Ligand-induced conformational changes in the capping subdomain of a bacterial old yellow enzyme homologue and conserved sequence fingerprints provide new insights into substrate binding.
We have recently reported that Shewanella oneidensis, a Gram-negative gamma-proteobacterium with a rich arsenal of redox proteins, possesses four old yellow enzyme (OYE) homologues. Here, we report a series of high resolution crystal structures for one of these OYEs, Shewanella yellow enzyme 1 (SYE1), in its oxidized form at 1.4A resolution, which binds a molecule of PEG 400 in the active site, and in its NADH-reduced and p-hydroxybenzaldehyde- and p-hydroxyacetophenone-bound forms at 1.7A resolution. Although the overall structure of SYE1 reveals a monomeric enzyme based on the alpha(8)beta(8) barrel scaffold observed for other OYEs, the active site exhibits a unique combination of features: a strongly butterfly-bent FMN cofactor both in the oxidized and NADH-reduced forms, a collapsed and narrow active site tunnel, and a novel combination of conserved residues involved in the binding of phenolic ligands. Furthermore, we identify a second p-hydroxybenzaldehyde-binding site in a hydrophobic cleft next to the entry of the active site tunnel in the capping subdomain, formed by a restructuring of Loop 3 to an "open" conformation. This constitutes the first evidence to date for the entire family of OYEs that Loop 3 may indeed play a dynamic role in ligand binding and thus provides insights into the elusive NADH complex and into substrate binding in general. Structure-based sequence alignments indicate that the novelties we observe in SYE1 are supported by conserved residues in a number of structurally uncharacterized OYEs from the beta- and gamma-proteobacteria, suggesting that SYE1 represents a new subfamily of bacterial OYEs.
van den Hemel
Debbie
D
Department of Biochemistry, Physiology and Microbiology, Laboratory for Protein Biochemistry and Protein Engineering, K.L. Ledeganckstraat 35, Ghent University, 9000 Ghent, Belgium.
Brigé
Ann
A
Savvides
Savvas N
SN
Van Beeumen
Jozef
J
D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D008024:Ligands; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009252:NADPH Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D020592:Shewanella / Q000201:enzymology*
D008024:Ligands; D009243:NAD; D009252:NADPH Dehydrogenase