| Title: | Protein-assisted pericyclic reactions: an alternate hypothesis for the action of quantal receptors |
| Author(s): | Radding W; Romo T; Phillips GN; |
| Address: | "Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA. radding@bioc.rice.edu" |
| DOI: | 10.1016/S0006-3495(99)77125-0 |
| ISSN/ISBN: | 0006-3495 (Print) 1542-0086 (Electronic) 0006-3495 (Linking) |
| Abstract: | "The rules for allowable pericyclic reactions indicate that the photoisomerizations of retinals in rhodopsins can be formally analogous to thermally promoted Diels-Alder condensations of monoenes with retinols. With little change in the seven-transmembrane helical environment these latter reactions could mimic the retinal isomerization while providing highly sensitive chemical reception. In this way archaic progenitors of G-protein-coupled chemical quantal receptors such as those for pheromones might have been evolutionarily plagiarized from the photon quantal receptor, rhodopsin, or vice versa. We investigated whether the known structure of bacteriorhodopsin exhibited any similarity in its active site with those of the two known antibody catalysts of Diels-Alder reactions and that of the photoactive yellow protein. A remarkable three-dimensional motif of aromatic side chains emerged in all four proteins despite the drastic differences in backbone structure. Molecular orbital calculations supported the possibility of transient pericyclic reactions as part of the isomerization-signal transduction mechanisms in both bacteriorhodopsin and the photoactive yellow protein. It appears that reactions in all four of the proteins investigated may be biological analogs of the organic chemists' chiral auxiliary-aided Diels-Alder reactions. Thus the light receptor and the chemical receptor subfamilies of the heptahelical receptor family may have been unified at one time by underlying pericyclic chemistry" |
| Keywords: | "Animals Antibodies/chemistry Bacterial Proteins/chemistry/radiation effects Bacteriorhodopsins/chemistry/radiation effects Binding Sites Biophysical Phenomena Biophysics Models, Chemical Models, Molecular Photochemistry *Photoreceptors, Microbial Protein;" |
| Notes: | "MedlineRadding, W Romo, T Phillips, G N Jr eng 1T15ML07093/PHS HHS/ Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Research Support, U.S. Gov't, P.H.S. 1999/12/10 Biophys J. 1999 Dec; 77(6):2920-9. doi: 10.1016/S0006-3495(99)77125-0" |
