The structure of a novel membrane‐associated 6‐phosphogluconate dehydrogenase from<i>Gluconacetobacter diazotrophicus</i>(<i>Gd</i>6PGD) reveals a subfamily of short‐chain 6PGDs
Pedro D. Sarmiento‐Pavía, Annia Rodríguez‐Hernández, Adela Rodríguez‐Romero, Martha E. Sosa‐Torres
Abstract
The enzyme 6‐phosphogluconate dehydrogenase catalyzes the conversion of 6‐phosphogluconate to ribulose‐5‐phosphate. It represents an important reaction in the oxidative pentose phosphate pathway, producing a ribose precursor essential for nucleotide and nucleic acid synthesis. We succeeded, for the first time, to determine the three‐dimensional structure of this enzyme from an acetic acid bacterium, Gluconacetobacter diazotrophicus ( Gd 6PGD). Active Gd 6PGD, a homodimer (70 kDa), was present in both the soluble and the membrane fractions of the nitrogen‐fixing microorganism. The Gd 6PGD belongs to the newly described subfamily of short‐chain (333 AA) 6PGDs, compared to the long‐chain subfamily (480 AA; e.g., Ovis aries, Homo sapiens ). The shorter amino acid sequence in Gd 6PGD induces the exposition of hydrophobic residues in the C‐terminal domain. This distinct structural feature is key for the protein to associate with the membrane. Furthermore, in terms of function, the short‐chain 6PGD seems to prefer NAD + over NADP + , delivering NADH to the membrane‐bound NADH dehydrogenase of the microorganisms required by the terminal oxidases to reduce dioxygen to water for energy conservation. Enzyme ECnonbreakingspace1.1.1.343 . Database Structural data are available in PDB database under the accession number 6VPB .