Biochemical and structural characterization of a Class A β-lactamase fromNocardia cyriacigeorgica

Nocardia are gram-positive bacteria from the Actinobacteria phylum. Some Nocardia species can infect humans and are usually considered opportunist pathogens as they often infect immunocompromised patients. Albeit, their clinical incidence is low, many Nocardia species are nowadays considered emerging pathogens. Primary sites of infection of Nocardia are the skin or the lungs but dissemination to other body parts is very frequent. These disseminated infections are very difficult to treat and thus, tackled with multiple classes of antibiotics, on top of the traditional treatment targeting the folate pathway. ß-lactams are often included in the regimen but many Nocardia species present moderate or strong resistance to some of this drug class. Genomic, microbiological, and biochemical studies have reported the presence of class A ß-lactamases (ABL) in a handful of Nocardia species but no structural investigation of Nocardia ß-lactamases has been performed yet. In this study, we report the expression, purification, and preliminary biochemical characterization of the ABL from a Nocardia cyriacigeorgica (NCY-1) clinical strain. We describe, as well, the crystallization and the very high-resolution crystal structure of NCY-1. The protein sequence and structural analysis demonstrate that NCY-1 belongs to ß-lactamase of class A1 and attest to its very high conservation with ABL from other human pathogenic Nocardia . In addition, the presence of one molecule of citrate tightly bound in the catalytic site of the enzyme is described. This structure may provide a solid basis for future drug development to specifically target Nocardia spp. ß-lactamases. Synopsis The crystal structure at high resolution of a class A ß-lactamase from a clinical strain of Nocardia cyriacigeorgica is reported.