title: Interplay between hydrophobicity and the positive-inside rule in determining membrane-protein topology.
abstract: The energetics of membrane-protein interactions determine protein topology and structure: hydrophobicity drives the insertion of helical segments into the membrane, and positive charges orient the protein with respect to the membrane plane according to the positive-inside rule. Until recently, however, quantifying these contributions met with difficulty, precluding systematic analysis of the energetic basis for membrane-protein topology. We recently developed the dsTβL method, which uses deep sequencing and in vitro selection of segments inserted into the bacterial plasma membrane to infer insertion-energy profiles for each amino acid residue across the membrane, and quantified the insertion contribution from hydrophobicity and the positive-inside rule. Here, we present a topology-prediction algorithm called TopGraph, which is based on a sequence search for minimum dsTβL insertion energy. Whereas the average insertion energy assigned by previous experimental scales was positive (unfavorable), the average assigned by TopGraph in a nonredundant set is -6.9 kcal/mol. By quantifying contributions from both hydrophobicity and the positive-inside rule we further find that in about half of large membrane proteins polar segments are inserted into the membrane to position more positive charges in the cytoplasm, suggesting an interplay between these two energy contributions. Because membrane-embedded polar residues are crucial for substrate binding and conformational change, the results implicate the positive-inside rule in determining the architectures of membrane-protein functional sites. This insight may aid structure prediction, engineering, and design of membrane proteins. TopGraph is available online (topgraph.weizmann.ac.il).
authors: Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel;
authors: Assaf
authors: A
authors: Elazar
authors: Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel;
authors: Jonathan Jacob
authors: JJ
authors: Weinstein
authors: Bioinformatics and Biological Computing Unit, Weizmann Institute of Science, Rehovot 76100, Israel.
authors: Jaime
authors: J
authors: Prilusky
authors: Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel; sarel@weizmann.ac.il.
authors: Sarel Jacob
authors: SJ
authors: Fleishman
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000596:Amino Acids / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry* / Q000235:genetics; D003593:Cytoplasm / Q000737:chemistry / Q000235:genetics; D004734:Energy Metabolism / Q000235:genetics; D057927:Hydrophobic and Hydrophilic Interactions; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation
chemical_list: D000596:Amino Acids; D008565:Membrane Proteins
keywords: Bellman–Ford search; membrane insertion; positive-inside rule; topology prediction