It is an
adhesin which enables Staphylococcus aureus (S. aureus) to adhere to host cells of another organism, and an
invasin facilitating its internalisation into these cells.[2] This is true over a range of different cell types.[2][3][4] The FnBP alone is capable of providing this invasive property, without the requirement of co-receptors. Even FnBP coated beads have been shown to become internalised into cells[2]
S. aureus is able to bind to host cells in the absence of the FnBP, but its adherence and invasive properties are much reduced (up to a 500-fold decrease in number of internalised cells)[2]
Structure
The FnBP inserts into the cell wall of S. aureus by means of a C-terminal LPXTG anchor. Two fibronectin binding domains have been identified - one is present in the C-terminal D repeat region, and one in the N-terminal A region [5]
Mechanism
The fibronectin binding protein is able to bind fibronectin present in the extracellular matrix. Similarly, the
α5β1 integrin present on host cells also binds fibronectin to create a link to its
actin cytoskeleton, binding via the Arg-Gly-Asp (RGD) motif present in fibronectin.[6] Fibronectin is able to act as a ‘bridge’ between S. aureus and the host cell, with both S. aureus and the host cell binding at either end of the molecule, and therefore facilitate adherence.[2]
Clinical significance
The FnBP is involved in adherence to a wide range of mammalian cells and is hence implicated in various infections.[7]
It is implicated in the pathogenesis of
osteomyelitis, and is the predominant adhesin for adherence to
osteoblasts, a cell type present in large quantities within bone. Few S. aureus cells become internalised into osteoblasts in the absence of the FnBP[4]
FnBPs are essential in the formation of biofilms by community-associated methicillin-resistant Staphylococcus aureus strain LAC. They are specifically involved in primary attachment.[8]
^Williams RJ, Henderson B, Nair SP (2002). "Staphylococcus aureus fibronectin binding proteins A and B possess a second fibronectin binding region that may have biological relevance to bone tissues". Calcif Tissue Int. 70 (5): 416–21.
doi:
10.1007/s00223-001-2073-z.
PMID12055657.
^Menzies BE. (2003). "The role of fibronectin binding proteins in the pathogenesis of Staphylococcus aureus infections". Current Opinion in Infectious Diseases. 16 (3): 225–9.
doi:
10.1097/00001432-200306000-00007.
PMID12821812.