Identification and characterization of a novel 38.5-kilodalton cell surface protein of Staphylococcus aureus with extended-spectrum binding activity for extracellular matrix and plasma proteins

The ability to attach to host ligands is a well-established pathogenic fact or in invasive Staphylococcus aureus disease. In addition to the family of adhesive proteins bound to the cell wall via the sortase A (srtA) mechanism , secreted proteins such as the fibrinogen-binding protein Efb, the extrace llular adhesion protein Eap, or coagulase have been found to interact with various extracellular host molecules. Here we describe a novel protein, the extracellular matrix protein-binding protein (Emp) initially identified in Western ligand blots as a 40-kDa protein due to its broad-spectrum recogni tion of fibronectin, fibrinogen, collagen, and vitronectin. Emp is expresse d in the stationary growth phase and is closely associated with the cell su rface and yet is extractable by sodium dodecyl sulfate. The conferring gene emp (1,023 nucleotides) encodes a signal peptide of 26 amino acids and a m ature protein of a calculated molecular mass of 35.5 kDa. Using PCR, emp wa s demonstrated in all 240 S. aureus isolates of a defined clinical strain c ollection as well as in 6 S. aureus laboratory strains, whereas it is lacki ng in all 10 S. epidermidis strains tested. Construction of an allelic repl acement mutant (mEmp50) revealed the absence of Emp in mEmp50, a significan tly decreased adhesion of mEmp50 to immobilized fibronectin and fibrinogen, and restoration of these characteristics upon complementation of mEmp50. E mp expression was also demonstrable upon heterologous complementation of S. carnosus. rEmp expressed in Escherichia coli interacted with fibronectin, fibrinogen, and vitronectin in surface plasmon resonance experiments at a K -d of 21 nM, 91 nM, and 122 pM, respectively. In conclusion, the biologic c haracterization of Emp suggests that it is a member of the group of secrete d S. aureus molecules that interact with an extended spectrum of host ligan ds and thereby contribute to S. aureus pathogenicity.