Two different genes encode fibronectin binding proteins in Staphylococcus aureus

The complete nucleotide sequence and characterization of the second gene

Authors


  • Note. The novel nucleotide sequence data published here has been submitted to the EMBL sequence data bank and is available under accession number X62992.

Correspondence to C. Signäs, Department of Microbiology, Box 7025, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden

Abstract

A gene encoding a fibronectin binding protein (FnBP) has recently been isolated and sequenced from Staphylococcus aureus strain 8325–4. In the same bacterial strain, 682 bp downstream to the stop codon of this gene (fnbA), a second gene termed fnbB has now been discovered, encoding another FnBP (FnBPB). The two genes show in large parts striking sequence homologies. The complete amino acid sequence encoded by fnbB has been deduced and compared to that deduced from fnbA. In FnBPB a stretch of 66 amino acids downstream to the signal peptide has 75% identity with the corresponding region in FnBPA. At the C-terminal site another 394 amino acid stretch is almost identical in both gene products. This stretch contains the 38 amino acid long D repeats, the wall spanning Wr repeats and the hydrophobic membrane spanning domain. In FnBPA each of the three D repeats has been identified as a fibronectin binding structure. These structures are highly conserved in FnBPB and most likely represent the major Fn-binding domain of this protein. However, a subclone of gene fnbB lacking the coding region for the D repeats also clearly expresses fibronectin binding activity. This additional binding site is so far unique for FnBPB and interacts like the D domains with the N-terminal 24–31-kDa fragment of fibronectin. The purified recombinant FnBP fragment (not containing the D repeats) completely inhibits the binding of fibronectin to whole cells of S. aureus.

Abbreviations
Fn

fibronectin

FnBP

Fn binding protein

FnBPA

FnBP encoded by fnbA

FnBPB

FnBP encoded by fnbB

Enzymes
 

Thermolysin (EC 3.4.24.4)

 

lysozyme (EC 3.2.1.17)

Ancillary

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