This entry includes D-galactarate dehydratase (GarD, EC:4.2.1.42) which catalyses the reaction D-galactarate = 5-keto-4-deoxy-D glucarate + H2O, [1] and altronate hydrolase (altronic acid hydratase, EC:4.2.1.7), which catalyses D-altronate = 2-keto-2- deoxygluconate + H2O [2]. As purified, both enzymes are catalytically inactive in the absence of added Fe2+, Mn2+, and beta-mercaptoethanol. Synergistic activation of altronate hydrolase activity is seen in the presence of both iron and manganese ions, suggesting that the enzyme may have two ion binding sites. Mn2+ appears to be part of the enzyme active centre, but the function of the single bound Fe2+ ion is unknown. The hydratase has no Fe-S core [3]. GarD structure revealed that it is a dimer in solution; each monomer has three domains, an N-terminal SAF domain (Pfam:PF08666), a second domain represented in this entry and a C-terminal domain [5]. This domain consists of three parallel beta-strands, surrounded by three alpha-helices and it interacts with the C-terminal domain from the second chain to form a dimerisation surface [5].

1: Evolution of enzymatic activities in the enolase superfamily: characterization of the (D)-glucarate/galactarate catabolic pathway in Escherichia coli. Hubbard BK, Koch M, Palmer DR, Babbitt PC, Gerlt JA; Biochemistry 1998;37:14369-14375. PMID:9772162

2: A 35.7 kb DNA fragment from the Bacillus subtilis chromosome containing a putative 12.3 kb operon involved in hexuronate catabolism and a perfectly symmetrical hypothetical catabolite-responsive element. Rivolta C, Soldo B, Lazarevic V, Joris B, Mauel C, Karamata D; Microbiology 1998;144:877-884. PMID:9579062

3: The role of iron in the activation of mannonic and altronic acid hydratases, two Fe-requiring hydro-lyases. Dreyer JL; Eur J Biochem 1987;166:623-630. PMID:3038546

4: The emergence of catalytic and structural diversity within the beta-clip fold. Iyer LM, Aravind L; Proteins. 2004;55:977-991. PMID:15146494

5: Structure of galactarate dehydratase, a new fold in an enolase involved in bacterial fitness after antibiotic treatment. Rosas-Lemus M, Minasov G, Shuvalova L, Wawrzak Z, Kiryukhina O, Mih N, Jaroszewski L, Palsson B, Godzik A, Satchell KJF; Protein Sci. 2020;29:711-722. PMID:31811683