Functional investigation of a gene encoding pteridine glycosyltransferase for cyanopterin synthesis in Synechocystis sp. PCC 6803.

A gene (slr1166) putatively encoding pteridine glycosyltransferase was disrupted with a kanamycin resistance cassette in Synechocystis sp. PCC 6803, which produces cyanopterin. The deduced polypeptide from slr1166 consisted of 354 amino acid residues sharing 45% sequence identity with UDP-glucose:tetrahydrobiopterin alpha-glucosyltransferase (BGluT) isolated previously from Synechococcus sp. PCC 7942. The knockout mutant was unable to produce cyanopterin but only 6-hydroxymethylpterin-beta-galactoside, verifying that slr1166 encodes a pteridine glycosyltransferase, which is responsible for transfer of the second sugar glucuronic acid in cyanopterin synthesis. The mutant was affected in its intracellular pteridine content and growth rate, which were 74% and 80%, respectively, of wild type, demonstrating that the second sugar residue is still required for quantitative maintenance of cyanopterin. This supports the previous suggestion that glycosylation may contribute to high cellular concentration of pteridine compounds.