Transmembrane Serine of Rot1 protein is essential for yeast cell viability

Polar residues are present in transmembrane (TM) helices and may influence the folding or association of membrane proteins. Here, we use an in vivo approach to analyse the functional or structural role of amino acid residues in membrane-spanning motifs using Rot1 protein as a model. Rot1 is an essential membrane protein in Saccharomyces cerevisiae and contains a single TM domain. An Ala-insertion scanning analysis of this TM helix revealed that the integrity of the central domain is essential for protein function. We identified a critical Ser residue inside the helix that plays an essential role in maintaining cell viability in budding yeast. Replacement of the Ser residue at position 250 by a broad variety of amino acid residues did not affect protein targeting and location, but completely disrupted protein function, causing cell death. Interestingly, substitution of the Ser residue by Thr resulted in sustained cell viability, demonstrating that the hydroxyl group of the TM Ser side chain plays a critical role in protein function. These results indicate that Rot1 needs the TM Ser250 to interact with other membrane components and exert its functional role, avoiding exposure of the Ser hydrogen bonding group at the lipid-exposed surface.

Source: BJ Cell - December 5, 2013 Category: Biochemistry Authors: C A. Martínez-Garay, M Juanes, J Igual, I Mingarro, M Bañó Tags: BJ Biomolecules Source Type: research