A Heptad Motif of Leucine Residues Found in Membrane Proteins Can Drive Self-assembly of Artificial Transmembrane Segments*
- From the Universität Heidelberg, Neurobiology Department, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
Abstract
Specific interactions between α-helical transmembrane segments are important for folding and/or oligomerization of membrane proteins. Previously, we have shown that most transmembrane helix-helix interfaces of a set of crystallized membrane proteins are structurally equivalent to soluble leucine zipper interaction domains. To establish a simplified model of these membrane-spanning leucine zippers, we studied the homophilic interactions of artificial transmembrane segments using different experimental approaches. Importantly, an oligoleucine, but not an oligoalanine, se- quence 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 mutants or of a random sequence confirmed that the heptad motif of leucines mediates self-recognition of our artificial transmembrane segments. Further, a data base search identified degenerate versions of this leucine motif within transmembrane segments of a variety of functionally different proteins. For several of these natural transmembrane segments, self-interaction was experimentally verified. These results support various lines of previously reported evidence where these transmembrane segments were implicated in the oligomeric assembly of the corresponding proteins.
Footnotes
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↵* This work was supported by Deutsche Forschungsgemeinschaft (Grant La699/4–1 and Heisenberg Program) and the Fonds der Chemischen Industrie.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence and reprint requests should be addressed: Institut für Neurobiologie, Uni Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany. Tel.: 06221-548696; Fax: 06221-544496; E-mail: Langosch{at}sun0.urz.uni-heidelberg.de.
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↵2 O. Huber, R. Kemler, and D. L., manuscript submitted.
- Abbreviations:
- TMS
-
transmembrane segment
- CHAPS
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3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonic acid
- EpoR
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erythropoietin receptor
- MalE
-
maltose-binding protein
- MU
-
Miller units
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- Received October 2, 1998.
- Revision received January 15, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
