Structural Insight into the Substrate Gating Mechanism by Staphylococcus aureus Aldehyde Dehydrogenase

Abstract

Staphylococcus aureus produces staphyloxanthin, a C30 carotenoid with golden color, as an antioxidant to promote bacterial resistance to reactive oxygen spe- cies. The biosynthesis pathway of staphyloxanthin involves a series of catalytic enzymes. Aldehyde de-hydrogenase (AldH) is a dehydrogenase recently identified to convert 4,4’-diaponeurosporen-aldehyde into 4,4’-diaponeurosporenoic acid during staphyloxanthin biosynthesis. Here, we present the crystallographic structures of apo- and holo-forms of S. aureus AldH. The dimeric enzyme contains a unique C-terminal helix, which resembles a “gate-keeper” helix found in human membrane-bound fatty aldehyde dehydrogenase (FALDH). Particularly, the helix adopts “open” and “closed” conformations in apo- and holo-AldH, respectively, to control the access of the substrate tunnel. Mutagenesis in combination with in vitro and in vivo activity assays identifies several residues essential for S. aureus AldH substrate recognition and enzyme catalytic turnover. Our results provide insights into substrate recognition of S. aureus AldH toward polyunsaturat- ed long-chain aldehydes at atomic resolution.