Crystal structures and kinetics ofN-acetylneuraminate lyase fromFusobacterium nucleatum

Abstract

N-Acetyl-D-neuraminic acid lyase (NanA) catalyzes the breakdown of sialic acid (Neu5Ac) toN-acetyl-D-mannosamine (ManNAc) and pyruvate. NanA plays a key role in Neu5Ac catabolism in many pathogenic and bacterial commensals where sialic acid is available as a carbon and nitrogen source. Several pathogens or commensals decorate their surfaces with sialic acids as a strategy to escape host innate immunity. Catabolism of sialic acid is key to a range of host–pathogen interactions. In this study, atomic resolution structures of NanA fromFusobacterium nucleatum(FnNanA) in ligand-free and ligand-bound forms are reported at 2.32 and 1.76 Å resolution, respectively. F. nucleatumis a Gram-negative pathogen that causes gingival and periodontal diseases in human hosts. Like other bacterialN-acetylneuraminate lyases, FnNanA also shares the triosephosphate isomerase (TIM)-barrel fold. As observed in other homologous enzymes, FnNanA forms a tetramer. In order to characterize the structure–function relationship, the steady-state kinetic parameters of the enzyme are also reported.