A novel adhesin from Pasteurella multocida that binds to the integrin-binding fibronectin FnIII₉₁₀ repeats

Division of Microbial Diseases, UCL Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD; Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT; Dept of Pathology & Infectious Diseases, Royal Veterinary College, Hawkshead Lane, North Mimms, Herts AL9 7TA; School of Crystallography, Birkbeck College, University of London, Malet St. London WC1E 7HX

^* To whom correspondence should be addressed. Email: l.mullen{at}eastman.ucl.ac.uk.

	Abstract

Phage display screening with fragmented genomic DNA from the animal pathogen Pasteurella multocida has identified a gene encoding a putative fibronectin binding protein (19). Homologues of this gene (pm1665) are found in all other sequenced members of the Pasteurellaceae. Gene pm1665 has been cloned and the protein expressed. Recombinant PM1665 binds to both soluble and immobilised fibronectin and is unique in that it interacts with the integrin-binding fibronectin type III repeats FnIII_9-10 and not, as is the case for almost all other fibronectin adhesins, to the N-terminal type I repeats. Surface plasmon resonance analysis reveals a complex binding mechanism with a K_D of 150 nM ± 70 nM. Bioinformatic analysis suggests that PM1665 contains two helix-hairpin-helix (HhH) motifs and truncation mutation studies have identified the binding site in this protein as a combination of these two HhH motifs in conjunction with a conserved amino acid motif – VNINTA. We have shown that PM1665 is on the cell surface and binding of P. multocida to fibronectin is almost completely inhibited by anti-PM1665 antiserum. These results support the hypothesis that PM1665 is a member of a new family of fibronectin binding adhesins that are important in the adhesion of P. multocida to fibronectin.