Importance of the residue 190 on bactericidal activity of the bactericidal/permeability-increasing protein 5

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• Bactericidal/permeability-increasing protein (BPI) exhibits potent antibacterial and endotoxin-neutralizing properties, making it clinically relevant.
• The specific amino acid residues critical for BPI's bactericidal function have not been fully elucidated.
• A prior study linked a mutation in mouse BPI5 (mBPI5) to male infertility.

Purpose of the Study:

• To investigate the impact of the Asp190Ala mutation on the antibacterial activity of mBPI5.
• To elucidate the structural and functional basis for the contribution of residue 190 to mBPI5's activity.

Main Methods:

• Site-directed mutagenesis to create the Asp190Ala mutant of mBPI5.
• Assessment of cytotoxic effects against Escherichia coli J5 and Pseudomonas aeruginosa.
• Liposome co-sedimentation assays to quantify binding affinity to lipid components.
• Structural analysis of mBPI5 to understand residue interactions.

Main Results:

• The Asp190Ala mutation significantly enhanced the cytotoxic activity of mBPI5 against both Gram-negative bacteria tested.
• Liposome binding affinity increased approximately eightfold for the Asp190Ala mutant compared to wild-type mBPI5.
• Structural analysis revealed that mutating Asp190 disrupts salt linkages, freeing adjacent residues (e.g., Arg188) for enhanced interaction with lipopolysaccharides (LPS).

Conclusions:

• Residue 190, in conjunction with surrounding positively charged residues, plays a crucial role in the bactericidal and endotoxin-neutralizing capabilities of mBPI5.
• The enhanced antibacterial activity is attributed to improved binding affinity to the lipid A component of LPS.
• Understanding these residue-function relationships can guide the development of novel antimicrobial agents.