Escherichia coli and other enteric bacteria contain two closely related D-tagatose 1,6-bisphosphate (TagBP)-specific aldolases involved in catabolism of galactitol (genes gatY gatZ) and of N-acetyl-galactosamine and D-galactosamine (genes kbaY, kbaZ, also called agaY, agaZ). The catalytic subunits GatY/KbaY alone are sufficient to show aldolase activity and contain most or all of the residues that have been identified as essential in substrate/product recognition and catalysis for class II aldolases [1, 2]. However, these aldolases differ from other Class II aldolases (which are homodimeric enzymes) in that they require subunits GatZ/KbaZ for full activity and for good in vivo and in vitro stability. The Z subunits alone do not show any aldolase activity [1]. This entry represents GatZ and KbaZ subunits. This entry also includes the D-tagatose 6-phosphate 4-epimerase Atu3167 from Agrobacterium fabrum which catalyzes the epimerization of D-tagatose 6-phosphate to D-fructose 6-phosphate [3]. It should be noted that the previous suggestion of a tagatose 6P-kinase function for other members of this family has been debated [4, 1, 5].

1: Two class II D-tagatose-bisphosphate aldolases from enteric bacteria. Brinkkotter A, Shakeri-Garakani A, Lengeler JW; Arch Microbiol. 2002;177:410-419. PMID:11976750

2: Molecular analysis of the gat genes from Escherichia coli and of their roles in galactitol transport and metabolism. Nobelmann B, Lengeler JW; J Bacteriol. 1996;178:6790-6795. PMID:8955298

3: ATP-binding Cassette (ABC) Transport System Solute-binding Protein-guided Identification of Novel d-Altritol and Galactitol Catabolic Pathways in Agrobacterium tumefaciens C58. Wichelecki DJ, Vetting MW, Chou L, Al-Obaidi N, Bouvier JT, Almo SC, Gerlt JA; J Biol Chem. 2015;290:28963-28976. PMID:26472925

4: Pathways for the utilization of N-acetyl-galactosamine and galactosamine in Escherichia coli. Brinkkotter A, Kloss H, Alpert C, Lengeler JW; Mol Microbiol. 2000;37:125-135. PMID:10931310

5: Galactitol catabolism in Sinorhizobium meliloti is dependent on a chromosomally encoded sorbitol dehydrogenase and a pSymB-encoded operon necessary for tagatose catabolism. Kohlmeier MG, White CE, Fowler JE, Finan TM, Oresnik IJ; Mol Genet Genomics. 2019;294:739-755. PMID:30879203