Histidine-rich glycoprotein exerts antibacterial activity

Histidine-rich glycoprotein (HRGP), an abundant heparin-binding protein found in plasma and thrombocytes, exerts antibacterial effects against Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). Fluorescence studies and electron microscopy to assess membrane permeation showed that HRGP induces lysis of E. faecalisbacteria in the presence of Zn2+ or at low pH. Heparin blocked binding of the protein to E. faecalis and abolished antibacterial activity. Furthermore, truncated HRGP, devoid of the heparin-binding and histidine-rich domain, was not antibacterial. It has previously been shown that peptides containing consensus heparin-binding sequences (Cardin and Weintraub motifs) are antibacterial. Thus, the peptide (GHHPH)4, derived from the histidine-rich region of HRGP and containing such a heparin-binding motif, was antibacterial for E. faecalis in the presence of Zn2+ or at low pH. The results show a previously undisclosed antibacterial activity of HRGP and suggest that the histidine-rich and heparin-binding domain of HRGP mediates the antibacterial activity of the protein.