Crystal structure of small RNA methyltransferase HEN1
Classification:
TRANSFERASE/RNA
Technique:
X-Ray Diffraction
Resolution:
3.1
R value free:
0.288
R value observed:
0.26
R value work:
0.26
Abstract of the PDB Structure's related Publication:
RNA silencing is a conserved regulatory mechanism in fungi, plants and animals that regulates gene expression and defence against viruses and transgenes. Small silencing RNAs of approximately 20-30 nucleotides and their associated effector proteins, the Argonaute family proteins, are the central components in RNA silencing. A subset of small RNAs, such as microRNAs and small interfering RNAs (siRNAs) in plants, Piwi-interacting RNAs in animals and siRNAs in Drosophila, requires an additional crucial step for their maturation; that is, 2'-O-methylation on the 3' terminal nucleotide. A conserved S-adenosyl-l-methionine-dependent RNA methyltransferase, HUA ENHANCER 1 (HEN1), and its homologues are responsible for this specific modification. Here we report the 3.1 A crystal structure of full-length HEN1 from Arabidopsis in complex with a 22-nucleotide small RNA duplex and cofactor product S-adenosyl-l-homocysteine. Highly cooperative recognition of the small RNA substrate by multiple RNA binding domains and the methyltransferase domain in HEN1 measures the length of the RNA duplex and determines the substrate specificity. Metal ion coordination by both 2' and 3' hydroxyls on the 3'-terminal nucleotide and four invariant residues in the active site of the methyltransferase domain suggests a novel Mg(2+)-dependent 2'-O-methylation mechanism.
HEN1 deposits the methyl group on to the 2' OH of the 3' terminal nucleotide in double stranded small RNAs. It is a step in miRNA and siRNA metabolism. The modification prevents the 3' uridylation and degradation of the RNA molecule. AdoMet is a methyl group donor. Animal homologue of Hen1 modifies piRNA and is important for germ cell development.
Kinetic and functional analysis of the small RNA methyltransferase HEN1: the catalytic domain is essential for preferential modification of duplex RNA.
HEN1 recognizes 21-24 nt small RNA duplexes and deposits a methyl group onto the 2' OH of the 3' terminal nucleotide.
Kinetic and functional analysis of the small RNA methyltransferase HEN1: the catalytic domain is essential for preferential modification of duplex RNA.
Mechanistic insights into small RNA recognition and modification by the HEN1 methyltransferase.
Methylation as a crucial step in plant microRNA biogenesis.
Methylation protects miRNAs and siRNAs from a 3'-end uridylation activity in Arabidopsis.
Molecular phylogenetics and comparative modeling of HEN1, a methyltransferase involved in plant microRNA biogenesis.
siRNAs compete with miRNAs for methylation by HEN1 in Arabidopsis.
Structural insights into mechanisms of the small RNA methyltransferase HEN1.