Complexation of integral membrane proteins by phosphorylcholine-based amphipols.
Amphiphilic macromolecules, known as amphipols, have emerged as promising candidates to replace conventional detergents for handling integral membrane proteins in water due to the enhanced stability of protein/amphipol complexes as compared to protein/detergent complexes. The limited portfolio of amphipols currently available prompted us to develop amphipols bearing phosphorylcholine-based units (PC). Unlike carboxylated polymers, PC-amphipols remain soluble in aqueous media under conditions of low pH, high salt concentration, or in the presence of divalent ions. The solubilizing properties of four PC-amphipols were assessed in the case of two membrane proteins, cytochrome b(6)f and bacteriorhodopsin. The protein/PC-amphipol complexes had a low dispersity in size, as determined by rate zonal ultracentrifugation. Short PC-amphipols (<M> approximately 22 kDa) of low dispersity in length, containing approximately 30 mol% octyl side groups, approximately 35 mol% PC-groups, and approximately 35 mol% isopropyl side groups, appeared best suited to form stable complexes, preserving the native state of BR over periods of several days. BR/PC-amphipol complexes remained soluble in aqueous media at pH> or =5, as well as in the presence of 1 M NaCl or 12 mM calcium ions. Results from isothermal titration calorimetry indicated that the energetics of the conversion of BR/detergent complexes into BR/amphipol complexes are similar for PC-amphipols and carboxylated amphiphols.
Diab
C
C
Department of Chemistry and Faculty of Pharmacy, Université de Montréal, CP 6128 Succursale Centre Ville, Montreal QC, Canada.
Tribet
C
C
Gohon
Y
Y
Popot
J-L
JL
Winnik
F M
FM
D002151:Calorimetry; D003902:Detergents / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry*; D010767:Phosphorylcholine / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011437:Propylamines / Q000737:chemistry