Phosphatase Subfamily RNGTT

Phosphatase Classification: Fold CC1: Superfamily CC1: Family DSP: Subfamily RNGTT

RNGTT is an mRNA capping enzyme found in holozoa.

Evolution

RNGTT is ubiquitous in holozoa, usually as a single-copy gene. As described in below, RNGTT has two distinct enzymatic domains: RNA triphosphatase and guanylyltransferase (GTase). In fungi, the two enzymatic activities are contained in separate but necessarily interacting proteins [1]. The GTase is conserved across eukaryotes; The phosphatase is found across eukaryotes including plants except fungi. Fungi have unique RNA triphosphatase distinct from that of RNGTT in other clades in sequence and structure [2, 3]. Thus, RNGTT emerged in early eukaryotes but lost in fungi perhaps through gene fission.

Domain

Holozoan RNGTT has three conserved regions: N-terminal phosphatase domain removing the gamma phosphate, a guanylyltransferase (GTase) domain that adds GMP (mRNA_cap_enzyme), and C-terminal conserved region (mRNA_cap_C). Monosiga has a divergent RNGTT-like phosphatases (RNGTT-2) which lacks the GTase and C-terminal region, but has an N-terminal AB-hydolase domain, and this domain architecture is also seen in many fungi (e.g. Candida albicans KGU18713.1, Rhizopus microsporus EI89000.1), and in Caspaspora (XP_004364216.2), and is similar to an algal protein that encodes only the phosphatase domain (e.g. Volvox carteri XP_002954283.1).

Function

RNGTT is an mRNA capping enzyme. Capping of nascent RNA 5′ ends is accomplished in eukaryotic cells and for most viruses in three sequential catalytic steps: removal of the gamma phosphate by RNA triphosphatase (RTase), addition of GMP from GTP by guanylyltransferase (GTase) via a phosphoamide linked GMP–enzyme intermediate, and N7 methylation of the added GMP by RNA (guanine-N7) methyltransferase (MTase) [3]. RNGTT carries out the first two steps through its phosphatase domain (RTase) and GTase domain.

References

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