Proteolytic Processing of the C Terminus of the α1CSubunit of L-type Calcium Channels and the Role of a Proline-rich Domain in Membrane Tethering of Proteolytic Fragments

Abstract

Although most L-type calcium channel α1C subunits isolated from heart or brain are ∼190-kDa proteins that lack ∼50 kDa of the C terminus, the C-terminal domain is present in intact cells. To test the hypothesis that the C terminus is processed but remains functionally associated with the channels, expressed, full-length α1C subunits were cleaved in vitro by chymotrypsin to generate a 190-kDa C-terminal truncated protein and C-terminal fragments of 30–56 kDa. These hydrophilic C-terminal fragments remained membrane-associated. A C-terminal proline-rich domain (PRD) was identified as the mediator of membrane association. The α1C PRD bound to SH3 domains in Src, Lyn, Hck, and the channel β2 subunit. Mutant α1C subunits lacking either ∼50 kDa of the C terminus or the PRD produced increased barium currents through the channels, demonstrating that these domains participate in the previously described (Wei, X., Neely, a., Lacerda, A. E. Olcese, r., Stefani, E., Perez-Reyes, E., and Birnbaumer, L. (1994) J. Biol. Chem. 269, 1635–1640) inhibition of channel function by the C terminus. Although most L-type calcium channel α1C subunits isolated from heart or brain are ∼190-kDa proteins that lack ∼50 kDa of the C terminus, the C-terminal domain is present in intact cells. To test the hypothesis that the C terminus is processed but remains functionally associated with the channels, expressed, full-length α1C subunits were cleaved in vitro by chymotrypsin to generate a 190-kDa C-terminal truncated protein and C-terminal fragments of 30–56 kDa. These hydrophilic C-terminal fragments remained membrane-associated. A C-terminal proline-rich domain (PRD) was identified as the mediator of membrane association. The α1C PRD bound to SH3 domains in Src, Lyn, Hck, and the channel β2 subunit. Mutant α1C subunits lacking either ∼50 kDa of the C terminus or the PRD produced increased barium currents through the channels, demonstrating that these domains participate in the previously described (Wei, X., Neely, a., Lacerda, A. E. Olcese, r., Stefani, E., Perez-Reyes, E., and Birnbaumer, L. (1994) J. Biol. Chem. 269, 1635–1640) inhibition of channel function by the C terminus. protein kinase A wild type in vitro translated polyacrylamide gel electrophoresis glutathioneS-transferase Src homology domain 3 proline-rich domain C-terminal L-type calcium channels form a subclass of voltage-gated calcium channels. Three different isoforms of α1 subunits (α1S, α1C, and α1D) serve as pore-forming subunits of the three groups of L-type channels: class S, class C, and class D. Two size forms for each of these isoforms have been detected in native tissues (1.De Jongh K.S. Warner C. Colvin A.A. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 10778-10782Crossref PubMed Scopus (122) Google Scholar, 2.Hell J.W. Yokoyama C.T. Wong S.T. Warner C. Snutch T.P. Catterall W.A. J. Biol. Chem. 1993; 268: 19451-19457Abstract Full Text PDF PubMed Google Scholar, 3.Hell J.W. Westenbroek R.E. Warner C. Ahlijanian M.K. Prystay W. Gilbert M.M. Snutch T.P. Catterall W.A. J. Cell Biol. 1993; 123: 949-962Crossref PubMed Scopus (625) Google Scholar, 4.De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-10402Crossref PubMed Scopus (236) Google Scholar, 5.Gao T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar), and in each case, the shorter forms correspond to proteins modified at the C terminus. For the α1D isoform, alternative splicing of mRNA may give rise to the short and long forms (6.Ihara Y. Yamada Y. Fujii Y. Gonoi T. Yano H. Yasuda K. Inagaki N. Seino Y. Seino S. Mol. Endocrinol. 1995; 9: 121-130PubMed Google Scholar). However, this does not appear to be the case for the α1C and α1S isoforms, and it appears that the shorter forms of the α1C and α1S proteins are generated by a post-translational, proteolytic processing event. In the case of these two proteins, it appears that processing would produce C-terminal fragments of 30–50 kDa (1.De Jongh K.S. Warner C. Colvin A.A. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 10778-10782Crossref PubMed Scopus (122) Google Scholar, 2.Hell J.W. Yokoyama C.T. Wong S.T. Warner C. Snutch T.P. Catterall W.A. J. Biol. Chem. 1993; 268: 19451-19457Abstract Full Text PDF PubMed Google Scholar, 3.Hell J.W. Westenbroek R.E. Warner C. Ahlijanian M.K. Prystay W. Gilbert M.M. Snutch T.P. Catterall W.A. J. Cell Biol. 1993; 123: 949-962Crossref PubMed Scopus (625) Google Scholar, 4.De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-10402Crossref PubMed Scopus (236) Google Scholar, 5.Gao T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). While little is known about the fate of the cleaved C-terminal domain, results obtained from immunofluorescence studies have suggested that the C terminus of the α1C is present in and with the of the α1C and the T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). the that the C-terminal fragments may functionally associated with the channels. The C-terminal of the α1C is in the class C calcium The of of the α1C been to be in the C terminus Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-10402Crossref PubMed Scopus (236) Google Scholar, T. Y. E. N. 1996; PubMed Scopus Google Scholar, T. A. H. Green N. Hosey M.M. 1997; Full Text Full Text PDF PubMed Scopus Google and the C-terminal truncated α1C and is not a for by in vitro Hosey M.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, H. J. M. H. J. 1991; PubMed Scopus Google Scholar, A. Takahashi M. S. H. S. PubMed Scopus Google Scholar). In the α1C C terminus appears to a in channel of to of the C terminus from the full-length α1C protein results in in with the full-length channel A. E. E. L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The C terminus of the α1C been to be in M. Y. L. E. Snutch T.P. 1995; PubMed Scopus Google Scholar, N. M. T. L. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Full Text Full Text PDF PubMed Scopus Google Scholar), and to the proteins N. M. T. L. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Full Text Full Text PDF PubMed Scopus Google and J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). the C terminus of α1C is a for the of the calcium and the proteolytic processing of the C terminus of channel the results from of the C terminus of α1C in intact that this domain is present and with the of the α1C and the β2 T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar), it is that the α1C is cleaved in and that the C-terminal of ∼50 kDa remains associated with the 190-kDa or with channel subunits or In to to this have to the processing of α1C and the of the C-terminal of this The of was to from heart as described previously H. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The in these were from were from The and C have been previously described A.J. R.E. Puri T.S. D. E. Hosey M.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). The for these are in A. The Cell was a from were isolated J. M. J. PubMed Google as described previously T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). were a and these were in the in vitro as described L-type calcium channels were from as described T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). of the α1C were generated with the the The of in the α1C was generated with three and two generated a at the C-terminal of the PRD and the at the of the The were to the PRD and the was to form the PRD The and of the α1C were the and were with the in by A.J. R.E. Puri T.S. D. E. Hosey M.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). Cell were were by at for The was in and were a or 3 of The was at for to and cells. The this was at for to the from the the was in a of and protein was to in the described of the α1C with or and of the and subunits in was as described T.S. Gerhardstein B.L. Hosey M.M. Biochemistry. 1997; PubMed Scopus Google Scholar). In vitro translated proteins were from the the and A protein was from by of and at the terminus. proteins were with and in the membrane from or either the α1C or with subunits were for as membrane and and with were at with of and for of as For of the channel with the α1C was to from isolated for either at or at to the of PubMed Scopus Google by and A.J. R.E. Puri T.S. D. E. Hosey M.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). were by of and and at for to the membrane and were by the membrane in of by to the membrane as described In of the α1C to chymotrypsin was as described previously T.S. Gerhardstein B.L. Hosey M.M. Biochemistry. 1997; PubMed Scopus Google Scholar). gel electrophoresis PubMed Scopus Google and was A.J. R.E. Puri T.S. D. E. Hosey M.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). were a were proteins the SH3 domains from Src, Lyn, Hck, or A. J. N. D. L. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar, A. N. S. D. 1996; PubMed Scopus Google or the SH3 domain of the subunit. The protein was generated by of the SH3 domain previously identified in the A.J. T. E. Hosey M.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and the was the and as by the In each the in vitro translated C-terminal protein from the α1C was in of to of to either or to of the proteins, and for at with The were with each of and the of was to The proteins bound to the were by to and proteins were detected by of the to the proteins was a α1C PRD The PRD was the as the and as the The of the PRD was by of the of the and α1C The PRD was to the at the of each of the C-terminal proteins, and the were as described were with the and the α1C or was in the and 3 of each was with the Y. Google Scholar), the the were were by the Y. Google Scholar). For the of currents through L-type calcium channels, the of and The was of and currents were in the of the Warner generated with a and with a currents were a and a were with a by for and were at and to were in to L-type calcium channels. were by the of the test from to a of the currents to the membrane were and currents were were to The were from at two different and are as In to to the processing of the native α1C from the protein to the 190-kDa and to the of the C-terminal fragments from the proteolytic of the α1C expressed, full-length α1C to a of to The was in by in the of the protein in T.S. Gerhardstein B.L. Hosey M.M. Biochemistry. 1997; PubMed Scopus Google Scholar). Although the native and brain α1C protein been isolated in the of a of J.W. Yokoyama C.T. Wong S.T. Warner C. Snutch T.P. Catterall W.A. J. Biol. Chem. 1993; 268: 19451-19457Abstract Full Text PDF PubMed Google T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar, Hosey M.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar), it was that the was from protein the expressed, full-length was to from to the proteolytic processed the α1C be in vitro with the α1C subunit. The were the with that proteolytic The results that a of the α1C either or with the β2 and was to may have been present and in the in the of the α1C was this protein was with or for at the were to at was a of the full-length the was to the α1C However, these the shorter was a C-terminal truncated 190-kDa form of the α1C this form of the protein was it would have been detected by the as this in the domains and These results suggested that the proteolytic of the native α1C isolated from was not from the of the α1C to the the native α1C would have been to not of the the not of the expressed, full-length α1C were in to the proteolytic processing with the native α1C subunit. The α1C in was to with a of in to the the α1C and to the of a with to the of the cleaved channel different were in vitro and The been suggested to the in J.W. Westenbroek R.E. C. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar). of these the α1C but that most is not for the of the channel in native produced the 190-kDa C-terminal truncated of the α1C with chymotrypsin generated a 190-kDa protein lacking C terminus as by the of the 190-kDa to the but not to the C the of the C terminus A and The 190-kDa of the α1C generated by chymotrypsin the as the native α1C isolated from of kDa was by the but not the C that it a from domain of In chymotrypsin generated C-terminal fragments of 30–56 kDa The C-terminal of kDa to the size the C-terminal domain was cleaved in a and to C suggested that it intact C terminus. The C-terminal fragments intact C as from C. chymotrypsin produce proteolytic that were to from the that in vitro with chymotrypsin for the of a to the and of the The of the C-terminal fragments was The C-terminal fragments and are hydrophilic A. K. T. T. Y. H. S. S. PubMed Scopus Google Scholar). However, of the the C-terminal fragments of the remained associated with the membrane and were not the studies were with chymotrypsin but to to the membrane and While the C-terminal fragments remained associated with the membrane of the that were the C-terminal fragments from the membrane to the of to the the of the C-terminal fragments from the membrane The of the C-terminal of the α1C in suggested that the membrane was to a The C-terminal fragments be to the truncated α1C present in the or with protein in the membrane for the of the α1C is that a that been identified to a in the of channel by T. Y. E. N. 1996; PubMed Scopus Google Scholar, T. A. H. Green N. Hosey M.M. 1997; Full Text Full Text PDF PubMed Scopus Google is to in the C-terminal domain that is In to test this at was present in the C-terminal fragments and to test of the fragments with the the fragments were in vitro with In the of two membrane the α1C were with and with the and to with chymotrypsin and for the of fragments of about kDa were by the and the from this a of the α1C remained by chymotrypsin and was by results were obtained the α1C were with and cleaved with chymotrypsin to of the C-terminal fragments with the C A of the C-terminal was isolated these and These results that a at Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-10402Crossref PubMed Scopus (236) Google Scholar, T. Y. E. N. 1996; PubMed Scopus Google Scholar, T. A. H. Green N. Hosey M.M. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, J. M. M. H. J. Biochemistry. 1996; 35: PubMed Scopus Google Scholar), was present in the C-terminal fragments isolated through in vitro of the α1C subunit. modified the of the fragments with the the α1C were in vitro in the or of cleaved with and to and with C that the C-terminal fragments of the α1C remained associated with the membrane either in the or of that of the C-terminal fragments of the not the of these to with the this does not the that may a in the of the C terminus with the of the with chymotrypsin was to the that associated with the The α1C either by of or by of was cleaved in vitro a of of the membrane and by with the C that the and α1C subunits were cleaved C-terminal fragments was the these were to to and the of the fragments remained associated with the the of kDa was present in the the C was the C terminus of the α1C the the for membrane was from the of the C-terminal fragments associated with the membrane present in the These results suggested that a for membrane of the C terminus was and of the α1C A the the of a with a of to the proline-rich domain (PRD) of J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The α1C PRD was and of the α1C subunit. a of as as a class SH3 The of this PRD to the membrane of the α1C C terminus was by to the PRD was to the of the α1C The or the PRD were with the in and to in vitro by of the membrane and the C that the C-terminal fragments from were in the membrane of generated the fragments of the C terminus as with the α1C the size of each was to the However, in to the α1C the C-terminal fragments of were present in in the the C-terminal generated from the α1C The C-terminal of was present in the membrane and in the fragments to be in the A of or C-terminal fragments from was in either or in the of These results the of the α1C PRD for the of the C terminus of the α1C with the membrane In the the PRD suggested that of C-terminal generated by chymotrypsin was in and the PRD for membrane was the PRD for membrane association. the α1C PRD serve as a for known SH3 C-terminal of the α1C were and with in The proteins and the PRD not The SH3 domains from Src, Lyn, Hck, and were as domain proteins bound to and to the proteins different of the α1C C terminus A and The of the α1C C-terminal proteins to the was and bound to the proteins to the proteins and to to the SH3 domains of Src, Lyn, and to the SH3 domains of and The in and of the C terminus, the the a protein the PRD of the α1C was generated for in the The α1C PRD bound the SH3 domains to about the as the C-terminal proteins it that the PRD of the α1C C terminus was to serve as a for known SH3 domains in to test SH3 domain that been identified in the β2 A.J. T. E. Hosey M.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google with the α1C A protein of the SH3 domain of the and was generated and in with the and the bound to the SH3 protein not In to the of the the α1C proteins and the a α1C PRD was to the to with the of the proteins to the of of the α1C PRD to the the of and to the protein These results that the PRD was for the the proteins and the of from the C terminus of α1C been to to in calcium channel currents A. E. E. L. J. Biol. Chem. Full Text PDF PubMed Google Scholar), that the C terminus of the full-length channel is to channel In to the PRD in this currents through as as through the was truncated at and ∼50 kDa of the C terminus. protein a as that of the ∼190-kDa truncated α1C that is isolated from native and to that produced by chymotrypsin were with the in and barium currents through the channels were with produced from α1C and In to for in of the different channel the for three were in and was in the of cells. In the of the α1C was that of the two α1C the of barium currents through channels either α1 at and at were in but from channels α1 subunits at These the results of A. E. E. L. J. Biol. Chem. Full Text PDF PubMed Google that the C terminus in channel In that the PRD of the full-length channel is for this of the C terminus of calcium channel α1 subunits in tissues and brain (1.De Jongh K.S. Warner C. Colvin A.A. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 10778-10782Crossref PubMed Scopus (122) Google Scholar, 2.Hell J.W. Yokoyama C.T. Wong S.T. Warner C. Snutch T.P. Catterall W.A. J. Biol. Chem. 1993; 268: 19451-19457Abstract Full Text PDF PubMed Google Scholar, 5.Gao T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar, Hosey M.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Hosey M.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). of the α1 is the proteolytic processing is a that in intact or that the proteins are While it remains to that of the α1 is not and previously that the processing of the α1C may not be the α1C is a protein A.J. R.E. Puri T.S. D. E. Hosey M.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, T.S. Gerhardstein B.L. Hosey M.M. Biochemistry. 1997; PubMed Scopus Google and does not the C-terminal that is in native that the to the α1C lack the or that participate in the to the 190-kDa the α1C is to a truncated form by from the be for of the native α1C the α1C is to proteolytic processing a 190-kDa form by a of and that proteolytic processing of this proteolytic have been to a of the full-length α1C from but of the in the of the full-length as the form of the protein T.S. The of L-type by of and Scholar). isolated were in the full-length form of α1C for of the α1C These with the of the of the C-terminal domain in intact by T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar), that of the α1C truncated 190-kDa form is not of but a processing in intact The proteolytic for the processing of the native and brain α1C subunits a been to the form of the α1C the short form in J.W. Westenbroek R.E. C. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar), the not appear to with the is is not in cells. However, a to been suggested to be in the processing and of proteins and may be present in J. L. W. M. Google Scholar, W. H. Google Scholar). of the full-length α1C to of not in the of the protein to the 190-kDa this that the proteolytic that is for the processing is a event. in of this from the that of α1C subunits in J.W. Westenbroek R.E. C. Catterall W.A. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar). In it is that the is this not been in the studies The fate of the C terminus of the α1C proteolytic processing is to as this domain is for different of channel function A. E. E. L. J. Biol. Chem. Full Text PDF PubMed Google Scholar), M. Y. L. E. Snutch T.P. 1995; PubMed Scopus Google Scholar, N. M. T. L. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Full Text Full Text PDF PubMed Scopus Google Scholar), and of the channel T. Y. E. N. 1996; PubMed Scopus Google Scholar, T. A. H. Green N. Hosey M.M. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). results obtained from immunofluorescence studies have that the C terminus of the α1C is present in intact and with the of the α1C and the T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). Two would these this that of the α1C protein present in intact is a full-length this is T. Puri T.S. Gerhardstein B.L. Chien A.J. Green R.D. Hosey M.M. J. Biol. Chem. 1997; 272: 19401-19407Abstract Full Text Full Text PDF PubMed Scopus (151) Google Scholar). The is that the C terminus of the α1C is processed in and remains associated with either the 190-kDa of the channel or membrane in of this is that the C-terminal generated processing of the were fragments that remained associated with the The that the α1C PRD was for the membrane of the C-terminal the by cleaved C-terminal α1C fragments functionally associated with the While it is not known the of the C-terminal fragments with the the fragments be to the 190-kDa truncated α1C or to membrane or The that the α1C PRD to known SH3 domains that be SH3 domain the SH3 domains from the Src, Lyn, and as for the α1C PRD was not the of homology the and the PRD from J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The PRD from to domain proteins from Src and but not or J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). the that the α1C PRD may function to the channel to protein that may be in the of channel In this been to the of L-type channels J. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, S. T. D. J. J. PubMed Google Scholar), and this the of the channels with a kinase in the that the of the α1C may be by Src and that may be a of the Src protein with the calcium channel N. D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The PRD is in the α1C identified in M. E. W. PubMed Scopus Google Scholar), and the PRD from this α1C may with the SH3 domain of While most of the α1 isoforms the of C of the α1 subunits the class domain in the α1C subunit. However, studies have that a proline-rich domain in the C terminus of to SH3 domain in protein in A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In the the α1D isoforms have and to to be in the PRD J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). are to test the that these α1 subunits to SH3 The that the domain bound to the α1C PRD suggested that the of the domain with the α1C PRD may be for channel and the the domain and the PRD from the α1C is not for the of the α1C C terminus with the membrane as in the in vitro the α1C C-terminal fragments generated by chymotrypsin were associated with the membrane of or not the β2 was A for the PRD remains to be was the that the of either the PRD or of the C terminus in increased channel studies that at and of the C terminus of rise to currents that were currents through α1C A. E. E. L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). generated by and were a for the PRD and the of the C terminus in the function of the C terminus. be of to the of C-terminal domains with truncated α1C as channel that the C-terminal fragments would currents obtained with a as it is that the C terminus is to channel function in it be to the C terminus to to the The PRD may not the but these participate in the of the PRD in increased channel it may either of domain that channel currents or be in the domain to the channel with SH3 domain The results the for the hypothesis that the C-terminal domain of the α1C may be cleaved but functionally associated with the calcium a of channel of the C terminus or of the PRD of the α1C have been to for increased channel it is that the C-terminal a to the of inhibition by the of the C-terminal domain with the of this In the identified for at the C terminus, in of the it is that at to the of the C-terminal domain with The of the function of the processing of the C terminus of α1 subunits of calcium channels the that this domain is to in channel