Efficient and wash-free labeling of membrane proteins using engineered Npu DnaE split-inteins.

An efficient and wash-free method to conjugate a fluorescent tag to a target membrane protein is developed, using engineered Npu DnaE split-inteins. This approach allowed fast labeling while avoiding the strenuous synthesis of a long polypeptide. Two different modes of labeling, namely specific binding and covalent conjugation, are observed. The covalent labeling was monitored within 5 min, without background staining.