Suppressor scanning at positions 177 and 236 in the Escherichia coli lactose/H+ cotransporter and stereotypical effects of acidic substituents that suggest a favored orientation of transmembrane segments relative to the lipid bilayer.
Acidic substituents for Ala-177 (helix 6) or Tyr-236 (helix 7) in LacY cause effects on sugar recognition and cosubstrate coupling that are stereotypical of neutral substituents. Thus, helices 6 and 7 are probably oriented to produce little side-chain contact with the low dielectric lipid bilayer at positions 177 and 236.
King
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Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-0641, USA. steven.king@utmb.edu
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D002352:Carrier Proteins / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics; D009004:Monosaccharide Transport Proteins; D011487:Protein Conformation; D027981:Symporters
D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease