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Smirnova et al. 10.1073/pnas.0708258104. |
Fig. 6. Comparison of proposed outward-facing conformation of LacY (1) with the structure of EmrD (PDB ID: 2GFP) (2). EmrD, like LacY, belongs to the MFS family and has a similar overall fold, with 12 transmembrane helices symmetrically organized into N- and C-terminal six-helix bundles. However, EmrD is closed on the cytoplasmic side. (A) PDB coordinates of EmrD (colored light brown) are superimposed on the outward-facing model for LacY (colored blue). Transmembrane helices are indicated. View from the cytoplasmic side showing close proximity of the ends of helices II-III and IV-V to the ends of helices X-XI where double-cysteine pairs are engineered. Ca atoms of the residues 73, 136, 137, 340, and 401 are shown as spheres with dashed lines connecting pairs used for DEER measurements. Part of the central loop between helices VI-VII and the C-terminal tail is removed for clarity. (B) Cytoplasmic view of the inward-facing conformer of LacY (PDB ID: 1PV6) is shown on the same scale to demonstrate the predicted magnitudes of the distance changes.
1. Abramson J, Smirnova I, Kasho V, Verner G, Kaback HR, Iwata S (2003) Science 301:610-615.
2. Yin Y, He X, Szewczyk P, Nguyen T, Chang G (2006) Science 312:741-744.
Movie 1. The movie illustrates the transport cycle through the membrane catalyzed by LacY, which involves coupled symport of one sugar molecule and one H+ from periplasmic space into cytoplasm using the H+ electrochemical gradient (interior negative and/or alkaline) as the driving force. Binding of the H+ to the H+-translocating site increases the open probability of LacY on the periplasmic side and binding of the sugar to the outward-facing conformation. Sugar binding induces a global conformational change that results in an inward-facing conformation and sugar release to the cytoplasm. Dissociation of the H+ completes the transport cycle. Animated movements are based on distances measured by DEER for solubilized LacY as described in the article.
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