InterPro domain: IPR033755

The family of pyridoxal 5'-phosphate synthase subunits, known as the PdxS/SNZ family, occur in organisms in four kingdoms and form one of the most highly conserved families [ 1 ]. A PdxS/SNZ protein has a classic (beta/alpha)8-barrel fold, consisting of eight parallel beta-strands alternating with eight alpha helices. PdxS subunits form two hexameric rings [ 2 ]. Proteins are involved in vitamin B6 biosynthesis.

The term vitamin B6 is used to refer collectively to the compound pyridoxine and its vitameric forms, pyridoxal, pyridoxamine, and their phosphorylated derivatives. Vitamin B6 is required by all organisms and plays an essential role as a co-factor for enzymatic reactions. Plants, fungi, bacteria, archaebacteria, and protists synthetize vitamin B6. Animals and some highly specialised obligate pathogens obtain it nutritionally. Vitamin B6 has two distinct biosynthetic pathways, which do not coexist in any organism. The pdxA/pdxJ pathway, that has been extensively characterised in Escherichia coli, is found in the gamma subdivision of the proteobacteria. A second pathway of vitamin B6 synthesis involving the pdxS/SNZ and pdxT/SNO protein families, which are completely unrelated in sequence to the pdxA/pdxJ proteins, is found in plants, fungi, protists, archaebacteria and most bacteria [ 3 , 4 , 5 ].

PdxS/SNZ and pdxT/SNO proteins form a complex which serves as a glutamine amidotransferase to supply ammonia as a source of the ring nitrogen of vitamin B6 [ 6 ]. PdxT/SNO and pdxS/SNZ appear to encode respectively the glutaminase subunit, which produces ammonia from glutamine, and the synthase subunit, which combines ammonia with five- and three-carbon phosphosugars to form vitamin B6 [ 7 ].

This entry represents the N-terminal domain of the pyridoxal 5'-phosphate synthase subunit PdxS/SNZ.

1. A highly conserved sequence is a novel gene involved in de novo vitamin B6 biosynthesis. Proc. Natl. Acad. Sci. U.S.A. 96, 9374-8
2. A new arrangement of (beta/alpha)8 barrels in the synthase subunit of PLP synthase. J. Biol. Chem. 280, 27914-23
3. Structure of a bacterial pyridoxal 5'-phosphate synthase complex. Proc. Natl. Acad. Sci. U.S.A. 103, 19284-9
4. Structural insights into the mechanism of the PLP synthase holoenzyme from Thermotoga maritima. Biochemistry 45, 14609-20
5. On the two components of pyridoxal 5'-phosphate synthase from Bacillus subtilis. J. Biol. Chem. 280, 32291-300
6. Characterization of the products of the genes SNO1 and SNZ1 involved in pyridoxine synthesis in Saccharomyces cerevisiae. Eur. J. Biochem. 271, 745-52
7. Physical and enzymological interaction of Bacillus subtilis proteins required for de novo pyridoxal 5'-phosphate biosynthesis. J. Bacteriol. 186, 1191-6