Structural basis of 7SK RNA 5'-γ-phosphate methylation and retention by MePCE.

Publication Type:

Journal Article

Source:

Nat Chem Biol, Volume 15, Issue 2, p.132-140 (2019)

Abstract:

<p>Among RNA 5&#39;-cap structures, γ-phosphate monomethylation is unique to a small subset of noncoding RNAs, 7SK and U6 in humans. 7SK is capped by methylphosphate capping enzyme (MePCE), which has a second nonenzymatic role as a core component of the 7SK ribonuclear protein (RNP), an essential regulator of RNA transcription. We report 2.0- and 2.1-Å X-ray crystal structures of the human MePCE methyltransferase domain bound to S-adenosylhomocysteine (SAH) and uncapped or capped 7SK substrates, respectively. 7SK recognition is achieved by protein contacts to a 5&#39;-hairpin-single-stranded RNA region, thus explaining MePCE&#39;s specificity for 7SK and U6. The structures reveal SAH and product RNA in a near-transition-state geometry. Unexpectedly, binding experiments showed that MePCE has higher affinity for capped versus uncapped 7SK, and kinetic data support a model of slow product release. This work reveals the molecular mechanism of methyl transfer and 7SK retention by MePCE for subsequent assembly of 7SK RNP.</p>

PDB: 
6DCB (MePCE–SAH–7SK) and 6DCC (MePCE–SAH–me7SK)
Detector: 
PILATUS
Beamline: 
24-ID-C