A MUB E2 structure reveals E1 selectivity between cognate ubiquitin E2s in eukaryotes.

Xiaolong Lu,Caitlin C Brenner,Olga Koroleva,Brian P Downes,Konstantin R Malley,Sergey Korolev

doi:10.1038/ncomms12580

Xiaolong Lu, Caitlin C Brenner + Show 4 more

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https://doi.org/10.1038/ncomms12580

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Abstract

Ubiquitin (Ub) is a protein modifier that controls processes ranging from protein degradation to endocytosis, but early-acting regulators of the three-enzyme ubiquitylation cascade are unknown. Here we report that the prenylated membrane-anchored ubiquitin-fold protein (MUB) is an early-acting regulator of subfamily-specific E2 activation. An AtMUB3:AtUBC8 co-crystal structure defines how MUBs inhibit E2∼Ub formation using a combination of E2 backside binding and a MUB-unique lap-bar loop to block E1 access. Since MUBs tether Arabidopsis group VI E2 enzymes (related to HsUbe2D and ScUbc4/5) to the plasma membrane, and inhibit E2 activation at physiological concentrations, they should function as potent plasma membrane localized regulators of Ub chain synthesis in eukaryotes. Our findings define a biochemical function for MUB, a family of highly conserved Ub-fold proteins, and provide an example of selective activation between cognate Ub E2s, previously thought to be constitutively activated by E1s.

Highlights

Ubiquitin (Ub) is a protein modifier that controls processes ranging from protein degradation to endocytosis, but early-acting regulators of the three-enzyme ubiquitylation cascade are unknown
It was previously reported that membrane-anchored ubiquitin-fold protein (MUB) function as plasma membrane (PM) adaptors for an E2 subfamily, but here, the analysis reveals that MUBs inhibit activation of these critical Ub E2s
Ser[22] on the backside binding site (BBS) of AtUBC8 is distant from the active-site Cys[85], and was previously determined to interfere with MUB binding[30]

Summary

Introduction

Ubiquitin (Ub) is a protein modifier that controls processes ranging from protein degradation to endocytosis, but early-acting regulators of the three-enzyme ubiquitylation cascade are unknown. Current models suggest the E1 UFD first interacts with the E2 in a distal conformation before rotating towards the opposed Cys domain to form a proximal configuration, placing the E1 and E2 active sites in range for Ub transfer[9] (Fig. 1). This elegant mechanism affords regulation potential, which is used between Ub-like protein tags (Ubls), but not traditionally within a Ubl family. Ube2D3 and the SUMO E2 Ubc[9] use the BBS to interact with Ub or SUMO, to enhance chain elongation[23,24], the BBS of Rad[6] promotes Ub

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