| Type: | Family | Name: | Thiazole biosynthetic enzyme Thi4 family |
| Description: | Thiamine (vitamin B1) can be synthesised de novo in prokaryotes, plants and fungi. In eukaryotes, THI4 is involved in the biosynthesis of the thiamine precursor thiazole, and is repressed by thiamine [].Archaea harbour structural homologues of both the bacterial (ThiS-ThiF) and eukaryotic (THI4) proteins for thiazole synthesis. Most archaea have homologues that cluster to the THI4 family of proteins, but lack the conserved cysteine residue of the yeast THI4p that is required for sulfur transfer in formation of the thiazole ring. Instead, they have a histidine residue that is well conserved. Initially, these archaeal histidine-cointaining THI4 homologues were reported to convert ribose-1,5-bisphosphate (R15P) into ribulose-1,5-bisphosphate, the substrate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) [], but this may not be correct and their function remains unknown []. On the other hand, archaeal THI4 homologues with a conserved catalytic cysteine are linked to thiamine biosynthesis [].This family is represented by THI4 and also includes chloroplastic thiamine thiazole synthase Thi1 [, ] and prokaryotic proteins. | Short Name: | Thi4_fam |
