PMID:10448046
| Citation |
Wang, Q and Kaback, HR (1999) Proximity relationships between helices I and XI or XII in the lactose permease of Escherichia coli determined by site-directed thiol cross-linking. J. Mol. Biol. 291:683-92 |
|---|---|
| Abstract |
The lactose permease of Escherichia coli was expressed in two fragments (split permease), each with a Cys residue, and cross-linking was studied. Split permease with a discontinuity in either loop II/III (N2C10permease) or loop VI/VII (N6C6permease) was used. Proximity of multiple pairs of Cys residues in helices I and XI or XII was examined by using three homobifunctional thiol-specific cross-linking reagents of different lengths and flexibilities (6 A, rigid; 10 A, rigid; 16 A, flexible) or iodine. Cys residues in the periplasmic half of helix I cross-link to Cys residues in the periplasmic half of helix XI. In contrast, no cross-linking is evident with paired Cys residues near the cytoplasmic ends of helices I and XI. Therefore, the periplasmic halves of helices I and XI are in close proximity, and the helices tilt away from each other towards the cytoplasmic face of the membrane. Cross-linking is also found with paired Cys residues near the middle of helices I and XII, but not with paired Cys residues near either end of the helices. Thus, helices I and XII are in close proximity only in the approximate middle of the membrane. Based on the findings, a modified helix packing model is proposed. |
| Links |
PubMed Online version:10.1006/jmbi.1999.2948 |
| Keywords |
Biological Transport, Active; Cross-Linking Reagents; Cysteine/chemistry; Escherichia coli/enzymology; Escherichia coli/genetics; Escherichia coli Proteins; Lactose/metabolism; Maleimides; Membrane Transport Proteins/chemistry; Membrane Transport Proteins/genetics; Membrane Transport Proteins/metabolism; Models, Molecular; Monosaccharide Transport Proteins; Mutagenesis, Site-Directed; Protein Structure, Secondary; Sulfhydryl Compounds/chemistry; Symporters |
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