Topogenic signals in integral membrane proteins

Abstract

Integral membrane proteins are characterized by long apolar segments that cross the lipid bilayer. Polar domains flanking these apolar segments have a more balanced amino acid composition, typical for soluble proteins. We show that the apolar segments from three different kinds of membrane‐assembly signals do not differ significantly in amino acid content, but that the inside/outside location of the polar domains correlates strongly with their content of arginyl and lysyl residues, not only for bacterial inner‐membrane proteins, but also for eukaryotic proteins from the endoplasmic reticulum, the plasma membrane, the inner mitochondrial membrane, and the chloroplast thylakoid membrane. A positive‐inside rule thus seems to apply universally to all integral membrane proteins, with apolar regions targeting for membrane integration and charged residues providing the topological information. Copyright © 1988, Wiley Blackwell. All rights reserved