Single methyl groups can act as toggle switches to specify transmembrane Protein-protein interactions.

Li He,Daniel DiMaio,Birthe B Kragelund,Emily B Cohen,Ashish Shelar,Gevorg Grigoryan,Erin N Heim,Helena Steinocher

doi:10.7554/elife.27701

Li He, Daniel DiMaio + Show 6 more

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https://doi.org/10.7554/elife.27701

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Abstract

Transmembrane domains (TMDs) engage in protein-protein interactions that regulate many cellular processes, but the rules governing the specificity of these interactions are poorly understood. To discover these principles, we analyzed 26-residue model transmembrane proteins consisting exclusively of leucine and isoleucine (called LIL traptamers) that specifically activate the erythropoietin receptor (EPOR) in mouse cells to confer growth factor independence. We discovered that the placement of a single side chain methyl group at specific positions in a traptamer determined whether it associated productively with the TMD of the human EPOR, the mouse EPOR, or both receptors. Association of the traptamers with the EPOR induced EPOR oligomerization in an orientation that stimulated receptor activity. These results highlight the high intrinsic specificity of TMD interactions, demonstrate that a single methyl group can dictate specificity, and define the minimal chemical difference that can modulate the specificity of TMD interactions and the activity of transmembrane proteins.

Highlights

Specific interactions between proteins underlie much of biology
By studying simple model TM proteins, we discovered that interactions between TM domains (TMDs) can display high specificity in mammalian cells that can be precisely modulated by minimal structural differences in the interacting helices
We discovered that single leucine-isoleucine substitutions at two positions in a traptamer, which change the placement of single methyl groups, determined whether it bound and activated the human erythropoietin receptor (hEPOR), the mouse EPOR (mEPOR), or both receptors

Summary

Introduction

Specific interactions between proteins underlie much of biology. Proteomics analysis has identified thousands of protein-protein interactions (e.g., [Bork et al, 2004]), but in most cases the molecular basis for the ability of a protein to bind to specific protein partners but not to closely related proteins is poorly understood. In multi-pass TM proteins, which span the membrane multiple times, TMDs interact to properly fold the protein into a functional state within the bilayer. For single-pass TM proteins, TMDs have traditionally been viewed as primarily serving to anchor the protein into the lipid bilayer, but they can engage in highly specific intermolecular protein-protein interactions that regulate protein oligomerization and activity (Langosch and Arkin, 2009; Moore et al, 2008). TMDs can align laterally in the membrane and oligomerize via hydrogen bonds, salt-bridges, or van der Waals packing interactions (Langosch and Arkin, 2009; Moore et al, 2008; Bugge et al, 2016; Choma et al, 2000; Zhou et al, 2000). The analysis of TMD complexes has been hindered by the difficulties in obtaining high-resolution structures of protein segments that cross membranes (Bugge et al, 2016)

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