Understanding the Functional Interplay between Mammalian Mitochondrial Hsp70 Chaperone Machine Components

Abstract

Mitochondria biogenesis requires the import of several precursor proteins that are synthesized in the cytosol. The mitochondrial heat shock protein 70 (mtHsp70) machinery components are highly conserved among eukaryotes, including humans. However, the functional properties of human mtHsp70 machinery components have not been characterized among all eukaryotic families. To study the functional interactions, we have reconstituted the components of the mtHsp70 chaperone machine (Hsp70/J-protein/GrpE/Hep) and systematically analyzed in vitro conditions for biochemical functions. We observed that the sequence-specific interaction of human mtHsp70 toward mitochondrial client proteins differs significantly from its yeast counterpart Ssc1. Interestingly, the helical lid of human mtHsp70 was found dispensable to the binding of P5 peptide as compared with the other Hsp70s. We observed that the two human mitochondrial matrix J-protein splice variants differentially regulate the mtHsp70 chaperone cycle. Strikingly, our results demonstrated that human Hsp70 escort protein (Hep) possesses a unique ability to stimulate the ATPase activity of mtHsp70 as well as to prevent the aggregation of unfolded client proteins similar to J-proteins. We observed that Hep binds with the C terminus of mtHsp70 in a full-length context and this interaction is distinctly different from unfolded client-specific or J-protein binding. In addition, we found that the interaction of Hep at the C terminus of mtHsp70 is regulated by the helical lid region. However, the interaction of Hep at the ATPase domain of the human mtHsp70 is mutually exclusive with J-proteins, thus promoting a similar conformational change that leads to ATPase stimulation. Additionally, we highlight the biochemical defects of the mtHsp70 mutant (G489E) associated with a myelodysplastic syndrome. Mitochondria biogenesis requires the import of several precursor proteins that are synthesized in the cytosol. The mitochondrial heat shock protein 70 (mtHsp70) machinery components are highly conserved among eukaryotes, including humans. However, the functional properties of human mtHsp70 machinery components have not been characterized among all eukaryotic families. To study the functional interactions, we have reconstituted the components of the mtHsp70 chaperone machine (Hsp70/J-protein/GrpE/Hep) and systematically analyzed in vitro conditions for biochemical functions. We observed that the sequence-specific interaction of human mtHsp70 toward mitochondrial client proteins differs significantly from its yeast counterpart Ssc1. Interestingly, the helical lid of human mtHsp70 was found dispensable to the binding of P5 peptide as compared with the other Hsp70s. We observed that the two human mitochondrial matrix J-protein splice variants differentially regulate the mtHsp70 chaperone cycle. Strikingly, our results demonstrated that human Hsp70 escort protein (Hep) possesses a unique ability to stimulate the ATPase activity of mtHsp70 as well as to prevent the aggregation of unfolded client proteins similar to J-proteins. We observed that Hep binds with the C terminus of mtHsp70 in a full-length context and this interaction is distinctly different from unfolded client-specific or J-protein binding. In addition, we found that the interaction of Hep at the C terminus of mtHsp70 is regulated by the helical lid region. However, the interaction of Hep at the ATPase domain of the human mtHsp70 is mutually exclusive with J-proteins, thus promoting a similar conformational change that leads to ATPase stimulation. Additionally, we highlight the biochemical defects of the mtHsp70 mutant (G489E) associated with a myelodysplastic syndrome. IntroductionMitochondria are ubiquitous, complex, and essential organelles of eukaryotes. Several biochemical reactions in iron metabolism, amino acid biosynthesis, urea metabolism, nucleotide biosynthesis, fatty acid metabolism, and oxidative phosphorylation are carried out within this organelle (1Hatefi Y. Annu. Rev. Biochem. 1985; 54: 1015-1069Crossref PubMed Google Scholar). More than 98% of the proteins that comprise mitochondria are encoded by the nuclear genome (2Bolender N. Sickmann A. Wagner R. Meisinger C. Pfanner N. EMBO Rep. 2008; 9: 42-49Crossref PubMed Scopus (235) Google Scholar, 3Neupert W. Hartl F.U. Craig E.A. Pfanner N. Cell. 1990; 63: 447-450Abstract Full Text PDF PubMed Scopus (182) Google Scholar, 4Pfanner N. Geissler A. Nat. Rev. Mol. Cell Biol. 2001; 2: 339-349Crossref PubMed Scopus (416) Google Scholar). Because a vast majority of proteins in the mitochondrial matrix are synthesized on cytosolic ribosomes, efficient import of proteins is critical for mitochondrial function (2Bolender N. Sickmann A. Wagner R. Meisinger C. Pfanner N. EMBO Rep. 2008; 9: 42-49Crossref PubMed Scopus (235) Google Scholar, 3Neupert W. Hartl F.U. Craig E.A. Pfanner N. Cell. 1990; 63: 447-450Abstract Full Text PDF PubMed Scopus (182) Google Scholar, 5Neupert W. Brunner M. Nat. Rev. Mol. Cell Biol. 2002; 3: 555-565Crossref PubMed Scopus (298) Google Scholar, 6Voisine C. Craig E.A. Zufall N. von Ahsen O. Pfanner N. Voos W. Cell. 1999; 97: 565-574Abstract Full Text Full Text PDF PubMed Scopus (210) Google Scholar). This is assisted by mitochondrial chaperone machinery consisting of the 70-kDa family (mtHsp70), 2The abbreviations used are: mtHsp70mitochondrial Hsp70SBDsubstrate binding domainHephuman escort proteinGSTglutathione S-transferaseMDSmyelodysplastic syndromeGRPglucose-regulated protein. J-proteins, and nucleotide exchange factors, which are critical for several cellular functions, including preprotein translocation and their subsequent folding inside the mitochondrial matrix (5Neupert W. Brunner M. Nat. Rev. Mol. Cell Biol. 2002; 3: 555-565Crossref PubMed Scopus (298) Google Scholar, 7Mayer M.P. Bukau B. Cell. Mol. Life Sci. 2005; 62: 670-684Crossref PubMed Scopus (2019) Google Scholar).The mtHsp70 chaperone machinery components are highly conserved across species, including in mammalian mitochondria (8Schilke B. Williams B. Knieszner H. Pukszta S. D'Silva P. Craig E.A. Marszalek J. Curr. Biol. 2006; 16: 1660-1665Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). The mtHsp70s are the most abundant and are usually present as one or two copies in the mammalian mitochondrial matrix compartment (9Kaul S.C. Deocaris C.C. Wadhwa R. Exp. Gerontol. 2007; 42: 263-274Crossref PubMed Scopus (200) Google Scholar, 10Kaul S.C. Duncan E. Sugihara T. Reddel R.R. Mitsui Y. Wadhwa R. DNA Res. 2000; 7: 229-231Crossref PubMed Scopus (25) Google Scholar). In the mammalian system, human mtHsp70 is commonly referred to as “mortalin” or glucose-regulated protein (GRP75) (11Bhattacharyya T. Karnezis A.N. Murphy S.P. Hoang T. Freeman B.C. Phillips B. Morimoto R.I. J. Biol. Chem. 1995; 270: 1705-1710Abstract Full Text Full Text PDF PubMed Scopus (187) Google Scholar, 12Mizzen L.A. Chang C. Garrels J.I. Welch W.J. J. Biol. Chem. 1989; 264: 20664-20675Abstract Full Text PDF PubMed Google Scholar). The mouse mitochondrion contains two isoforms of mtHsp70 termed as “mot-1” and “mot-2.” Both isoforms are involved in several important cellular processes. In contrast to murines, human mitochondria have only one mtHsp70 encoded by the HSPA9 gene, which functionally corresponds to mouse mot-2 (9Kaul S.C. Deocaris C.C. Wadhwa R. Exp. Gerontol. 2007; 42: 263-274Crossref PubMed Scopus (200) Google Scholar, 10Kaul S.C. Duncan E. Sugihara T. Reddel R.R. Mitsui Y. Wadhwa R. DNA Res. 2000; 7: 229-231Crossref PubMed Scopus (25) Google Scholar). Similarly, in human mitochondria, there are two members of type-I class Hsp40 isoforms reported, which are usually referred to as hTid-1L (Larger isoform) and hTid-1S (Smaller isoform). However, the physiological importance of these two J-proteins is still unclear (13Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 8499-8504Crossref PubMed Scopus (121) Google Scholar). The different nucleotide states of human mtHsp70 are regulated by the nucleotide exchange factor: human GrpEL1 (14Choglay A.A. Chapple J.P. Blatch G.L. Cheetham M.E. Gene. 2001; 267: 125-134Crossref PubMed Scopus (17) Google Scholar, 15Laloraya S. Gambill B.D. Craig E.A. Proc. Natl. Acad. Sci. U.S.A. 1994; 91: 6481-6485Crossref PubMed Scopus (136) Google Scholar). Similarly, a mammalian mitochondrion also possesses an ortholog of recently discovered “yeast Zim17” termed as hsp70 escort protein, “Hep” (16Burri L. Vascotto K. Fredersdorf S. Tiedt R. Hall M.N. Lithgow T. J. Biol. Chem. 2004; 279: 50243-50249Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 17Sichting M. Mokranjac D. Azem A. Neupert W. Hell K. EMBO J. 2005; 24: 1046-1056Crossref PubMed Scopus (76) Google Scholar). The physiological role of Hep in human mitochondrial matrix compartment is poorly understood. In vivo, the functional cycle of interaction of an unfolded mitochondrial client protein is initiated in the ATP-bound state of mtHsp70. The binding of the client protein in the peptide binding cleft and simultaneous interaction of J-domains of J-proteins with the ATPase domain of Hsp70 results in ATP hydrolysis, and thus stabilizes the interaction of a client polypeptide by converting Hsp70 to the ADP-bound state (18Bukau B. Horwich A.L. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2404) Google Scholar). Nucleotide release factors cause exchange of ADP for ATP, resulting in dissociation of bound clients, and prime Hsp70 for a second cycle of interaction (19Laufen T. Mayer M.P. Beisel C. Klostermeier D. Mogk A. Reinstein J. Bukau B. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 5452-5457Crossref PubMed Scopus (464) Google Scholar, 20McCarty J.S. Buchberger A. Reinstein J. Bukau B. J. Mol. Biol. 1995; 249: 126-137Crossref PubMed Scopus (349) Google Scholar, 21Rajan V.B. D'Silva P. Funct. Integr. Genomics. 2009; 9: 433-446Crossref PubMed Scopus (124) Google Scholar).In the mammalian system, the mtHsp70 machinery plays a very critical functional role for protein quality control in the matrix compartment, thereby regulating mitochondria biogenesis. Importantly, the altered expression and specific mutations in the mtHsp70 chaperone machinery lead to severe mitochondrial disorders. In humans, the levels of mtHsp70 are highly up-regulated in all types of tumors and have been used as biomarkers to detect tumor invasiveness (22Wadhwa R. Takano S. Kaur K. Deocaris C.C. Pereira-Smith O.M. Reddel R.R. Kaul S.C. Int. J. Cancer. 2006; 118: 2973-2980Crossref PubMed Scopus (192) Google Scholar). Reduced expression of mtHsp70 is commonly observed in Parkinson disease and other age-related diseases leading to mitochondrial dysfunction (23Leverenz J.B. Umar I. Wang Q. Montine T.J. McMillan P.J. Tsuang D.W. Jin J. Pan C. Shin J. Zhu D. Zhang J. Brain Pathol. 2007; 17: 139-145Crossref PubMed Scopus (163) Google Scholar). In zebrafish, a single point mutation in the C-terminal region of mtHsp70 (G492E, referred as MDS mutant) is associated with a hematopoietic defect similar to the myelodysplastic syndrome, presumably due to loss of chaperone function (24Craven S.E. French D. Ye W. de Sauvage F. Rosenthal A. Blood. 2005; 105: 3528-3534Crossref PubMed Scopus (87) Google Scholar). Recently, it has been shown that altered expression of mammalian Hsp40 isoforms (hTid-1L and hTid-1S) leads to several cellular phenotypes, including apoptosis, malignancy, and cardiac-related disorders such as dilated cardiomyopathic syndrome (13Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 8499-8504Crossref PubMed Scopus (121) Google Scholar, 25Hayashi M. Imanaka-Yoshida K. Yoshida T. Wood M. Fearns C. Tatake R.J. Lee J.D. Nat. Med. 2006; 12: 128-132Crossref PubMed Scopus (67) Google Scholar). Despite these critical cellular roles, little functional information at the biochemical level of human mtHsp70 chaperone machinery is available.To address the functional importance of mammalian mtHsp70 chaperone machinery components in mitochondria biogenesis, we have undertaken the of the human mtHsp70 machine to its unique properties at the biochemical level as compared with the well several biochemical that are from other Hsp70 and are critical for the mammalian mitochondrial mtHsp70 is highly conserved across species, we observed in sequence-specific binding toward mitochondrial client proteins and the of such as J-proteins. our it is that such are to in the of the binding domain the Additionally, we have several properties of such as its unique to stimulate ATPase activity of mtHsp70 as well as of aggregation of unfolded we have several biochemical defects associated with the MDS mutant to the functional of mtHsp70 machinery in disease in this study was to the of of components of the mitochondrial chaperone machine in human To the of mammalian mitochondrial Hsp70 chaperone we reconstituted and analyzed the chaperone properties of the human mtHsp70 chaperone machine components well in vitro biochemical and biochemical that are important for the chaperone function of human mtHsp70 and its a sequence-specific interaction of human mtHsp70 with the peptide from mitochondrial of client Importantly, human mtHsp70 very toward and peptide such as it toward that such as compared with yeast Ssc1. C-terminal helical lid to with the P5 peptide to the that the of human mtHsp70 possesses a as compared with E. and Ssc1. it has been demonstrated that the of in ADP-bound state as compared with thus promoting it J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). However, our that the of human mtHsp70 for P5 as compared with we that the and of a amino acid helical lid the of human mtHsp70 significantly differs compared with other second the of of the chaperone activity of human mtHsp70 by J-protein splice hTid-1L and that hTid-1S is efficient in regulating the ATPase cycle of mtHsp70 due to its activity as compared with This an the of amino from the C-terminal of hTid-1L in regulating its ability to stimulate the ATPase activity of mtHsp70. the other it is that an of amino at the C terminus of hTid-1S leads to of thus J-protein isoforms in aggregation of The functional these two J-protein variants the for at the cellular level as (13Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 8499-8504Crossref PubMed Scopus (121) Google our a in which the Hep protein the chaperone function of human mtHsp70. the that the of Hep interaction is also on the C-terminal region of human mtHsp70. on our we that C-terminal domain and are involved in regulating the Hep interaction in protein. This is by two important the of C to the interaction of Hep in the of the a of the level of interaction in and that amino from to critical for Hep binding at the C terminus of human mtHsp70. Similarly, an interaction with Hep was also observed in or human mtHsp70 cleft due to of C-terminal of amino to in these However, the by C-terminal and in mutant proteins due to in the of these to the the other we not out the that of and the of the and ATPase domain of human mtHsp70 by the of the thus promoting a for Hep binding in and point are in of this the region has been shown to a critical role for binding to the ATPase domain of mtHsp70 in yeast M. M. K. Mokranjac D. Neupert W. Hell K. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in the domain in a to in or the ATP-bound state thereby their binding with Hep protein. the functional of C-terminal and is well in B. 42: PubMed Scopus Google Scholar). the importance of and in regulating the interaction of Hep with mtHsp70 in human of Hep interaction at the C terminus of human mtHsp70 is unique and from or J-proteins. biochemical our The mtHsp70 in the or of is not by levels of P5 its different of interaction at the C and point of human mtHsp70 significantly their ability to stimulate ATPase activity as compared with J-proteins. However, the Hep interaction with the human mtHsp70 not in of ATPase We that the interaction the C terminus of human mtHsp70 is dispensable for the conformational for of the ATPase domain to the the of Hep a unique ability to stimulate ATPase activity of human mtHsp70. However, we out the of Hep as a nucleotide exchange as on the activity of Hep observed in single P. C. S. J. Biol. Chem. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar). our biochemical that the of Hep the type-I J-protein To the of we have critical amino acid of the terminus of human mtHsp70 that are essential for the conformational ATP these found with that are essential for J-protein by and hTid-1S for E. and human binding of hTid-1S out by Hep or that the interaction of these two proteins at the ATPase domain of human mtHsp70 are mutually The in binding Hep and hTid-1S that similar conformational in the ATPase domain that results in of ATP However, the at which conformational to the ATP in the chaperone cycle due to in ATPase with Hsp70 our in vitro biochemical that Hep also possesses human functions. Hep chaperone it unfolded such as its aggregation in the of the Hsp70 protein similar to type-I J-proteins. on these by we that Hep a of a class of for Hsp70 for eukaryotic mitochondria biogenesis. However, the specific mitochondrial client protein other than Hsp70 the of Hep to prevent aggregation in to physiological is to on the functional defects associated with MDS The mutant defects in with J-protein and as well as the of nucleotide exchange ability by The ATPase activity is significantly and with the loss of by client an defect associated with this we that the loss of mtHsp70 activity in the MDS mutant the import of precursor proteins and their subsequent folding in the matrix leading to mitochondrial results that the loss of chaperone function the leading cause of myelodysplastic syndrome. To the importance of this in other we a similar mutation at the in yeast which in a the importance of this in the of mtHsp70. B. and P. biochemical of this syndrome at the physiological our results and highlight several unique and biochemical of the human mitochondrial chaperone machine that are for protein quality control in the mitochondrial Additionally, it the for for mitochondria biogenesis for cellular in the mammalian our also to the of chaperone function in a state such as myelodysplastic syndrome. our results a for the on in mitochondrial disorders. IntroductionMitochondria are ubiquitous, complex, and essential organelles of eukaryotes. Several biochemical reactions in iron metabolism, amino acid biosynthesis, urea metabolism, nucleotide biosynthesis, fatty acid metabolism, and oxidative phosphorylation are carried out within this organelle (1Hatefi Y. Annu. Rev. Biochem. 1985; 54: 1015-1069Crossref PubMed Google Scholar). More than 98% of the proteins that comprise mitochondria are encoded by the nuclear genome (2Bolender N. Sickmann A. Wagner R. Meisinger C. Pfanner N. EMBO Rep. 2008; 9: 42-49Crossref PubMed Scopus (235) Google Scholar, 3Neupert W. Hartl F.U. Craig E.A. Pfanner N. Cell. 1990; 63: 447-450Abstract Full Text PDF PubMed Scopus (182) Google Scholar, 4Pfanner N. Geissler A. Nat. Rev. Mol. Cell Biol. 2001; 2: 339-349Crossref PubMed Scopus (416) Google Scholar). Because a vast majority of proteins in the mitochondrial matrix are synthesized on cytosolic ribosomes, efficient import of proteins is critical for mitochondrial function (2Bolender N. Sickmann A. Wagner R. Meisinger C. Pfanner N. EMBO Rep. 2008; 9: 42-49Crossref PubMed Scopus (235) Google Scholar, 3Neupert W. Hartl F.U. Craig E.A. Pfanner N. Cell. 1990; 63: 447-450Abstract Full Text PDF PubMed Scopus (182) Google Scholar, 5Neupert W. Brunner M. Nat. Rev. Mol. Cell Biol. 2002; 3: 555-565Crossref PubMed Scopus (298) Google Scholar, 6Voisine C. Craig E.A. Zufall N. von Ahsen O. Pfanner N. Voos W. Cell. 1999; 97: 565-574Abstract Full Text Full Text PDF PubMed Scopus (210) Google Scholar). This is assisted by mitochondrial chaperone machinery consisting of the 70-kDa family (mtHsp70), 2The abbreviations used are: mtHsp70mitochondrial Hsp70SBDsubstrate binding domainHephuman escort proteinGSTglutathione S-transferaseMDSmyelodysplastic syndromeGRPglucose-regulated protein. J-proteins, and nucleotide exchange factors, which are critical for several cellular functions, including preprotein translocation and their subsequent folding inside the mitochondrial matrix (5Neupert W. Brunner M. Nat. Rev. Mol. Cell Biol. 2002; 3: 555-565Crossref PubMed Scopus (298) Google Scholar, 7Mayer M.P. Bukau B. Cell. Mol. Life Sci. 2005; 62: 670-684Crossref PubMed Scopus (2019) Google Scholar).The mtHsp70 chaperone machinery components are highly conserved across species, including in mammalian mitochondria (8Schilke B. Williams B. Knieszner H. Pukszta S. D'Silva P. Craig E.A. Marszalek J. Curr. Biol. 2006; 16: 1660-1665Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). The mtHsp70s are the most abundant and are usually present as one or two copies in the mammalian mitochondrial matrix compartment (9Kaul S.C. Deocaris C.C. Wadhwa R. Exp. Gerontol. 2007; 42: 263-274Crossref PubMed Scopus (200) Google Scholar, 10Kaul S.C. Duncan E. Sugihara T. Reddel R.R. Mitsui Y. Wadhwa R. DNA Res. 2000; 7: 229-231Crossref PubMed Scopus (25) Google Scholar). In the mammalian system, human mtHsp70 is commonly referred to as “mortalin” or glucose-regulated protein (GRP75) (11Bhattacharyya T. Karnezis A.N. Murphy S.P. Hoang T. Freeman B.C. Phillips B. Morimoto R.I. J. Biol. Chem. 1995; 270: 1705-1710Abstract Full Text Full Text PDF PubMed Scopus (187) Google Scholar, 12Mizzen L.A. Chang C. Garrels J.I. Welch W.J. J. Biol. Chem. 1989; 264: 20664-20675Abstract Full Text PDF PubMed Google Scholar). The mouse mitochondrion contains two isoforms of mtHsp70 termed as “mot-1” and “mot-2.” Both isoforms are involved in several important cellular processes. In contrast to murines, human mitochondria have only one mtHsp70 encoded by the HSPA9 gene, which functionally corresponds to mouse mot-2 (9Kaul S.C. Deocaris C.C. Wadhwa R. Exp. Gerontol. 2007; 42: 263-274Crossref PubMed Scopus (200) Google Scholar, 10Kaul S.C. Duncan E. Sugihara T. Reddel R.R. Mitsui Y. Wadhwa R. DNA Res. 2000; 7: 229-231Crossref PubMed Scopus (25) Google Scholar). Similarly, in human mitochondria, there are two members of type-I class Hsp40 isoforms reported, which are usually referred to as hTid-1L (Larger isoform) and hTid-1S (Smaller isoform). However, the physiological importance of these two J-proteins is still unclear (13Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 8499-8504Crossref PubMed Scopus (121) Google Scholar). The different nucleotide states of human mtHsp70 are regulated by the nucleotide exchange factor: human GrpEL1 (14Choglay A.A. Chapple J.P. Blatch G.L. Cheetham M.E. Gene. 2001; 267: 125-134Crossref PubMed Scopus (17) Google Scholar, 15Laloraya S. Gambill B.D. Craig E.A. Proc. Natl. Acad. Sci. U.S.A. 1994; 91: 6481-6485Crossref PubMed Scopus (136) Google Scholar). Similarly, a mammalian mitochondrion also possesses an ortholog of recently discovered “yeast Zim17” termed as hsp70 escort protein, “Hep” (16Burri L. Vascotto K. Fredersdorf S. Tiedt R. Hall M.N. Lithgow T. J. Biol. Chem. 2004; 279: 50243-50249Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 17Sichting M. Mokranjac D. Azem A. Neupert W. Hell K. EMBO J. 2005; 24: 1046-1056Crossref PubMed Scopus (76) Google Scholar). The physiological role of Hep in human mitochondrial matrix compartment is poorly understood. In vivo, the functional cycle of interaction of an unfolded mitochondrial client protein is initiated in the ATP-bound state of mtHsp70. The binding of the client protein in the peptide binding cleft and simultaneous interaction of J-domains of J-proteins with the ATPase domain of Hsp70 results in ATP hydrolysis, and thus stabilizes the interaction of a client polypeptide by converting Hsp70 to the ADP-bound state (18Bukau B. Horwich A.L. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2404) Google Scholar). Nucleotide release factors cause exchange of ADP for ATP, resulting in dissociation of bound clients, and prime Hsp70 for a second cycle of interaction (19Laufen T. Mayer M.P. Beisel C. Klostermeier D. Mogk A. Reinstein J. Bukau B. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 5452-5457Crossref PubMed Scopus (464) Google Scholar, 20McCarty J.S. Buchberger A. Reinstein J. Bukau B. J. Mol. Biol. 1995; 249: 126-137Crossref PubMed Scopus (349) Google Scholar, 21Rajan V.B. D'Silva P. Funct. Integr. Genomics. 2009; 9: 433-446Crossref PubMed Scopus (124) Google Scholar).In the mammalian system, the mtHsp70 machinery plays a very critical functional role for protein quality control in the matrix compartment, thereby regulating mitochondria biogenesis. Importantly, the altered expression and specific mutations in the mtHsp70 chaperone machinery lead to severe mitochondrial disorders. In humans, the levels of mtHsp70 are highly up-regulated in all types of tumors and have been used as biomarkers to detect tumor invasiveness (22Wadhwa R. Takano S. Kaur K. Deocaris C.C. Pereira-Smith O.M. Reddel R.R. Kaul S.C. Int. J. Cancer. 2006; 118: 2973-2980Crossref PubMed Scopus (192) Google Scholar). Reduced expression of mtHsp70 is commonly observed in Parkinson disease and other age-related diseases leading to mitochondrial dysfunction (23Leverenz J.B. Umar I. Wang Q. Montine T.J. McMillan P.J. Tsuang D.W. Jin J. Pan C. Shin J. Zhu D. Zhang J. Brain Pathol. 2007; 17: 139-145Crossref PubMed Scopus (163) Google Scholar). In zebrafish, a single point mutation in the C-terminal region of mtHsp70 (G492E, referred as MDS mutant) is associated with a hematopoietic defect similar to the myelodysplastic syndrome, presumably due to loss of chaperone function (24Craven S.E. French D. Ye W. de Sauvage F. Rosenthal A. Blood. 2005; 105: 3528-3534Crossref PubMed Scopus (87) Google Scholar). Recently, it has been shown that altered expression of mammalian Hsp40 isoforms (hTid-1L and hTid-1S) leads to several cellular phenotypes, including apoptosis, malignancy, and cardiac-related disorders such as dilated cardiomyopathic syndrome (13Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 8499-8504Crossref PubMed Scopus (121) Google Scholar, 25Hayashi M. Imanaka-Yoshida K. Yoshida T. Wood M. Fearns C. Tatake R.J. Lee J.D. Nat. Med. 2006; 12: 128-132Crossref PubMed Scopus (67) Google Scholar). Despite these critical cellular roles, little functional information at the biochemical level of human mtHsp70 chaperone machinery is available.To address the functional importance of mammalian mtHsp70 chaperone machinery components in mitochondria biogenesis, we have undertaken the of the human mtHsp70 machine to its unique properties at the biochemical level as compared with the well several biochemical that are from other Hsp70 and are critical for the mammalian mitochondrial mtHsp70 is highly conserved across species, we observed in sequence-specific binding toward mitochondrial client proteins and the of such as J-proteins. our it is that such are to in the of the binding domain the Additionally, we have several properties of such as its unique to stimulate ATPase activity of mtHsp70 as well as of aggregation of unfolded we have several biochemical defects associated with the MDS mutant to the functional of mtHsp70 machinery in disease