Fibronectin binding protein A
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. This is true over a range of different cell types. 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
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)
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 
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. 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.
The FnBP is involved in adherence to a wide range of mammalian cells and is hence implicated in various infections.
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
FnBPs are essential in the formation of biofilms by community-associated methicillin-resistant Staphylococcus aureus strain LAC. They are specifically involved in primary attachment.
- Jönsson K, Signäs C, Müller HP, Lindberg M (December 1991). "Two different genes encode fibronectin binding proteins in Staphylococcus aureus. The complete nucleotide sequence and characterization of the second gene". European journal of biochemistry / FEBS 202 (3): 1041–8. doi:10.1111/j.1432-1033.1991.tb16468.x. PMID 1837266.
- Sinha B, Francois P, Que YA, Hussain M, Heilmann C, Moreillon P, Lew D, Krause KH, Peters G, Herrmann M (2000). "Heterologously Expressed Staphylococcus aureus Fibronectin-Binding Proteins Are Sufficient for Invasion of Host Cells". Infect Immun. 68 (12): 6871–8. doi:10.1128/iai.68.12.6871-6878.2000. PMC 97792. PMID 11083807.
- Jett BD, Gilmore MS. (2002). "Internalization of Staphylococcus aureus by Human Corneal Epithelial Cells: Role of Bacterial Fibronectin-Binding Protein and Host Cell Factors". Infect Immun. 70 (8): 4697–700. doi:10.1128/iai.70.8.4697-4700.2002. PMC 128182. PMID 12117986.
- Ahmed S, Meghji S, Williams RJ, Henderson B, Brock JH, Nair SP. (2001). "Staphylococcus aureus Fibronectin Binding Proteins Are Essential for Internalization by Osteoblasts but Do Not Account for Differences in Intracellular Levels of Bacteria". Infect Immun. 69 (5): 2872–7. doi:10.1128/IAI.69.5.2872-2877.2001. PMC 98237. PMID 11292701.
- 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. PMID 12055657.
- Huveneers S, Truong H, Fässler R, Sonnenberg A, Danen EH. (2008). "Binding of soluble fibronectin to integrin alpha5 beta1 - link to focal adhesion redistribution and contractile shape". J Cell Sci. 121 (Pt 15): 2452–62. doi:10.1242/jcs.033001. PMID 18611961.
- 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:10.1097/01.qco.0000073771.11390.75. PMID 12821812.
- McCourt, Jennifer; O'Halloran, Dara P.; McCarthy, Hannah; O'Gara, James P.; Geoghegan, Joan A. (April 2014). "Fibronectin-binding proteins are required for biofilm formation by community-associated methicillin-resistant Staphylococcus aureus strain LAC". FEMS Microbiology Letters 353 (2): 157–164. doi:10.1111/1574-6968.12424.