1. Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
2. Stockholm Bioinformatics Center, AlbaNova, Stockholm University, SE-106 91 Stockholm, Sweden
3. Department of Physiology and Biophysics and the Center for Biomembrane Systems, University of California at Irvine, Irvine, California 92697-4560, USA
4. These authors contributed equally to this work.

Correspondence to: Gunnar von Heijne^1,2 Correspondence and requests for materials should be addressed to G.v.H. (Email: gunnar@dbb.su.se).

Abstract

Transmembrane -helices in integral membrane proteins are recognized co-translationally and inserted into the membrane of the endoplasmic reticulum by the Sec61 translocon. A full quantitative description of this phenomenon, linking amino acid sequence to membrane insertion efficiency, is still lacking. Here, using in vitro translation of a model protein in the presence of dog pancreas rough microsomes to analyse a large number of systematically designed hydrophobic segments, we present a quantitative analysis of the position-dependent contribution of all 20 amino acids to membrane insertion efficiency, as well as of the effects of transmembrane segment length and flanking amino acids. The emerging picture of translocon-mediated transmembrane helix assembly is simple, with the critical sequence characteristics mirroring the physical properties of the lipid bilayer.

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