Circular-dichroism studies on two -lactamases from Bacillus cereus

Area of Science:

• Biochemistry
• Protein Structure Analysis
• Spectroscopy

Background:

• Beta-lactamases are crucial enzymes in bacterial resistance.
• Understanding their structure is key to developing inhibitors.
• Bacillus cereus produces beta-lactamases I and II, with II being glycosylated.

Purpose of the Study:

• To analyze the circular-dichroism (CD) spectra of beta-lactamases I and II.
• To investigate the contribution of carbohydrate to beta-lactamase II's optical activity.
• To determine the secondary structure of the protein moiety accurately.

Main Methods:

• Circular-dichroism (CD) spectroscopy was employed.
• Comparison of CD spectra for native and deglycosylated beta-lactamase II.
• Analysis of far-ultraviolet CD spectra to infer secondary structure.

Main Results:

• Carbohydrate significantly contributes to beta-lactamase II's optical activity in the far-ultraviolet region.
• Removal of carbohydrate altered the optical activity of aromatic side chains (tyrosyl, tryptophanyl).
• The apparent beta-structure in beta-lactamase II's CD spectrum was attributed to carbohydrate; the protein moiety is predominantly alpha-helical.

Conclusions:

• The carbohydrate moiety of beta-lactamase II significantly influences its CD spectra, masking the true protein secondary structure.
• Beta-lactamase II's protein component is primarily alpha-helical, not beta-pleated sheet.
• The protein structures of beta-lactamases I and II are similar but not identical.