Specific and covalent labeling of a membrane protein with organic fluorochromes and quantum dots

Bonasio, R.; Carman, C. V.; Kim, E.; Sage, P. T.; Love, K. R.; Mempel, T. R.; Springer, T. A.; von Andrian, U. H.

(2007 ), Volume: 104 , Issue: 34 , Pages: 14753-14758
The real-time observation of protein dynamics in living cells and organisms is of fundamental importance for understanding biological processes. Most approaches to labeling proteins exploit noncovalent interactions, unsuitable to long-term studies, or genetic fusion to naturally occurring fluorescent proteins that often have unsatisfactory optical properties. Here we used the fungal enzyme cutinase and its suicide substrate p-nitrophenyl phosphonate to covalently attach a variety of labels to the integrin lymphocyte function-associated antigen-1 (LFA-1) on the surface of living cells. Cutinase was embedded in the extracellular domain of LFA-1 with no appreciable influence on integrin function and conformational regulation. p-nitrophenyl phosphonate-conjugated fluorochromes, including the very bright and stable quantum dots, bound efficiently and specifically to LFA-1/cutinase. The availability of a genetically encoded tag that binds covalently to quantum dots could foster the development of new experimental strategies for the study of protein dynamics in vivo.
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