Protein-A-mediated targeting of bacteriochlorophyll-IgG to Staphylococcus aureus: a model for enhanced site-specific photocytotoxicity.

Abstract

A model for studying the efficiency of photodynamic action with a photosensitizer placed exclusively on the bacterial cell wall has been used. Bacteriochlorophyllide molecules, conjugated to rabbit immunoglobulin G (IgG), were synthesized. The conjugated pigment bacteriochlorophyll (Bchl)-IgG bound with high specificity to protein-A residues naturally exposed on the cell wall of the bacterium Staphylococcus aureus Cowan I. In bacterial suspensions the phototoxicity of the targeted conjugates (0.5-2.5 pigment per IgG molecule) was dose dependent (LD50 = 1.7 microM) in the presence of light (lambda > 550 nm) and inhibited by native IgG but not by ovalbumin, suggesting selective interaction with protein-A on the bacterial cell wall. No dark toxicity was noticed even with the highest conjugate concentration tested. In contrast, the photocytotoxicity of bacteriochlorophyll-serine (Bchl-Ser, LD50 = 0.07 microM) used as a nontargeted control was not inhibited by IgG. In spite of its lower apparent potency, Bchl-IgG was found to be 30 times more efficacious than Bchl-Ser: At LD50, only 66,000 Bchl-IgG molecules were bound per bacterium compared to 1,900,000 molecules of Bchl-Ser. The higher efficacy of Bchl-IgG is explained by its exclusive position on the bacterial cell wall. Consequently, photogeneration of oxidative species is confined to the cell wall and its vicinity, a seemingly highly susceptible domain for photodynamic action. In considering the design of cell-specific sensitizers for bacterial and cancer therapies, it would be beneficial to identify the more discretely sensitive subcellular domains as targets.

• Authors: S Gross, A Brandis, L Chen, V Rosenbach-Belkin, S Roehrs, A Scherz, Y Salomon
• Journal: Photochemistry and photobiology (Photochem Photobiol) Vol. 66 Issue 6 Pg. 872-8 (Dec 1997) ISSN: 0031-8655 [Print] United States
• PMID: 9421974 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Bacteriochlorophylls
• Immunoglobulin G
• Photosensitizing Agents
• Staphylococcal Protein A

Topics

• Bacteriochlorophylls (metabolism)
• Binding Sites
• Cell Wall (metabolism)
• Immunoglobulin G (metabolism)
• Light
• Models, Biological
• Photosensitizing Agents (metabolism)
• Staphylococcal Protein A (metabolism)
• Staphylococcus aureus (metabolism, radiation effects)