title: Specificity in transmembrane helix-helix interactions mediated by aromatic residues.
abstract: Aromatic residues have been previously shown to mediate the self-assembly of different soluble proteins through pi-pi interactions (McGaughey, G. B., Gagne, M., and Rappe, A. K. (1998) J. Biol. Chem. 273, 15458-15463). However, their role in transmembrane (TM) assembly is not yet clear. In this study, we performed statistical analysis of the frequency of occurrence of aromatic pairs in a bacterial TM data base that provided an initial indication that the appearance of a specific aromatic pattern, Aromatic-XX-Aromatic, is not coincidental, similar to the well characterized QXXS motif. The QXXS motif was previously shown to be both critical and sufficient for stabilizing TM self-assembly. Using the ToxR system, we monitored the dimerization propensities of TM domains that contain mutations of interacting residues to aromatic amino acids and demonstrated that aromatic residues can adequately stabilize self-association. Importantly, we have provided an example of a natural TM domain, the cholera toxin secretion protein EpsM, whose TM self-assembly is mediated by an aromatic motif (WXXW). This is, in fact, the first evidence that aromatic residues are involved in the dimerization of a wild type TM domain. The association mediated by aromatic residues was found to be sensitive to the TM sequence, suggesting that aromatic residue motifs can provide a general means for specificity in TM assembly. Molecular dynamics provided a structural explanation for this backbone sequence sensitivity.
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Neta
authors.initials: N
authors.lastname: Sal-Man
authors.forename: Doron
authors.initials: D
authors.lastname: Gerber
authors.forename: Itai
authors.initials: I
authors.lastname: Bloch
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Shai
mesh_terms: D020816:Amino Acid Motifs; D024322:Amino Acids, Aromatic / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014734:Vibrio cholerae / Q000235:genetics / Q000378:metabolism
chemical_list: D024322:Amino Acids, Aromatic; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C083759:EpsM protein, Vibrio cholerae; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C066719:toxR protein, bacteria