Membrane-bound penicillinases in Gram-positive bacteria

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Penicillinases in Gram-positive bacteria (Bacillus, Staphylococcus) differ in localization from Gram-negative organisms, with Gram-positives having membrane-bound forms.
• Gram-negative penicillinases are typically periplasmic, while Gram-positive counterparts exhibit significant hydrophobic membrane association.

Purpose of the Study:

• To investigate the mechanism of membrane attachment for penicillinases in Staphylococcus aureus and Bacillus cereus.
• To determine if the glyceride thioether modification, previously identified in Bacillus licheniformis, is conserved in other Gram-positive bacteria.

Main Methods:

• Isotopic labeling using [3H]palmitate to detect lipid modification.
• Assessing the effect of the antibiotic globomycin, known to interfere with glyceride thioether processing.
• Isolation and identification of glyceryl cysteine sulfone, an oxidation product of the modified cysteine residue.

Main Results:

• Membrane penicillinases from S. aureus and B. cereus were confirmed to possess the glyceride thioether modification.
• The antibiotic globomycin affected these modified penicillinases, similar to its effect on Gram-negative outer membrane proteins.
• Structural features within signal sequences of Gram-positive and Gram-negative penicillinases were compared to identify determinants for modification and membrane anchoring.

Conclusions:

• The glyceride thioether modification is a conserved mechanism for membrane anchorage of penicillinases in both Gram-positive and Gram-negative bacteria.
• Specific structural elements in signal sequences dictate susceptibility to modification and subsequent cleavage, leading to membrane attachment.