Conformational change in bacterio-opsin on binding to retinal.
The detailed mechanism of retinal binding to bacterio-opsin is important to understanding retinal pigment formation as well as to the process of membrane protein folding. We have measured the temperature dependence of bacteriorhodopsin formation from bacterio-opsin and all-trans retinal. An Arrhenius plot of the apparent second-order rate constants gives an activation energy of 11.6 +/- 0.7 kcal/mol and an activation entropy of -4 +/- 2 cal/mol deg. Comparison of the activation entropy to model compound reactions suggests that chromophore formation in bacteriorhodopsin involves a substantial protein conformational change. Cleavage of the polypeptide chain between residues 71 and 72 has little effect on the activation energy or entropy, indicating that the connecting loop between helices B and C is not involved in this conformational change.
Renthal
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Division of Earth and Physical Sciences, University of Texas at San Antonio 78249, USA. rrenthal@utsa.edu
Alaniz
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C
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism*; D006217:Halobacterium / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding; D011487:Protein Conformation; D012172:Retinaldehyde / Q000378:metabolism*
D001436:Bacteriorhodopsins; C017827:bacterio-opsin; D012172:Retinaldehyde