Palmitoylation and membrane interactions of the neuroprotective chaperone cysteine-string protein.
Cysteine-string protein (CSP) is an extensively palmitoylated DnaJ-family chaperone, which exerts an important neuroprotective function. Palmitoylation is required for the intracellular sorting and function of CSP, and thus it is important to understand how this essential modification of CSP is regulated. Recent work identified 23 putative palmitoyl transferases containing a conserved DHHC domain in mammalian cells, and here we show that palmitoylation of CSP is enhanced specifically by co-expression of the Golgi-localized palmitoyl transferases DHHC3, DHHC7, DHHC15, or DHHC17. Indeed, these DHHC proteins promote stable membrane attachment of CSP, which is otherwise cytosolic. An inverse correlation was identified between membrane affinity of unpalmitoylated CSP mutants and subsequent palmitoylation: mutants with an increased membrane affinity localize to the endoplasmic reticulum (ER) and are physically separated from the Golgi-localized DHHC proteins. Palmitoylation of an ER-localized mutant could be rescued by brefeldin A treatment, which promotes the mixing of ER and Golgi membranes. Interestingly though, the palmitoylated mutant remained at the ER following brefeldin A washout and did not traffic to more distal membrane compartments. We propose that CSP has a weak membrane affinity that allows the protein to locate its partner Golgi-localized DHHC proteins directly by membrane "sampling." Mutations that enhance membrane association prevent sampling and lead to accumulation of CSP on cellular membranes such as the ER. The coupling of CSP palmitoylation to Golgi membranes may thus be an important requirement for subsequent sorting.
Greaves
Jennifer
J
Centre for Integrative Physiology, School of Biomedical Sciences, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom.
Salaun
Christine
C
Fukata
Yuko
Y
Fukata
Masaki
M
Chamberlain
Luke H
LH
D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D054878:Lipoylation / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D018696:Neuroprotective Agents / Q000378:metabolism; D016716:PC12 Cells; D017434:Protein Structure, Tertiary / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats
D050956:HSP40 Heat-Shock Proteins; D008565:Membrane Proteins; D018696:Neuroprotective Agents; D011500:Protein Synthesis Inhibitors; C088460:cysteine string protein; D020126:Brefeldin A; D000217:Acyltransferases; C574550:ZDHHC3 protein, human