UDP-GLUCOSE DEHYDROGENASE FROM BOVINE LIVER - PRIMARY STRUCTURE AND RELATIONSHIP TO OTHER DEHYDROGENASES

The primary structure of bovine liver UDP-glucose dehydrogenase (UDPGD H), a hexameric, NAD(+)-linked enzyme, has been determined at the prot ein level. The 52-kDa subunits are composed of 468 amino acid residues , with a free N-terminus and a Ser/Asn microheterogeneity at one posit ion. The sequence shares 29.6% positional identity with GDP-mannose de hydrogenase from Pseudomonas, confirming a similarity earlier noted be tween 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 deh ydrogenase'' from Escherichia coli. Pairwise identities between bovine UDPGDH and each of these sequences were all in the range of similar t o 26-34%. Multiple alignment of all 5 sequences indicates common ances try for these 4-electron-transferring enzymes. There are 27 strictly c onserved residues, including a cysteine residue at position 275, earli er identified by chemical modification as the expected catalytic resid ue of the second half-reaction (conversion of UDP-aldehydoglucose to U DP-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 positi ons 11-16, close to the N-terminus as with ''short-chain'' alcohol deh ydrogenases. Because the enzyme combines functionalities of alcohol an d aldehyde dehydrogenases, it was also of interest to search specifica lly for other sequence similarities to either of these 2 enzymes, as w ell as to histidinol dehydrogenase, another 4-electron-transferring de hydrogenase, but none were found.