FINE-TUNING THE TOPOLOGY OF A POLYTOPIC MEMBRANE-PROTEIN - ROLE OF POSITIVELY AND NEGATIVELY CHARGED AMINO-ACIDS

The effects of positively and negatively charged residues on the membrane topology of a model E. coli protein with two transmembrane segments have been studied. We show that addition or removal of as little as a single positively charged lysine residue in one of two critical regions can be sufficient to reverse the transmembrane topology of the molecule from Nout-Cout to Nin-Cin. Negatively charged residues are much less potent and significantly affect the topology only if present in high numbers. Finally, we provide data to suggest that sec-independent and sec-dependent translocation mechanisms differ in their sensitivity to positively charged amino acids. © 1990.