Structural insights into the molecular mechanism of the m(6)A writer complex.

Paweł Śledź,Martin Jinek

doi:10.7554/elife.18434

Abstract

Methylation of adenosines at the N(6) position (m(6)A) is a dynamic and abundant epitranscriptomic mark that regulates critical aspects of eukaryotic RNA metabolism in numerous biological processes. The RNA methyltransferases METTL3 and METTL14 are components of a multisubunit m(6)A writer complex whose enzymatic activity is substantially higher than the activities of METTL3 or METTL14 alone. The molecular mechanism underpinning this synergistic effect is poorly understood. Here we report the crystal structure of the catalytic core of the human m(6)A writer complex comprising METTL3 and METTL14. The structure reveals the heterodimeric architecture of the complex and donor substrate binding by METTL3. Structure-guided mutagenesis indicates that METTL3 is the catalytic subunit of the complex, whereas METTL14 has a degenerate active site and plays non-catalytic roles in maintaining complex integrity and substrate RNA binding. These studies illuminate the molecular mechanism and evolutionary history of eukaryotic m(6)A modification in post-transcriptional genome regulation.

Highlights

Methylation of the amino group at the N6 position in adenine nucleobases (m6A) has emerged as a dynamic posttranscriptional RNA modification (Fu et al, 2014; Liu and Pan, 2016; Meyer and Jaffrey, 2014; Yue et al, 2015)
Previous studies have shown that METTL3 and METTL14 physically interact with each other and that their association has a synergistic effect on the catalytic activity of the complex (Liu et al, 2014)
To identify protein constructs amenable to crystallization, the full-length METTL3METTL14 complex was subjected to limited proteolysis with chymotrypsin and N-terminal sequencing

Summary

Introduction

Methylation of the amino group at the N6 position in adenine nucleobases (m6A) has emerged as a dynamic posttranscriptional RNA modification (Fu et al, 2014; Liu and Pan, 2016; Meyer and Jaffrey, 2014; Yue et al, 2015). As the most abundant internal modification in eukaryotic messenger and long non-coding RNAs (Dominissini et al, 2013; Meyer et al, 2012), m6A has been shown to regulate the processing (Alarcon et al, 2015b; Xiao et al, 2016), translation (Lin et al, 2016; Wang et al, 2015) and stability (Wang et al, 2014a) of cellular transcripts. The nuclear YTHDC1 protein modulates pre-mRNA splicing by recruiting and modulating splicing factors (Xiao et al, 2016) Another m6A reader, HNRNPA2B1, has been shown to promote pri-microRNA processing through interactions with the Microprocessor complex (Alarcon et al, 2015a)

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Conclusion