Molecule of the Month |
The Structure of Bovine Rhodopsin |
Activation of G-protein coupled receptors (GPCRs) is not yet understood. A recent crystal structure showed most of rhodopsin in the ground (not activated) state of the GPCR (Palczewski et al., 2000), but the cytoplasmic face, which couples to the G protein in signal transduction, was not well defined. We have determined an experimental three-dimensional structure for rhodopsin in the unactivated state, which shows good agreement wih the crystal struture in the transmembrane domain. This new structrue defines the cytoplasmic face in the activated (metarhodopsin II) receptor. Differences between the two structures suggest how the receptor is activated to couple with transducin. |
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We used the same approach to structrue as was used for bacteriorhodopsin. A series of overlapping peptides was synthesized that spans the sequence of the protein (left figure). Structures were determined for these peptides in solution by NMR. Helices formed helices and turns formed turns. Structure of some of the helices are presented below, overlayed on the corrsponding regions of the crystal structrue of rhodopsin (the peptide structures were determined prior to the publication of the crystal structure). Excellent agreement was observed with the crystal structure. |
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These peptides were assembled into a construct corresponding to the entire sequence of rhodopsin as shown for in the movie on the right.
Onto this construct were written (in MD program SYBYL) all the constraints from the peptide structrues and many distance constraints from other experiments on the intact protein (see reference). This was then subjected to simmulated annealing. |
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The structure obtained showed good agreement with the crystal structrue. Our structrue is in red and the crystal structure is in grenn and the retinal is in pink or blue. Our structure has good data density in the cytoplasmic face, which the crystal structure does not, while our structure is weak in the extracellular (intradiskal) face while the crystal structure is well defined in that region. The two structures are virtually indistinguishable in the transmembrane regions.
To learn more about rhodopsin & Yeagle's research projects please follow this link. |
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Reference:
"Studies on the structure of the G-protein coupled receptor rhodopsin including the putative G-protein binding site in unactivated forms", Philip Yeagle, Gregory Choi, & Arlene D. Albert. Biochemistry 40, 11932-11937 (2001). |
