Glucose-6-phosphate dehydrogenase. Structure-function relationships and the Pichia jadinii enzyme structure.

The primary structure of glucose-6-phosphate dehydrogenase from the yeast Pichia jadinii (formerly Candida utilis) has been determined. It consists of a 495-residue, N-terminally acetylated protein chain. The structure shows extensive differences from those of the corresponding mammalian, fruit fly, and bacterial enzymes (52-68% residue non-identities), but also from that of another yeast, Saccharomyces cerevisiae (38%). A eubacterial type and a yeast type of glucose-6-phosphate dehydrogenase are discerned, in addition to the known mammalian type. They are distinguished from each other, from the mammalian type, and the insect enzyme, on the basis of both specific residues and pattern differences. The distribution of residues conserved in all forms locates short segments in which identities are closely grouped. Approximately 50% of these segments correspond to predicted turns and appear to mark the principal folds characteristic of the enzyme's tertiary structure. A region in the N-terminal part of the protein chain has characteristics suggestive of a coenzyme-binding site, while, in the middle third, another functionally important segment may be related to glucose-6-phosphate binding and catalysis.