Crystal structure of glutathione-independent formaldehyde dehydrogenase.

Formaldehyde dehydrogenase from Pseudomonas putida (PFDH) is a member of the zinc-containing medium-chain alcohol dehydrogenase (ADH) family. The pyridine nucleotide NAD(H) in PFDH, which is distinct from the coenzyme (as co-substrate) in typical ADHs, is tightly but not covalently bound to the protein and acts as a cofactor. Such enzymes with tightly bound NAD(P)(H) acting as a cofactor are called nicotinoproteins. The structural basis of the tightly bound cofactor of PFDH is unknown. The crystal structure of PFDH has been solved by the multiwavelength anomalous diffraction method using intrinsic zinc ions and has been refined at a 1.65 A resolution. The 170-kDa-homotetrameric PFDH molecule shows 222-point group symmetry. Although the secondary structure arrangement and the binding mode of catalytic and structural zinc ions in PFDH are similar to those of typical ADHs, a number of loop structures that differ between PFDH and ADHs in their lengths and conformations are observed.