Ligases;
Forming phosphoric-ester bonds;
Ligases that form phosphoric-ester bonds (only sub-subclass identified to date)
BRITE hierarchy

RNA-3'-phosphate:RNA ligase (cyclizing, GMP-forming)

GTP + [RNA]-3'-(3'-phospho-ribonucleoside) = GMP + diphosphate + [RNA]-3'-(2',3'-cyclophospho)-ribonucleoside (overall reaction) [RN:R10537];
(1a) GTP + [RNA 3'-phosphate cyclase]-L-histidine = 5'-guanosyl [RNA 3'-phosphate cyclase]-Ntau-phosphono-L-histidine + diphosphate;
(1b) 5'-guanosyl [RNA 3'-phosphate cyclase]-Ntau-phosphono-L-histidine + [RNA]-3'-(3'-phospho-ribonucleoside) = [RNA 3'-phosphate cyclase]-L-histidine + [RNA]-3'-ribonucleoside-3'-(5'-diphosphoguanosine);
(1c) [RNA]-3'-ribonucleoside-3'-(5'-diphosphoguanosine) = [RNA]-3'-(2',3'-cyclophospho)-ribonucleoside + GMP

R10537
Reaction

GTP [CPD:C00044];
[RNA]-3'-(3'-phospho-ribonucleoside);
[RNA 3'-phosphate cyclase]-L-histidine;
5'-guanosyl [RNA 3'-phosphate cyclase]-Ntau-phosphono-L-histidine;
[RNA]-3'-ribonucleoside-3'-(5'-diphosphoguanosine)

The enzyme, which is specific for GTP, was characterized from the archaeon Pyrococcus furiosus. The enzyme converts the 3'-terminal phosphate of various RNA substrates into the 2',3'-cyclic phosphodiester in a GTP-dependent reaction. Catalysis occurs by a three-step mechanism, starting with the activation of the enzyme by GTP, forming a phosphoramide bond between guanylate and a histidine residue. The guanylate group is then transferred to the 3'-phosphate terminus of the substrate, forming the capped structure [RNA]-3'-(5'-diphosphoguanosine). Finally, the enzyme catalyses an attack of the vicinal O-2' on the 3'-phosphorus, which results in formation of cyclic phosphate and release of the guanylate. cf. EC 6.5.1.4, RNA 3'-terminal-phosphate cyclase (ATP).

EC 6.5.1.5 created 2013, modified 2016

1  [PMID:22074260]