A heptad motif of leucine residues found in membrane proteins can drive self-assembly of artificial transmembrane segments

Specific interactions between cu-helical transmembrane segments are importa nt for folding and/or oligomerization of membrane proteins. Previously, we have shown that most transmembrane helix-helix interfaces of a set of cryst allized membrane proteins are structurally equivalent to soluble leucine zi pper interaction domains. To establish a simplified model of these membrane -spanning leucine zippers, we studied the homophilic interactions of artifi cial transmembrane segments using different experimental approaches. Import antly, an oligoleucine, but not an oligoalanine, sequence efficiently self- assembled in membranes as well as in detergent solution. Self-assembly was maintained when a leucine zipper type of heptad motif consisting of leucine residues was grafted onto an alanine host sequence. Analysis of point muta nts or of a random sequence confirmed that the heptad motif of leucines med iates self-recognition of our artificial transmembrane segments. Further, a data base search identified degenerate versions of this leucine motif with in transmembrane segments of a variety of functionally different proteins. For several of these natural transmembrane segments, self-interaction was e xperimentally verified. These results support various lines of previously r eported evidence where these transmembrane segments were implicated in the oligomeric assembly of the corresponding proteins.