Bacterial Enzyme Sortase Used to Create Novel Targeted Vaccines

The transpeptidase activity of the bacterial enzyme sortase can be used in a process known as "sortagging" to install modified peptides and protein-sized antigens onto antibody heavy chains to create a new generation of targeted vaccines.

Sortase refers to a group of prokaryotic enzymes that modify surface proteins by recognizing and cleaving a carboxyl-terminal sorting signal. For most substrates of sortase enzymes, the recognition signal consists of the motif LPXTG (leucine-proline-any amino acid-threonine-glycine), then a highly hydrophobic transmembrane sequence, then a cluster of basic residues such as arginine. Cleavage occurs between the threonine and glycine residues, with transient attachment through the threonine residue to the active site cysteine residue, followed by transpeptidation that attaches the protein covalently to the cell wall.

Investigators at the Whitehead Institute for Biomedical Research (Cambridge, MA, USA) reported in the January 7, 2013, online edition of the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) that they had used sortagging, which combines the precision of a genetically encoded tag with the specificity of an enzymatic reaction and the ease and chemical versatility of peptide synthesis, to create a vaccine against herpes virus by attaching peptide antigens from 19 known viral epitopes to a cell-specific antibody. Mice immunized with this "cocktail" vaccine displayed a 10-fold reduction in viral load upon challenge with live viruses as compared to naïve animals.

"Sortagging is remarkably specific and efficient," said first author Dr. Lee Kim Swee, a postdoctoral researcher at the Whitehead Institute for Biomedical Research. "We were able to create 50 different constructs (antibody-protein attachments), which would not have been feasible if we had relied on the more traditional approach of genetic fusion. This is proof of principle that one could in fact use sortagging on antibodies to easily attach a tailored set of antigens, toward which the immune system can be educated. This technique also helps us understand how to design better antibody-based vaccines."

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Whitehead Institute for Biomedical Research