Sequence analysis of surface proteins from Gram-positive bacteria indicates a composite organization consisting of unique and repeated segments. Thus, these proteins may contain discrete domains that could fold independently. In this paper, we have used a panel of biophysical methods, including gel permeation chromatography, analytical ultracentrifugation, circular dichroism, and fluorescence spectroscopy, to analyze the structural organization of the Staphylococcus aureus collagen adhesin, CNA. Our results indicate that the structure, function, and folding of the ligand-binding domain (A) are not affected by the presence or absence of the other major domain (B). In addition, little or no interaction is observed between the nearly identical repeat units within the B domain. We propose that CNA is indeed a mosaic protein in which the different domains previously indicated by sequence analysis operate independently.
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