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bioRxiv · 10.1101/2020.07.05.188557

The ER membrane chaperone Shr3 co-translationally assists biogenesis of related plasma membrane transport proteins

Ring, A.·Myronidi, I.·Ljungdahl, P. O.
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Abstract

Proteins with multiple membrane-spanning segments (MS) co-translationally insert into the endoplasmic reticulum (ER) membrane of eukaryotic cells. In Saccharomyces cerevisiae, Shr3 is an ER membrane-localized chaperone that is specifically required for the functional expression of amino acid permeases (AAP), a family of eighteen transporters comprised of 12 MS. Here, comprehensive scanning mutagenesis and deletion analysis of Shr3, combined with a modified split-ubiquitin approach, were used to probe chaperone-substrate interactions with seven different AAP in vivo. Our findings indicate that Shr3 specifically recognizes AAP substrates, largely independent of sequence-specific interactions involving membrane and luminally oriented domains. Shr3 selectively and robustly interacts with nested C-terminal AAP truncations in marked contrast to similar truncations of non-Shr3 substrate polytopic sugar transporters. Strikingly, Shr3-AAP interactions initiate with the first 4 MS of AAP and successively strengthen, but abruptly weaken when all 12 MS are present. The data are consistent with Shr3 acting in a temporal manner as a scaffold preventing AAP translation intermediates from engaging in non-productive interactions.

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Ring, A., Myronidi, I., Ljungdahl, P. O.. 2020-07-05. The ER membrane chaperone Shr3 co-translationally assists biogenesis of related plasma membrane transport proteins. https://doi.org/10.1101/2020.07.05.188557

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