Circular-dichroism studies on two β-lactamases from Bacillus cereus

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Abstract
The circular-dichroism (CD) spectra of β-lactamases I and II from Bacillus cereus 569/H are reported, along with that of the β-lactamase II free from carbohydrate. The results show that carbohydrate makes an appreciable contribution to the optical activity of β-lactamase II in the far-ultraviolet, and that removal of carbohydrate greatly affects the optical activity of several aromatic side chains of the protein moiety. Both tyrosyl and tryptophanyl residues are affected, showing that some of these residues must be near to the surface of the protein moiety, close to the site of attachment of the carbohydrate. Although the far-ultraviolet CD spectrum of β-lactamase II resembles that of a protein containing some β-structure, it can be shown that this is a consequence of the optical activity of carbohydrate in this region of the spectrum, and that the protein is likely to contain α-helix rather than β-pleated sheet structure. The overall structures of the protein components of β-lactamases I and II are similar, but not identical, as shown by the dissimilarity of the CD spectra when calculated on a mean residue basis.

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