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Structure–function relationships of integral membrane proteins: Membrane transporters vs channels
Author(s) -
le Coutre Johannes,
Kaback H. Ronald
Publication year - 2000
Publication title -
peptide science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/1097-0282(2000)55:4<297::aid-bip1003>3.0.co;2-h
Subject(s) - lactose permease , kcsa potassium channel , chemistry , symporter , permease , electrochemical gradient , integral membrane protein , membrane biology , biophysics , membrane transport protein , lac repressor , membrane , membrane protein , transporter , biochemistry , ion channel , escherichia coli , lac operon , receptor , biology , gene
Escherichia coli lactose permease, a paradigm for membrane transport proteins, and Streptomyces lividans KcsA, a paradigm for K + channels, are compared on the level of structure, dynamics, and function. The homotetrameric channel, which allows the downhill movement of K + with an electrochemical gradient, is relatively rigid and inflexible, as observed by Fourier transform infrared spectroscopy. Lactose permease catalyzes transduction of free energy stored in an electrochemical H + gradient into work in the form of a concentration gradient. In marked contrast to KcsA, the permease exhibits a high degree of H/D exchange, in addition to enhanced sensitivity to lateral lipid packing pressure, thereby indicating that this symport protein is extremely flexible and conformationally active. Finally, the differences between lactose permease and KcsA are discussed in the context of their specific functions with particular emphasis on differences between coupling in symport proteins and gating in channels. © 2001 John Wiley & Sons, Inc. Biopolymers (Pept Sci) 55: 297–307, 2000