In the present communication, we introduce a novel concept in multispanning polytopic membrane proteins revealed by the study of the band 3 protein. The transmembrane domain of such proteins can be divided into three categories, that is, hydrophilic loops connecting transmembrane peptides (category 1), portions embedded by peptide-peptide interactions (category 2), and portions embedded by peptide-lipid interactions (category 3). Category 2 peptides of polytopic membrane proteins were found to stably reside in the lipid bilayer without peptide-lipid interactions that had been thought to be essential for transmembrane segments. Category 3 peptides are equivalent to single-spanning segments of bitopic membrane proteins. Three different experiments, namely proteolytic digestion, chemical modification of the band 3 protein, and cell free transcription and translation, were used to categorize the transmembrane peptides.Key words: band 3 protein, transmembrane (TM) peptide, classification of TM, category 2-TM, polytopic membrane protein.
Interfacial Anchor Properties of Tryptophan Residues in Transmembrane Peptides Can Dominate over Hydrophobic Matching Effects in Peptide−Lipid Interactions†
