NEW YORK (Reuters Health) Jun 25 – Investigators in Texas have determined the structure of the highly variable region of an outer lipoprotein of Borrelia burgdorferi that enables the spirochete to evade a mammalian host's immune response.
The lipoprotein, VlsE, is encoded by the variable major protein (VMP)-like sequence (vls) locus, Dr. James C. Sacchettini and associates report in the June 14th issue of the Journal of Biological Chemistry.
It is believed that VlsE plays an important role in mammalian infection because loss of the plasmid that encodes this protein results in reduced infectivity of the bacterium, the researchers explain. While VlsE induces a strong antibody response in infected mammals, rapid antigenic variation is believed to promote immune evasion.
Previous research in mice has shown that sequence changes are present within 4 days of infection, and by 28 days "every isolate from skin or other tissues is unique and contains roughly 9 to 13 recombination events," Dr. Sacchettini's team points out.
To investigate "the relationship between VlsE structure and antigenicity," Dr. Sacchettini, of Texas A&M University in College Station, and his colleagues examined the VlsE1 variant of B. burgdorferi by X-ray crystallography to elucidate its three-dimensional structure.
They found that six variable regions of VlsE form loop structures around predominantly invariant portions of the protein. "The surface localization of the variable amino acid segments appears to protect the conserved regions from interaction with antibodies and hence may contribute to immune evasion," they report.
In a university statement, Dr. Sacchettini stated, "these structures provide a roadmap to the development of new diagnostics as well as effective vaccines."
J Biol Chem 2002;277:21691-21696.