UDP‐glucose dehydrogenase from bovine liver: Primary structure and relationship to other dehydrogenases

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Abstract
The primary structure of bovine liver UDP‐glucose dehydrogenase (UDPGDH), a hexameric, NAD+‐linked enzyme, has been determined at the protein level. The 52‐kDa subunits are composed of 468 amino acid residues, with a free N‐terminus and a Ser/Asn microheterogeneity at one position. The sequence shares 29.6% positional identity with GDP‐mannose dehydrogenase from Pseudomonas, confirming a similarity earlier noted between active site peptides. This degree of similarity is comparable to the 31.1% identity vs. the UDPGDH from type A Streptococcus. Database searching also revealed similarities to a hypothetical sequence from Salmonella typhimurium and to “UDP‐N‐acetyl‐mannosaminuronic acid dehydrogenase” from Escherichia coli. Pairwise identities between bovine UDPGDH and each of these sequences were all in the range of ∼26–34%. Multiple alignment of all 5 sequences indicates common ancestry for these 4‐electron‐transferring enzymes. There are 27 strictly conserved residues, including a cysteine residue at position 275, earlier identified by chemical modification as the expected catalytic residue of the second half‐reaction (conversion of UDP‐aldehydoglucose to UDP‐glucuronic acid), and 2 lysine residues, at positions 219 and 338, one of which may be the expected catalytic residue for the first half‐reaction (conversion of UDP‐glucose to UDP‐aldehydoglucose). A GXGXXG pattern characteristic of the coenzyme‐binding fold is found at positions 11–16, close to the N‐terminus as with “short‐chain” alcohol dehydrogenases. Because the enzyme combines functionalities of alcohol and aldehyde dehydrogenases, it was also of interest to search specifically for other sequence similarities to either of these 2 enzymes, as well as to histidinol dehydrogenase, another 4‐electron‐transferring dehydrogenase, but none were found.