The composition rather than position of polar residues (QxxS) drives aspartate receptor transmembrane domain dimerization in vivo.
Transmembrane (TM) helix association is an important process affecting the function of many integral membrane proteins. Consequently, aberrations in this process are associated with diseases. Unfortunately, our knowledge of the factors that control this oligomerization process in the membrane milieu is limited at best. Previous studies have shown a role for polar residues in the assembly of synthetic peptides in vitro and the association of de novo-designed TM helices in vivo. Here we examined, for the first time, the involvement of polar residues in the dimerization of a biological TM domain in its natural environment. We analyzed both the involvement of polar residues in the dimerization process and whether their influence is position-dependent. For this purpose, we used the TM domain of the Escherichia coli aspartate receptor (Tar) and 10 single and double mutants. Polar to nonpolar mutations in the sequence demonstrated the role of the QxxS motif in the dimerization of the Tar TM domain. Moreover, creating a GxxxG motif, instead of the polar motif, almost completely abolished dimerization. Swapping positions between two wild-type polar residues did not affect dimerization, implying a similar contribution from both positions. Interestingly, mutants that contain two identical strong polar residues, EE and QQ, demonstrated a substantially higher level of dimerization than a QE mutant, although all three TM domains contain two strong polar residues. This result suggests that, in addition to the polarity of the residues, the formation of symmetric bonds also plays a role in dimer stability. The results of this study may facilitate a rational modulation of membrane protein function for therapeutic purposes.
Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel.
Neta
N
Sal-Man
Doron
D
Gerber
Yechiel
Y
Shai
D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D001224:Aspartic Acid / Q000737:chemistry*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D002628:Chemoreceptor Cells; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics; D005973:Glutamine / Q000737:chemistry* / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D033902:Periplasmic Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D017459:Receptors, Amino Acid / Q000737:chemistry* / Q000235:genetics; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics; D012694:Serine / Q000737:chemistry* / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D008565:Membrane Proteins; D033902:Periplasmic Binding Proteins; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C057331:Tar protein, E coli; D014157:Transcription Factors; C031959:aspartic acid receptor; C066719:toxR protein, bacteria; D005973:Glutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; D012694:Serine