Surface-Active Helices in Transmembrane Proteins

Amphipathic surface-active helices enable peripheral proteins to perform a variety of important cellular functions such as: lipid association and transport, membrane perturbation and disruption in programmed cell death or antimicrobial activity, and signal transduction. Amphipathic helices that adopt a surface-active membrane location are also found in transmembrane proteins. Since they possess similar amino acid composition and therefore chemical and physical properties, it seems intuitively obvious that the specific role of these surface seeking, or horizontal helices in membrane spanning proteins in some ways parallel those of their cousins in peripheral proteins. This review compares research literature and data from both proteins sets (peripheral proteins and transmembrane) to examine this assumption. Furthermore, since the occurrence of surface-active / seeking helices in transmembrane protein structure is often omitted from comment in the literature, a brief survey of their apparent roles in transmembrane protein / lipid stabilization, microenvironment enclosure and signal transduction is offered here.