A turn propensity scale for transmembrane helices

Using a model protein with a 40 residue hydrophobic transmembrane segment, we have measured the ability of all the 20 naturally occurring amino acids to form a tight turn when placed in the middle of the hydrophobic segment. Turn propensities in a transmembrane helix are found to be markedly differe nt from those of globular proteins, and in most cases correlate closely wit h the hydrophobicity of the residue. The turn propensity scale may be used to improve current methods for membrane protein topology prediction. (C) 19 99 Academic Press.