Abstract:
:The pKa values of ionizable groups that lie between the active site region of bacteriorhodopsin (bR) and the extracellular surface of the protein are reported. Glu-204 is found to have an elevated pKa in the resting state of bR, suggesting that it corresponds to the proton-releasing group in bR. Its elevated pKa is predicted to be due in part to strong repulsive interactions with Glu-9. Following trans-cis isomerization of the retinal chromophore and the transfer of a proton to Asp-85, polar groups on the protein are able to interact more strongly with the ionized state of Glu-204, leading to a substantial reduction of its pKa. This suggests a general mechanism for proton release in which isomerization and subsequent charge separation initially produce a new electrostatic balance in the active site of bR. Here it is proposed that those events in turn drives a conformational change in the protein in which the ionized state of Glu-204 can be stabilized through interactions with groups that were previously inaccessible. Whether these groups should be identified with polar moieties in the protein, bound waters, or Arg-82 is an important mechanistic question whose elucidation will require further study.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Sampogna RV,Honig Bdoi
10.1016/S0006-3495(96)79320-7subject
Has Abstractpub_date
1996-09-01 00:00:00pages
1165-71issue
3eissn
0006-3495issn
1542-0086pii
S0006-3495(96)79320-7journal_volume
71pub_type
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