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.