Cysteine-string protein isoform beta (Cspbeta) is targeted to the trans-Golgi network as a non-palmitoylated CSP in clonal beta-cells.
Cysteine string proteins (CSPs) belong to the DnaJ-like chaperone family and play an important role in regulated exocytosis in neurons and endocrine cells. The palmitoylation of several residues in a cysteine string domain may anchor CSPs to the exocytotic vesicle surface and in pancreatic beta-cells, Cspalpha is localized on insulin containing large dense core vesicles (LDCVs). An isoform closely related to Cspalpha, Cspbeta, has been obtained from testis cell cDNA libraries. To gain insights on this isoform and more generally on the properties of CSPs, we compared Cspalpha and Cspbeta. In pull-down experiments, Cspbeta was able to interact to the same extent with two of the known Cspalpha chaperone partners, Hsc70 and SGT. Upon transient overexpression in clonal beta-cells, Cspbeta but not Cspalpha was mainly produced as a non-palmitoylated protein and mutational analysis indicated that domains distinct from the cysteine string are responsible for this difference. As Cspbeta remained tightly bound to membranes, intrinsic properties of CSPs are sufficient for interactions with membranes. Indeed, recombinant Cspalpha and Cspbeta were capable to interact with membranes even in their non-palmitoylated forms. Furthermore, overexpressed Cspbeta was not associated with LDCVs, but was localized at the trans-Golgi network. Our results suggest a possible correlation between the specific membrane targeting and the palmitoylation level of CSPs.
Boal
Frédéric
F
Institut Européen de Chimie et Biologie, Pôle Biologie Cellulaire et Moléculaire, JE 2390, F-33607 Pessac, France.
Le Pevelen
Séverine
S
Cziepluch
Celina
C
Scotti
Pier
P
Lang
Jochen
J
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002999:Clone Cells / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D019308:Palmitic Acid / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism*
D002352:Carrier Proteins; D018076:DNA, Complementary; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D011994:Recombinant Proteins; C088460:cysteine string protein; D019308:Palmitic Acid