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 specialized 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 characterized in Escherichia coli, is found in the γ subdivision of the proteobacteria. A second pathway of vitamin B6 synthesis involving the pdxS/SNZ and pdxT/SNO (see <PDOC00950>) protein families, which are completely unrelated in sequence to the pdxA/pdxJ proteins, is found in plants, fungi, protists, archaebacteria, and most bacteria.

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 [1]. 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 [2].

Proteins belonging to the pdxS/SNZ family occur in organisms in four kingdoms and form one of the most highly conserved family [3]. PdxS/SNZ proteins have a classic (β/α)8-barrel fold, consisting of eight parallel β-strands alternating with eight α helices (see <PDB:1ZNN>) [4].

Some proteins belonging to the pdxS/SNZ family are listed below:

• Bacillus subtilis pyridoxine biosynthesis protein pdxS.
• Haemophilus influenzae pyridoxine biosynthesis protein pdxS.
• Mycobacterium leprae pyridoxine biosynthesis protein pdxS.
• Mycobacterium tuberculosis pyridoxine biosynthesis protein pdxS.
• Archaeoglobus fulgidus pyridoxine biosynthesis protein pdxS.
• Methanococcus jannaschii pyridoxine biosynthesis protein pdxS.
• Methanococcus vannielii pyridoxine biosynthesis protein pdxS.
• Methanobacterium thermoautotrophicum pyridoxine biosynthesis protein pdxS.
• Cercospora nicotianae pyridoxine biosynthesis protein PDX1 or singlet oxygen resistance protein 1 (SOR1).
• Yeast pyridoxin biosynthesis protein SNZ1 (PDX1 homolog 1).
• Yeast probable pyridoxin biosynthesis protein SNZ2 (PDX1 homolog 2).
• Yeast probable pyridoxin biosynthesis protein SNZ3 (PDX1 homolog 3).
• Fission yeast probable pyridoxin biosynthesis PDX1-like protein.
• Hevea brasiliensis probable pyridoxin biosynthesis protein ER1 (PDX1 homolog) (ethylene-inducible protein HEVER).
• Stellaria longipes probable pyridoxin biosynthesis H47 (PDX1 homolog).

These are hydrophilic proteins of about 32 Kd. They can be picked up in the database by the following pattern. We also developed a profile for the pdxS/ SNZ family.