CAMBRIDGE, Mass.—Protein labeling has become an invaluable tool in understanding cell function, but the high-MW labels like GFP can perturb protein function while chemical modification methods lack the specificity of genetic tagging methods. Researchers at the Whitehead Institute of Biomedical Research recently tried to take the middle ground, using a chemoenzymatic labeling method the call sortagging.
As they describe in Nature Chemical Biology, sortagging relies on bacterial sortases, enzymes that covalently attach proteins to the bacterial cell wall via specific amino acid consensus sequences. Using S. aureus sortase A, which recognizes the LPXTG motif, the researchers were able to tag isolated soluble mouse MHC molecule genetically modified to carry the sequence LPETG near its C-terminus. They also found they could tag sequence-modified human CD154 proteins in both transfected-cell lysates and live cells, without labeling endogenous unmodified CD154 proteins.
"The multiplicity of sortases and their distinct recognition sequences, in principle, immediately expands the range of labeling possibilities to the simultaneous use of several uniquely tagged proteins and various probes in a single experimental setting," the authors write.
