Cytocompatible Modification of Thermoresponsive Polymers on Living Cells for Membrane Proteomic Isolation and Analysis

Efficient strategies for enriching and separating proteins are important and challenging for membrane proteomics. Many existing methods are caught in the dilemma of preserving maximal membrane proteins while avoiding the contamination of cytoplasmic proteins and organelles. Here, we report a polymer anchoring strategy for the selective preparation of membrane proteins through cell surface-initiated atom transfer radical polymerization. The cytocompatible polymerization strategy enables thermoresponsive poly( N-isopropylacrylamide) (pNIPPAm) chains to be grown from a specific protein on the surface of living cells. The polymer tagged membrane protein could be easily separated and enriched by thermoprecipitation. This method led to the identification of 1825 proteins of which 1036 (71.7%) were specific membrane proteins in E. coli. The separated proteins were identified by 2-DE and mass spectrometry. Among the 12 protein spots from the gel slice, eight were identified as outer membrane proteins. The described strategy opens up a new avenue for membrane protein enrichment and separation and may expedite the future development of membrane proteomics.