Photoreactive labeling of M13 coat protein in model membranes by use of a glycolipid probe.

Coliphage M13 coat protein in synthetic bilayer membranes was labeled by use of 12-(4-azide-2-nitrophenoxy)stearoyl[1-14C]glucosamine, a photoreactive glycolipid probe that spontaneously inserts into membranes. In this model system, the probe preferentially labeled the proteins over the lipids. Experiments designed to test the probe's restriction to integral membrane proteins revealed that extrinsic proteins as well as external peptide fragments of integral membrane proteins were not accessible to the photogenerated nitrene on the fatty acid chain. Only integral membrane peptides were labeled by the membrane-bound probe. These results indicate that protein labeling can be effected specifically from within the hydrocarbon milieu of a model membrane system.