BMERB domains are bivalent Rab8 family effectors evolved by gene duplication.

Amrita Rai,Anastasia Oprisko,Aymelt Itzen,Matthias P Müller,Jeremy Campos,Emerich Mihai Gazdag,Roger S Goody,Yangxue Fu,Timon Friese

doi:10.7554/elife.18675

Amrita Rai, Anastasia Oprisko + Show 7 more

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https://doi.org/10.7554/elife.18675

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Abstract

In their active GTP-bound form, Rab proteins interact with proteins termed effector molecules. In this study, we have thoroughly characterized a Rab effector domain that is present in proteins of the Mical and EHBP families, both known to act in endosomal trafficking. Within our study, we show that these effectors display a preference for Rab8 family proteins (Rab8, 10, 13 and 15) and that some of the effector domains can bind two Rab proteins via separate binding sites. Structural analysis allowed us to explain the specificity towards Rab8 family members and the presence of two similar Rab binding sites that must have evolved via gene duplication. This study is the first to thoroughly characterize a Rab effector protein that contains two separate Rab binding sites within a single domain, allowing Micals and EHBPs to bind two Rabs simultaneously, thus suggesting previously unknown functions of these effector molecules in endosomal trafficking.

Highlights

Rab proteins, the biggest subfamily within the superfamily of small GTPases, are major regulators of vesicular trafficking in eukaryotic cells (Takai et al, 2001)
We set out to systematically confirm and quantify the interaction of 5 of these Rab proteins with the bivalent Mical/ EHBP Rab binding” (bMERB) domains of Mical-1, Mical-3, Mical-cL, EHBP1 and EHBP1L1 via analytical size exclusion chromatography
We present a thorough biochemical and structural analysis of a Rab effector domain termed bivalent Mical/EHBP Rab binding domain

Summary

Introduction

The biggest subfamily within the superfamily of small GTPases, are major regulators of vesicular trafficking in eukaryotic cells (Takai et al, 2001). In long-distance vesicular transport processes (e.g. in neuronal axons and dendrites), directed vesicular transport along cytoskeletal tracks appears to be an obvious mechanism and, consistently, different effector proteins have been reported to link Rab proteins to the cytoskeleton (Kevenaar and Hoogenraad, 2015; Horgan and McCaffrey, 2011). One such family of effector proteins that was reported to link Rab proteins and the cytoskeleton is the Mical (molecules interacting with CasL) family (Figure 1) (Fischer et al, 2005). All except Mical-2 contain a C-terminal coiled-coil domain

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