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ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit.

ABSTRACT: Membrane proteins impose enormous challenges to cellular protein homeostasis during their post-translational targeting, and they require chaperones to keep them soluble and translocation competent. Here we show that a novel targeting factor in the chloroplast signal recognition particle (cpSRP), cpSRP43, is a highly specific molecular chaperone that efficiently reverses the aggregation of its substrate proteins. In contrast to 'ATPases associated with various cellular activities' (AAA(+)) chaperones, cpSRP43 uses specific binding interactions with its substrate to mediate its 'disaggregase' activity. This disaggregase capability can allow targeting machineries to more effectively capture their protein substrates and emphasizes a close connection between protein folding and trafficking processes. Moreover, cpSRP43 provides the first example to our knowledge of an ATP-independent disaggregase and shows that efficient reversal of protein aggregation can be attained by specific binding interactions between a chaperone and its substrate.

SUBMITTER: Jaru-Ampornpan P

PROVIDER: S-EPMC2917185 | biostudies-literature | 2010 Jun

REPOSITORIES: biostudies-literature

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ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit.

Jaru-Ampornpan Peera P Shen Kuang K Lam Vinh Q VQ Ali Mona M Doniach Sebastian S Jia Tony Z TZ Shan Shu-Ou SO

Nature structural & molecular biology 20100427 6

Membrane proteins impose enormous challenges to cellular protein homeostasis during their post-translational targeting, and they require chaperones to keep them soluble and translocation competent. Here we show that a novel targeting factor in the chloroplast signal recognition particle (cpSRP), cpSRP43, is a highly specific molecular chaperone that efficiently reverses the aggregation of its substrate proteins. In contrast to 'ATPases associated with various cellular activities' (AAA(+)) chaper ...[more]

PMID: 20424608

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Project description:Virulence properties of cariogenic Streptococcus mutans depend on integral membrane proteins. Bacterial cotranslational protein trafficking involves the signal recognition particle (SRP) pathway components Ffh and FtsY, the SecYEG translocon, and YidC chaperone/insertases. Unlike Escherichia coli, S. mutans survives loss of the SRP pathway and has two yidC paralogs. This study characterized YidC1 and YidC2 interactomes to clarify respective functions alone and in concert with the SRP and/or Sec translocon. Western blots of formaldehyde cross-linked or untreated S. mutans lysates were reacted with anti-Ffh, anti-FtsY, anti-YidC1, or anti-YidC2 antibodies followed by mass spectrometry (MS) analysis of gel-shifted bands. Cross-linked lysates of wild-type and ΔyidC2 strains were reacted with anti-YidC2-coupled Dynabeads, and cocaptured proteins were identified by MS. Last, YidC1 and YidC2 C-terminal tail-captured proteins were subjected to two-dimensional (2D) difference gel electrophoresis and MS analysis. Direct interactions of putative YidC1 and YidC2 binding partners were confirmed by bacterial two-hybrid assay. Our results suggest YidC2 works preferentially with the SRP pathway, while YidC1 is preferred for SRP-independent Sec translocon-mediated translocation. YidC1 and YidC2 autonomous pathways were also apparent. Two-hybrid assay identified interactions between holotranslocon components SecYEG/YajC and YidC1. Both YidC1 and YidC2 interacted with Ffh, FtsY, and chaperones DnaK and RopA. Putative membrane-localized substrates HlyX, LemA, and SMU_591c interacted with both YidC1 and YidC2. Identification of several Rgp proteins in the YidC1 interactome suggested its involvement in bacitracin resistance, which was decreased in ΔyidC1 and SRP-deficient mutants. Collectively, YidC1 and YidC2 interactome analyses has further distinguished these paralogs in the Gram-positive bacterium S. mutans IMPORTANCE Streptococcus mutans is a prevalent oral pathogen and major causative agent of tooth decay. Many proteins that enable this bacterium to thrive in its environmental niche and cause disease are embedded in its cytoplasmic membrane. The machinery that transports proteins into bacterial membranes differs between Gram-negative and Gram-positive organisms, an important difference being the presence of multiple YidC paralogs in Gram-positive bacteria. Characterization of a protein's interactome can help define its physiological role. Herein, we characterized the interactomes of S. mutans YidC1 and YidC2. Results demonstrated substantial overlap between their interactomes but also revealed several differences in their direct protein binding partners. Membrane transport machinery components were identified in the context of a large network of proteins involved in replication, transcription, translation, and cell division/cell shape. This information contributes to our understanding of protein transport in Gram-positive bacteria in general and informs our understanding of S. mutans pathogenesis.

Dataset Information

ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit.

Publications

ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit.

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