This family is thiamine-phosphate synthase, and it belongs to the SCOP phosphomethylpyrimidine kinase C-terminal domain-like family. Vitamin B1 (thiamine pyrophosphate) is involved in several microbial metabolic functions. Thiamine biosynthesis is accomplished by joining two intermediate molecules that are synthesized separately, HMP-PP and HET-P. In the archaeon Natrialba magadii, ThiE and ThiN, are known to join HMP-PP ( hydroxymethylpyrimidine pyrophosphate) and HET-P (hydroxyethylthiazole phosphate) to generate thiamine phosphate. Whereas ThiE in Natrialba magadii is a mono-functional protein, ThiN exists as a C-terminal domain in a ThiDN fusion protein - examples of all three forms, from various prokaryotes, are found in this family [1,2].

1: Systematic discovery of analogous enzymes in thiamin biosynthesis. Morett E, Korbel JO, Rajan E, Saab-Rincon G, Olvera L, Olvera M, Schmidt S, Snel B, Bork P; Nat Biotechnol. 2003;21:790-795. PMID:12794638

2: A comparative genomics perspective on the genetic content of the alkaliphilic haloarchaeon Natrialba magadii ATCC 43099T. Siddaramappa S, Challacombe JF, Decastro RE, Pfeiffer F, Sastre DE, Gimenez MI, Paggi RA, Detter JC, Davenport KW, Goodwin LA, Kyrpides N, Tapia R, Pitluck S, Lucas S, Woyke T, Maupin-Furlow JA; BMC Genomics. 2012;13:165. PMID:22559199