Helical sidedness and the distribution of polar residues in trans-membrane helices.

Trans-membrane helices have often been claimed to show "sidedness" in the distribution of polar and hydrophobic residues. However, an analysis of the statistical distribution of polar residues in randomly generated helices shows that the degree of bias commonly observed in real helices is far from statistically significant. It is concluded that "patchy" distributions of residues in such helices should be interpreted with great care.