Changing single side-chains can greatly enhance the resistance of a membrane protein to irreversible inactivation

The thermal inactivation rates of a set of 20 cysteine-substituted variants of the integral membrane protein diacylglycerol kinase were measured. Two Of the mutations, I53C and I70C, were found to significantly prolong the ha lf-life of the enzyme in detergent solution. By combining the single mutant s to create a double mutant, I53C/I70C, the half-life of the enzyme was imp roved from less than a minute at 70 degrees C to 51 minutes. These results demonstrate that individual side-chain substitutions can significantly impr ove the properties of membrane proteins in detergent solution. (C) 1999 Aca demic Press.