Intrinsic membrane association of Drosophila cysteine string proteins.
FEBS Lett
; 436(1): 85-91, 1998 Sep 25.
Article
de En
| MEDLINE
| ID: mdl-9771899
ABSTRACT
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.
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Collection:
01-internacional
Base de données:
MEDLINE
Sujet principal:
Protéines de liaison au calcium
/
Protéines d'insecte
/
Drosophila melanogaster
/
Protéines membranaires
/
Protéines de tissu nerveux
Type d'étude:
Risk_factors_studies
Limites:
Animals
Langue:
En
Journal:
FEBS Lett
Année:
1998
Type de document:
Article
Pays d'affiliation:
États-Unis d'Amérique