Intrinsic membrane association of Drosophila cysteine string proteins

FEBS Letters

Whitelegge, Julian P¹  Kohan, Sirus A¹  Gundersen, Cameron B¹  Mastrogiacomo, Alessandro¹ 

[1] Department of Molecular and Medical Pharmacology and Crump Institute for Biological Imaging, UCLA School of Medicine, Los Angeles, CA 90095, USA

关键词: Cysteine string protein;    Membrane protein;    Protein fatty acylation;    Synaptic vesicle;    Nerve terminal;   

DOI  :  10.1016/S0014-5793(98)01092-8

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Cysteine string proteins (csps) are highly conserved constituents of vertebrate and invertebrate secretory organelles. Biochemical and immunoprecipitation experiments implied that vertebrate csps were integral membrane proteins that were tethered to the outer leaflet of secretory vesicles via the fatty acyl residues of their extensively acylated cysteine string. Independently, work of others suggested that Drosophila csps were peripheral membrane proteins that were anchored to membranes by a mechanism that was independent of the cysteine string and its fatty acyl residues. We extended these investigation and found first that sodium carbonate treatment partially stripped both csps and the integral membrane protein, synaptotagmin, from Drosophila membranes. Concomitantly, carbonate released fatty acids into the medium, arguing that it has a mild, solubilizing effect on these membranes. Second, we observed that Drosophila csps behaved like integral membrane proteins in Triton X-114 partitioning experiments. Third, we found that when membrane-bound csps were deacylated, they remained membrane bound. Moreover, it appeared that hydrophobic interactions were necessary for this persistent membrane association of csps. Thus, neither reducing conditions, urea, nor chaotropic agents displaced deacylated csps from membranes. Only detergents were effective in solubilizing deacylated csps. Finally, by virtue of the inaccessibility of deacylated csps to thiol alkylation by the membrane-impermeant alkylating reagent, iodoacetic acid, we inferred that it was the cysteine string domain that mediated the membrane association of deacylated csps. Thus, we conclude that under physiological conditions csps are integral membrane proteins of secretory organelles, and that the cysteine string domain plays a vital role in the membrane association of these proteins.

【 授权许可】

Unknown