L-arginine:inosamine-phosphate amidinotransferase StrB1 from Streptomyces griseus (StrB1) and similar proteins
This subfamily includes inosamine-phosphate amidinotransferase (EC 2.1.4.2; also called inosamine amidinotransferase or inosamine-P amidinotransferase or scyllo-inosamine-4-phosphate amidinotransferase or L-arginine:inosamine phosphate amidinotransferase) from Streptomyces griseus (StrB1), among others. Inosamine-phosphate amidinotransferase catalyzes two non-consecutive transamidination reactions; it converts scyllo-inosamine 4-phosphate into N-amidino-scyllo-inosamine 4-phosphate, and N1-amidinostreptamine 6-phosphate into streptidine 6-phosphate. L-arginine:inosamine-phosphate amidinotransferase StrB1 is structurally similar to the human L-arginine:glycine amidinotransferase (AT), with residues involved in substrate binding and catalysis conserved in AT and StrB1 at equivalent topological positions, suggesting a similar reaction mechanism among amidinotransferases. This subfamily also includes putative inosamine-phosphate amidinotransferase 2 (StrB2), also called aminocyclitol amidinotransferase or inosamine-phosphate amidinotransferase II, from Streptomyces glaucescens. It is unclear if StrB2 participates in streptomycin biosynthesis as it contains an arginine residue instead of the nucleophilic cysteine that is a key residue for amidine transfer.
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