The Low Polarity of Many Membrane Proteins

TLDR

The polarities of a large number of soluble and membrane proteins were calculated by summing the mole fractions of polar amino acids. The study found that 85 % of 205 soluble proteins had polarities of 47 ± 6 %, only 2 % fell below 40 %, whereas 47 % of 19 membrane proteins were below 40 %, indicating that most intrinsic membrane proteins are low‑polarity and that the polarity index is a useful characterization parameter.

Abstract

The polarities of a large number of soluble and membrane proteins have been calculated by summing the mole fractions of polar amino acids. It was found that 85% of the 205 soluble proteins considered in this study had polarities of 47 ± 6%. Only 2% of the soluble proteins had polarities below 40%, whereas 47% of the 19 membrane proteins had polarities below 40%. The membrane proteins with polarities below 40% could be separated from their respective membranes only by detergents or organic solvents, indicating the importance of hydrophobic forces in their interaction with other membrane components. It is concluded that the majority of “intrinsic” membrane proteins have low polarity, and that the polarity index is therefore a useful parameter for characterization of membrane proteins.