This is the C-terminal domain found in proteins in a range of Proteobacteria as well as the Gram-positive Oceanobacillus iheyensis. Structural analysis of the whole protein indicates the N- and C-termini act together to produce a surface into which a threonate-ADP complex is bound, demonstrating that a sugar binding site is on the N-terminal domain, and a nucleotide binding site is in the C-terminal domain [1]. There is a critical motif, DDXTG, at approximately residues 22-25. Proteins containing this domain have been predicted as kinases. Some members are associated with PdxA2 by physical clustering and gene fusion with PdxA2. Some members that are fused with PdxA2 have been shown to be involved in L-4-hydroxythreonine (4HT) phosphorylation, part of the alternative pathway to make PLP (pyridoxal 5'-phosphate) out of a toxic metabolite, 4HT. However, 4HT phosphorylation might not be the main function of this group of proteins. Moreover, some members that are not associated with pdxA2, and even one that is associated with pdxA2, have lost 4HT kinase activity [2]. Functional analysis demonstrate that family members include D-Threonate kinases (DtnK), D-Erythronate kinases (DenK) and 3-Oxo-tetronate kinases (OtnK) [1].

1: Assignment of function to a domain of unknown function: DUF1537 is a new kinase family in catabolic pathways for acid sugars. Zhang X, Carter MS, Vetting MW, San Francisco B, Zhao S, Al-Obaidi NF, Solbiati JO, Thiaville JJ, de Crecy-Lagard V, Jacobson MP, Almo SC, Gerlt JA; Proc Natl Acad Sci U S A. 2016;113:E4161-E4169. PMID:27402745

2: Members of a Novel Kinase Family (DUF1537) Can Recycle Toxic Intermediates into an Essential Metabolite. Thiaville JJ, Flood J, Yurgel S, Prunetti L, Elbadawi-Sidhu M, Hutinet G, Forouhar F, Zhang X, Ganesan V, Reddy P, Fiehn O, Gerlt JA, Hunt JF, Copley SD, de Crecy-Lagard V; ACS Chem Biol. 2016;11:2304-2311. PMID:27294475