The Multifunctional Staphylococcus aureus Autolysin Aaa Mediates Adherence to Immobilized Fibrinogen and Fibronectin

Staphylococci can cause a wide spectrum of infections, including endocarditis, osteomyelitis, and sepsis, which is reflected by the numerous virulence factors they produce, among them a recently identified new class of adhesins, namely, the multifunctional autolysins/adhesins. Here we report the identification and molecular characterization of Aaa, a novel autolysin/adhesin from Staphylococcus aureus. The gene encoding Aaa was cloned from the clinical isolate Staphylococcus aureus 4074. DNA sequence analysis revealed that aaa encodes a deduced protein of 334 amino acids with a predicted molecular mass of 35.8 kDa. Aaa contains three N-terminal repetitive sequences that comprise features of a peptidoglycan-binding domain, the LysM domain. The expression of aaa by Escherichia coli and its subsequent characterization revealed that Aaa possesses bacteriolytic activity as well as adhesive properties, such as binding to extracellular matrix proteins. Real-time biomolecular interaction analysis demonstrated that the interaction of Aaa with fibrinogen, fibronectin, and vitronectin is dose dependent and saturable and occurs with a high affinity. Furthermore, we demonstrate that Aaa binds to the Aalpha and Bbeta chains of fragment D of fibrinogen. Immunofluorescence microscopy revealed that Aaa is located at the cell surface. Finally, an aaa knockout mutant showed reduced adherence to surface-adsorbed fibrinogen and fibronectin, strongly suggesting a role for Aaa in the colonization of host factor-coated polymer surfaces and/or host tissue.