Improved low pH bicelle system for orienting macromolecules over a wide temperature range

We have prepared and characterized a novel bicelle system composed of 1,2-d i-O-dodecyl-sn-glycero-3-phosphocholine (DIODPC) and 3-(chloramidopropyl) d imethylammonio-2-hydroxyl-1-propane sulfonate (CHAPSO). At the optimal DIOD PC/CHAPSO molar ratio of 4.3:1, this medium becomes magnetically oriented f rom pH 6.5 down to pH 1.0. Unlike previously reported bicelle preparations, these bicelles are chemically stable at low pH and are capable of inducing protein alignment, as illustrated by the large residual dipolar couplings measured for rusticyanin from Thiobacillus ferrooxidans at pH 2.1. The DIOD PC/CHAPSO system is particularly useful for measuring residual dipolar coup lings of macromolecules that require very acidic conditions.