Human Suv3 protein reveals its unique features among SF2 helicases

Abstract

Suv3 is a helicase involved in efficient turnover and surveillance of RNA in eukaryotes. In vitro study shows that human Suv3 (hSuv3) in complex with human polynucleotide phosphorylase has RNA degradosome activity. The enzyme is mainly localized in mitochondria; but small fractions are found in cell nuclei. Here we present two X-ray crystallographic structures of human Suv3 in complex with AMPPNP, a non-hydrolysable analog of ATP, and with a short five-nucleotide strand of RNA, at a resolution of 2.08 and 2.9 Å, respectively. The structure of the enzyme is very similar in the two complexes and consists of four domains. Two RecA-like domains form a tandem typical for all helicases from the SF2 superfamily which, together with the C-terminal all-helix domain, makes a ring structure through which the nucleotide strand threads. The N-terminal, mostly helical, domain is positioned externally with respect to the core of the enzyme. Most of the typical helicase motifs are present in hSuv3, but the protein shows certain unique characteristics, suggesting that Suv3 enzymes may constitute a separate subfamily of helicases.