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Journal of Experimental Biology, Vol 196, Issue 1 183-195, Copyright © 1994 by Company of Biologists
JOURNAL ARTICLES |
HR Kaback, S Frillingos, H Jung, K Jung, GG Prive, ML Ujwal, C Weitzman, J Wu and K Zen
Howard Hughes Medical Institute, Department of Physiology, University of California Los Angeles 90024-1662.
The lactose permease (lac) of Escherichia coli is a paradigm for membrane transport proteins. Encoded by the lacY gene, the permease has been solubilized, purified to homogeneity, reconstituted into phospholipid vesicles and shown to catalyse the coupled translocation of beta-galactosides and H+ with a stoichiometry of unity. Circular dichroism and other spectroscopic approaches demonstrate that the purified permease is about 80% helical. Based on hydropathy analysis of the primary amino-acid sequence, a secondary structure has been proposed in which the protein has 12 hydrophobic domains in alpha-helical conformation that traverse the membrane in zigzag fashion connected by hydrophilic loops. A variety of other approaches are consistent with the model and demonstrate that both the N and C termini are on the inner surface of the membrane, and studies on an extensive series of lac permease/alkaline phosphatase fusion proteins provide exclusive support for the topological predictions of the 12-helix motif. This presentation concentrates on the use of site-directed fluorescence spectroscopy to study structure-function relationships in the permease.
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 Y.-J. Seok, J. Sun, H. R. Kaback, and A. Peterkofsky Topology of allosteric regulation of lactose permease PNAS, December 9, 1997; 94(25): 13515 - 13519. [Abstract] [Full Text] [PDF]
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P. Braun, B. Persson, H. R. Kaback, and G. von Heijne Alanine Insertion Scanning Mutagenesis of Lactose Permease Transmembrane Helices J. Biol. Chem., November 21, 1997; 272(47): 29566 - 29571. [Abstract] [Full Text] [PDF]
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