Charge-Charge Interactions Promote Transmembrane Helix-Helix Association Depending on Sequence Context

Abstract

Folding and oligomerization of integral membrane proteins frequently depend on specific interactions of transmembrane helices. Interacting amino acids of helix-helix interfaces may form complex motifs and exert different types of molecular forces (Herrmann et al., 2009; Langosch and Arkin, 2009; Unterreitmeier et al., 2007). Here, a set of strongly self-interacting transmembrane domains, as isolated from a combinatorial library, was found to contain basic and acidic residues in combination with polar non-ionizable amino acids and C-terminal GxxxG motifs. Mutational analyses of selected sequences and reconstruction of high-affinity interfaces confirmed cooperation of these residues in homotypic interaction. Probing heterotypic interaction indicated the presence of interhelical charge-charge interactions. Further, simple motifs of an ionizable residue and GxxxG are significantly overrepresented in natural transmembrane domains and a specific combination of these motifs exhibits high-affinity heterotypic interaction. We conclude that intramembrane charge-charge interactions depend on sequence context. Moreover, they appear important for homo- and heterotypic interactions of numerous natural transmembrane domains.Herrmann, J., J. Panitz, S. Unterreitmeier, A. Fuchs, D. Frishman, and D. Langosch. 2009. Complex patterns of histidine, hydroxylated amino acids and the GxxxG motif mediate high-affinity transmembrane domain interactions. J. Mol. Biol. 385:912-923.Langosch, D., and I.T. Arkin. 2009. Interaction and Conformational Dynamics of Membrane-Spanning Protein Helices. Protein Sci. 18:1343-1358.Unterreitmeier, S., A. Fuchs, T. Schaffler, R.G. Heym, D. Frishman, and D. Langosch. 2007. Phenylalanine Promotes Interaction of Transmembrane Domains via GxxxG Motifs. J. Mol. Biol. 374:705-718.