Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 293, Issue 23, Pages 8861-8873Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.RA118.002215
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Funding
- Betty and Gordon Moore Foundation [94-3397785]
- National Institutes of Health [R01 GM114390, 2 T32 GM 7616-36]
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Integral membrane proteins are prone to aggregation and misfolding in aqueous environments and therefore require binding by molecular chaperones during their biogenesis. Chloroplast signal recognition particle 43 (cpSRP43) is an ATP-independent chaperone required for the biogenesis of the most abundant class of membrane proteins, the light-harvesting chlorophyll a/b-binding proteins (LHCPs). Previous work has shown that cpSRP43 specifically recognizes an L18 loop sequence conserved amongLHCPparalogs. However, howcpSRP43 protects the transmembrane domains (TMDs) of LHCP from aggregation was unclear. In this work, alkylation-protection and site-specific cross-linking experiments found that cpSRP43 makes extensive contacts with all the TMDs in LHCP. Site-directed mutagenesis identified a class of cpSRP43 mutants that bind tightly to the L18 sequence but are defective in chaperoning full-length LHCP. These mutations mapped to hydrophobic surfaces on or near the bridging helix and the beta-hairpins lining the ankyrin repeat motifs of cpSRP43, suggesting that these regions are potential sites for interaction with the client TMDs. Our results suggest a working model for client protein interactions in this membrane protein chaperone.
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