Structure and Mechanism of the Lactose Permease of Escherichia coli
Jeff Abramson,1 Irina Smirnova,3 Vladimir Kasho,3 Gillian Verner,3 H. Ronald Kaback,3* So Iwata1,2* Science. 2003 Aug 1;301(5633):610-5.
Membrane transport proteins that transduce free energy stored in electrochemical ion gradients into a concentration gradient are a major class of membrane proteins. We report the crystal structure at 3.5 angstroms of the Escherichia coli lactose permease, an intensively studied member of the major facilitator superfamily of transporters. The molecule is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the permease. A large internal hydrophilic cavity open to the cytoplasmic side represents the inward-facing conformation of the transporter. The structure with a bound lactose homolog, -D-galactopyranosyl-1-thio--D-galactopyranoside, reveals the sugar-binding site in the cavity, and residues that play major roles in substrate recognition and proton translocation are identified. We propose a possible mechanism for lactose/proton symport (cotransport) consistent with both the structure and a large body of experimental data.
2000年教科书GLUT1动态机理如下。 不少喇叭口。小颜只需用这个吧。再说她没说发现机理。她搞定了晶体及更详细结构。看来看去是风车大战。
Model of the mechanism of uniport transport by GLUT1, which is believed to shuttle between two conformational states
In one conformation (?1?, ?2?, and ?5?), the glucose-binding site faces outward; in the other (?3?, ?4?), the binding site faces inward. Binding of glucose to the outward-facing binding site (?1? →? 2?) triggers a conformational change in the transporter (?2? →? 3?), moving the bound glucose through the protein such that it is now bound to the inward-facing binding site. Glucose can then be released to the inside of the cell (?3? → ?4?). Finally, the transporter undergoes the reverse conformational change (?4? →? 5?), inactivating the inward-facing glucose binding site and regenerating the outward-facing one. If the concentration of glucose is higher inside the cell than outside, the cycle will work in reverse (?4? →??1?), catalyzing net movement of glucose from inside to out.
From: Section 15.3, Uniporter-Catalyzed Transport
Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
JessAB 发表评论于
回复 'Fanreninus' 的评论 :
有什么大不了的? 幽默一把.
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幽默感去哪了?
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UCLA. 他的homepage说出了结构（0.7%已知）的重要性。
Research Interests:
Membrane transport proteins are responsible for many critical biological functions including governing energy transduction, modifying ion concentrations, and actively importing metabolites into the cell. Membrane proteins represent 20-30% of all proteins in each of the sequenced genomes. In addition, they are targets for 50% of all marketed drugs. Considering their biological and pharmacological relevance and their vast numbers throughout genomes, there is an enormous demand for structural information. However, membrane proteins represent only about ~0.7% of the protein structures in the Protein data bank. The reason for this discrepancy stems from the hydrophobic nature of membrane proteins, which reside in a phospholipid bilayer, making them difficult to express, purify, and crystallize.
Our lab is trying to overcome these barriers and resolve the structures of several channels and transporters. This is an ideal format for students to interact with other groups and learn numerous techniques through interdepartmental collaborations.
Representative Publications:
Ujwal R, Cascio D, Colletier JP, Faham S, Zhang J, Toro L, Ping P, Abramson J (2008). The crystal structure of mouse VDAC1 at 2.3 A resolution reveals mechanistic insights into metabolite gating. Proc Natl Acad Sci U S A. Nov 18;105(46):17742-7.
Faham S, Watanabe A, Besserer GM, Cascio D, Specht A, Hirayama BA, Wright EM, Abramson J (2008). The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport. Science. Aug 8;321(5890):810-4.
Abramson J, Smirnova I, Kasho V, Verner G, Kaback HR, Iwata S. (2003). Structure and mechanism of the lactose permease of Escherichia coli. Science. 301(5633):610-5.
