Conformational changes in the fibronectin binding MSCRAMMs are induced by ligand binding.
Bacterial adherence to host tissue involves specific microbial surface adhesins of which a subfamily termed microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) specifically recognize extracellular matrix components. We now report on the biophysical characterization of recombinant fibronectin binding MSCRAMMs originating from several different species of Gram-positive bacteria. The far-UV CD spectra (190-250 nm) of recombinant forms of the ligand binding domain of the MSCRAMMs, in a phosphate-buffered saline solution at neutral pH, were characteristic of a protein containing little or no regular secondary structure. The intrinsic viscosity of this domain was found to be the same in the presence or absence of 6 M guanidine hydrochloride, indicating that the native and denatured conformations are indistinguishable. On addition of fibronectin NH2 terminus as ligand to the recombinant adhesin there is a large change in the resulting far-UV CD difference spectra. At a 4.9 M excess of the NH2 terminus the difference spectra shifted to what was predominately a beta-sheet conformation, as judged by comparison with model far-UV CD spectra. The fibronectin NH2-terminal domain undergoes a minute but reproducible blue-shift of its intrinsic tryptophan fluorescence on addition of rFNBD-A, which contains no tryptophan residues. Since this result indicates that there is no large change in the environment of the tryptophan residues of the NH2 terminus on binding, the large shift in secondary structure observed by CD analysis is attributed to induction of a predominately beta-sheet secondary structure in the adhesin on binding to fibronectin NH2 terminus.
House-Pompeo
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Center for Extracellular Matrix Biology, Texas A & M University, Houston 77030, USA.
Xu
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Joh
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Speziale
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Höök
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D018829:Adhesins, Bacterial / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002942:Circular Dichroism; D005353:Fibronectins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D019791:Guanidine; D006146:Guanidines; D008024:Ligands; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013211:Staphylococcus aureus; D013291:Streptococcus; D013297:Streptococcus pyogenes; D014364:Tryptophan / Q000032:analysis
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D005353:Fibronectins; D006146:Guanidines; D008024:Ligands; D010446:Peptide Fragments; D011994:Recombinant Proteins; C048165:adhesin, Staphylococcus aureus; D014364:Tryptophan; D019791:Guanidine