, Hsp33 with for or The oxidized were then against were a in a with were and then for in Hsp33 the Hsp33 proteins were oxidized by a redox of reduced and oxidized H. U. S. PubMed Scopus Google Scholar). The and with a protein of NMR were and The Hsp33 activation of Hsp33 is a process (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). In the reduced Hsp33 disulfide bond formation and its This causes the formation of zinc-free oxidized monomeric Hsp33 In a two oxidized Hsp33 monomers to form the fully active molecular To the of zinc binding and disulfide bond formation in the activation process of and to and the and conformational changes that this we four of reduced, monomeric reduced, zinc-free monomeric oxidized monomeric and oxidized Hsp33. reduced, Hsp33 monomers as well as oxidized Hsp33 are to and in (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). To a reduced, Hsp33 we to a of in which (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). This protein to the of zinc the activity and of monomeric Hsp33 without the of disulfide bond To oxidized monomeric which is an in the activation of and we to the highly conserved dimerization in an to and are located the dimerization and are highly conserved J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). and are absolutely conserved found in Hsp33 found in but two Hsp33 where it is with a and the two bonds the of one and the of as well as the of of the J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). that the of these dimerization without the or redox activity of Hsp33. This then to Hsp33 variants that form disulfide bonds but monomeric both in vitro and in In one we the with the the In Hsp33 we both and with the both proteins both in vitro and in vivo, we the with the of Hsp33 and to The of Hsp33 to this and found to to the Hsp33 The protein then reduced and with is the with zinc and were the a of zinc to protein In disulfide bond formation induces the release of zinc (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). of the zinc release a to the of disulfide bond formation in to (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). in the of zinc release is for both Hsp33 and the and to the of disulfide bond formation in both Hsp33 and the the formation of two disulfide bonds in both proteins not This that the of a a highly conserved of Hsp33 not the of Hsp33. To the of the oxidized oxidized to oxidized Hsp33 reduced Hsp33 monomers and the constitutively monomeric Hsp33 and (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google In with the oxidized protein very to monomeric Hsp33 and with To the for dimerization of the of the oxidized the protein that in these we were to We that the of the in the of proteins must of the of oxidized which to (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). The monomeric state by in which a molecular of of the protein These that the of the highly conserved to in a constitutively monomeric Hsp33 This the oxidized monomeric Hsp33 which is the activation process of Hsp33 in The the activity of the oxidized monomeric of we the activity that to the chaperone activity of Hsp33 (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). We the of the constitutively monomeric protein the of by in high of is to to its native state rapidly which by a of oxidized Hsp33 to to the of In the of oxidized monomeric protein a the of This very to the in the of reduced Hsp33 monomers or reduced monomers not which are to largely inactive Hsp33 were as a protein of that oxidized Hsp33 monomers are to with highly proteins or that not high affinity for these to with their To these two we the activity of oxidized monomers the of unfolding that are conditions and with a in and To with this chaperone and in of the for the proteins, are This is in where a of oxidized Hsp33 to fully capable of the of the oxidized active as a chaperone in that a of monomers to as as a of oxidized Hsp33 to and In the reduced Hsp33 a the of heat which is to the of a of Hsp33 the of the were unfolding as a protein of or the of Hsp33 not These that the of Hsp33 unfolding proteins as unfolding or unfolding by the of oxidized Hsp33 monomers and not by the of Hsp33 This that a substrate-binding site, which high affinity for unfolding To against the that the of proteins as or the affinity of the chaperone must This appears to by the dimerization of two oxidized which the two substrate-binding the substrate-binding as a to the and affinity of binding is a in chaperone and well studied with the Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). This is by the of active Hsp33 dimers, which two substrate-binding both of which both Hsp33 J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Biol. PubMed Scopus Google Scholar). of of Hsp33 protein as a protein that the activation process of Hsp33 is a which is by disulfide bond formation (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). This that of the oxidized Hsp33 monomers is absolutely for Hsp33 to with highly as or which quickly we that disulfide bond formation of Hsp33 Hsp33 to a that is sufficient to the of unfolding proteins as unfolding or This to of Hsp33 that with proteins as proteins the of disulfide bond formation and in we found that this the and Hsp33 and protein were with the were and for zinc release and with or for the to the of unfolding The of Hsp33 were for both Hsp33 and proteins very to the of zinc release and both Hsp33 and with the to the that disulfide bond formation of Hsp33 is sufficient to Hsp33 a molecular chaperone that with unfolding and protein Hsp33 to against and investigate the in of Hsp33 and to Hsp33 dimerization is for we a of Hsp33 We found that the of the Hsp33 is for the high of coli cells that are constitutively to the of cells to a against oxidative stress S. Biol. PubMed Scopus Google which appears to in to the of oxidized and activated Hsp33 (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google Scholar). we that Hsp33 a major in protecting these cells against heat While cells that Hsp33 well the where both and Hsp33 proteins are to form these conditions of oxidative stress and heat This by the cells with a Hsp33 that the to the of Hsp33. of cells not not that the of Hsp33 is conditions but for cells heat stress This that the redox-regulated Hsp33 is for high in cells that are To the dimerization of oxidized Hsp33 monomers is for the of Hsp33 to cells against this severe stress we cells with a the monomeric protein the that the of Hsp33 this with the of Hsp33 the not of these cells heat that the constitutively monomeric Hsp33 to the cells against this combination of heat and oxidative stress cells were to form and very to cells the Hsp33 This that conditions of severe oxidative heat dimerization of Hsp33 is for not that oxidized Hsp33 monomers a oxidative stress conditions in vivo, where and proteins and which are not by an The Zinc in that were with the constitutively monomeric protein were of the that were with the Hsp33 (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Biol. PubMed Scopus Google Scholar). This which four highly conserved as well as the two conserved is to coordinate is to to oxidative stress by the formation of disulfide bonds, and is to of the in vitro chaperone activity of the Hsp33 protein with the chaperone activity of the oxidized that it is not disulfide bond formation that causes the partial activation of the chaperone activity of Hsp33 but that it is the of zinc the oxidized the Hsp33 protein inactive as a molecular chaperone with (5Graumann J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google and not but active with Biol. PubMed Scopus Google and not This that reducing conditions, the C-terminal zinc the substrate-binding site of rendering reduced Hsp33 zinc is by disulfide bond formation, zinc or the substrate-binding site of the Hsp33 is that Hsp33 conformational changes that causes the exposure of in the protein PubMed Scopus Google Scholar). these were to the substrate-binding site in Hsp33 as we that of zinc to or to disulfide bond formation the exposure of in Hsp33. To the of four Hsp33 conformations, we the a very with an of in but a in as well as a in to a environment PubMed Scopus Google Scholar). In with we found that oxidized Hsp33 very and a in the of and monomers very and of the binding of the Hsp33 in with the oxidized and that it is the zinc binding in reduced Hsp33 that is for the of Hsp33 and Hsp33 inactive and of zinc by of the or oxidative stress disulfide bond formation leads to the of an of and to the partial activation of the chaperone of Hsp33. Hsp33 Zinc and conformational changes in Hsp33 zinc release and that and the dimerization of Hsp33. the that are the of the of an Hsp33 that of the redox active C terminus J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Biol. PubMed Scopus Google Scholar). In which that Hsp33 conformational changes with an of α-helical and a in PubMed Scopus Google Scholar). these the of Hsp33 protein in the reduced, monomeric or the oxidized conformation, the of conformational the of the conformational changes To in Hsp33 causes conformational in the we the of four Hsp33 that reduced, and monomers a high α-helical a and In the of zinc a in the of α-helical This that it is zinc binding that stabilizes Hsp33 in a and that of zinc causes unfolding of the This with which a of reduced Hsp33 monomers as with Hsp33 monomers (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google J. Lilie H. J. M. Bardwell J.C.A. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). both oxidized monomers as well as oxidized Hsp33 a further in α-helical and in that disulfide bond formation causes an further unfolding of Hsp33. the oxidized Hsp33 and to we these that of the changes the activation process of Hsp33 take place the of the reduced to the oxidized The activation that the dimerization process of and which is in a affinity for highly unfolding is to an in the of the binding site to changes in the structure. The C-terminal of Hsp33 and Zinc we not which of Hsp33 are in the major unfolding that to the activation process of Hsp33. In an to where the unfolding in we to the and of the C-terminal redox The of coli together with the two J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Biol. PubMed Scopus Google to C-terminal fragments of the protein that were and in The and were found to both in with zinc and reducing both Hsp33 fragments to well an and not of the zinc and redox that the one of zinc which by the oxidative formation of two disulfide bonds not This that the C-terminal domain of Hsp33 is an which its zinc binding and its redox zinc by with by a of the that zinc the of the C-terminal redox of the of the zinc reduced redox domain with that of the redox that disulfide bond formation causes an in and The to These were that disulfide bonds are known to protein and to not to a further unfolding of a the combination of of to of zinc and formation of disulfide bonds cysteines that these major unfolding these were in with of the Hsp33 protein that a of concomitant with disulfide bond formation and in to the of that zinc To investigate of the conformational changes are to the C-terminal redox domain of Hsp33 or the chaperone we the for the reduced and oxidized C-terminal Hsp33 with the for reduced and oxidized Hsp33 of the reduced and oxidized that the C-terminal Hsp33 domain is well and monomeric reduced and but and appears in a of oxidized and reduced redox The of the C-terminal in the reduced, zinc-bound state and in the oxidized state were then in the NMR of the protein and of the of reduced, Hsp33 with the reduced, C-terminal is in of in an that the of the C-terminal domain is very in the and the with the C-terminal domain of we found that of Hsp33 changes in the NMR of in the of the a that the of This is an that the oxidized C-terminal domain is in the protein as of the in the two in are or very that a major of the the of the NMR of Hsp33 and C-terminal of reduced, Hsp33 in with the of reduced and in The of the that are in the two of the of reduced, zinc-bound Hsp33 and oxidized Hsp33 of an of of reduced, zinc-bound Hsp33 disulfide Hsp33 and the reduced, zinc-bound of the in the reduced, zinc-bound are not in that of the oxidized an of NMR of reduced, zinc-bound Hsp33 oxidized Hsp33 and the reduced, zinc-bound of the and are these to which not In two with the oxidized are but the reduced with that of the reduced that it belongs to a in the C-terminal of the the oxidized is to a of the is an that the of the C-terminal domain is The molecular chaperone Hsp33 belongs to a class of proteins, whose activity is These proteins in highly conserved cysteines, which are to and are both in vitro and in Upon of the proteins as Hsp33 (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google protein C J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google and M. PubMed Scopus Google are proteins J. W. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google are redox-regulated protein affinity to regulatory proteins as M.S. Buttner M.J. J. 1999; PubMed Scopus Google or S. J. PubMed Scopus Google their redox In a of redox-regulated proteins, zinc found to of the redox This for the in S. W. J. J. Biol. Chem. Full Text PDF PubMed Google the M.S. W. Buttner M.J. PubMed Scopus Google as well as Hsp33 (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). the highly conserved cysteines coordinate zinc reducing Upon exposure of proteins to oxidative disulfide bonds and zinc is Upon to conditions, the cysteines are reduced, and zinc is is known the changes that are by disulfide bond formation in redox-regulated proteins and which to the in protein To investigate this we to the redox-regulated chaperone Hsp33 as a whose activation process three Hsp33 the reduced inactive Hsp33 monomer, the oxidized Hsp33 monomer, and the fully active oxidized Hsp33 In reduced, monomeric four cysteines are in the high affinity binding of We found that zinc in it the cysteines for a by and allows the disulfide bonds to form (3Jakob U. Eser M. Bardwell J.C.A. J. Biol. Chem. 2000; 275: 38302-38310Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). is the that zinc the chaperone of Hsp33 reducing The C-terminal redox domain of Hsp33 is fully a α-helical zinc is This zinc-binding domain appears to the substrate-binding site of Hsp33 by with unfolding of by the of zinc or by the of that the C-terminal redox domain of Hsp33 and causes the C-terminal domain to This and the chaperone of Hsp33 to a that allows Hsp33 to unfolding proteins and to the this partially of Hsp33 appears to formation of the two disulfide bonds, Hsp33 further This further unfolding for the dimerization of oxidized Hsp33 monomers and for the activation of the chaperone of Hsp33. Upon disulfide bond formation, very appears to in the C-terminal domain of Hsp33 as in the C-terminal as well as in Hsp33. in the of the Hsp33 the of the C-terminal domain are domain and three and two to the in the is a that by the protein or the terminus of Hsp33 as a for the of the C terminus to their in Hsp33. the C terminus of the Hsp33 as in the not the of the oxidized Hsp33 is by the that the two of Hsp33 are very Hsp33 conditions Biol. PubMed Scopus Google or conditions J. J. Jakob U. Full Text Full Text PDF PubMed Scopus Google Scholar). In that the which the dimerization and the binding site of is largely by the redox conformational the unfolding of the C-terminal domain of Hsp33 not the of Hsp33 or the C-terminal domain and appears to fully of reducing conditions both in vitro and in While zinc binding is well known to to proteins, and zinc-binding found to as Chem. Biol. 2000; PubMed Scopus Google and unfolding of zinc-binding as of a regulatory high affinity zinc to redox and H. PubMed Scopus Google Scholar). a of proteins as the zinc proteins W. U. S. PubMed Scopus Google W. U. S. PubMed Scopus Google protein C J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google U. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and U. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google found to and release zinc their high affinity zinc binding the redox conditions of the in proteins where the of changes zinc it not unfolding of the zinc-binding domain an as of an protein to highly the where it zinc W. J. 2003; PubMed Scopus Google Scholar). This then the to the of a and as is the for or its or in Hsp33 appears not to the redox-regulated protein whose to Under conditions, the zinc-binding of to and the oxidative stress Upon exposure to oxidative disulfide bonds of and zinc is This is by major that to the release of which is then to of its M.S. Buttner M.J. J. 1999; PubMed Scopus Google M.S. Buttner M.J. PubMed Scopus Google Scholar). In to Hsp33 where the oxidized and the reduced zinc-bound is fully appears to α-helical the reduced, zinc-bound This then leads to the of oxidized native W. M.J. Buttner M.J. M.S. J. Biol. 2003; PubMed Scopus Google Scholar). This is in to where the reduced, found to a (2Jakob U. Muse W. Eser M. Bardwell J.C.A. Cell. 1999; 96: 341-352Abstract Full Text Full Text PDF PubMed Scopus (429) Google Scholar). Hsp33 and in to their conformational to with the of disulfide In the disulfide bonds are cysteines in the This appears to conformational causes the C-terminal domain to its and leads to the exposure of that are capable of with the unfolding proteins of Hsp33. In the disulfide bonds are cysteines that are in the and or W. M.J. Buttner M.J. M.S. J. Biol. 2003; PubMed Scopus Google Scholar). of disulfide bonds appears to to a the that with in the of reduced and oxidized Hsp33 PubMed Scopus Google Scholar). that these conformational changes are to the C-terminal redox switch The nature of Hsp33 allows the terminus to its for dimerization and binding in the reduced, inactive that Hsp33 to activated is the the C-terminal redox This domain is in its it is fully and the substrate-binding The switch is oxidative disulfide bond formation causes zinc the redox switch domain dimerization of two oxidized Hsp33 monomers and the formation of a highly active molecular We for this and for the and monomeric in Hsp33. We are to for and for the We Bardwell and for this