Abstract：
:The proteorhodopsin family consists of retinal proteins of marine bacterial origin with optical properties adjusted to their local environments. For green proteorhodopsin, a highly specific mutation in the EF loop, A178R, has been found to cause a surprisingly large redshift of 20 nm despite its distance from the chromophore. Here, we analyze structural and functional consequences of this EF loop mutation by time-resolved optical spectroscopy and solid-state NMR. We found that the primary photoreaction and the formation of the K-like photo intermediate is almost pH-independent and slower compared to the wild-type, whereas the decay of the K-intermediate is accelerated, suggesting structural changes within the counterion complex upon mutation. The photocycle is significantly elongated mainly due to an enlarged lifetime of late photo intermediates. Multidimensional MAS-NMR reveals mutation-induced chemical shift changes propagating from the EF loop to the chromophore binding pocket, whereas dynamic nuclear polarization-enhanced (13)C-double quantum MAS-NMR has been used to probe directly the retinylidene conformation. Our data show a modified interaction network between chromophore, Schiff base, and counterion complex explaining the altered optical and kinetic properties. In particular, the mutation-induced distorted structure in the EF loop weakens interactions, which help reorienting helix F during the reprotonation step explaining the slower photocycle. These data lead to the conclusion that the EF loop plays an important role in proton uptake from the cytoplasm but our data also reveal a clear interaction pathway between the EF loop and retinal binding pocket, which might be an evolutionary conserved communication pathway in retinal proteins.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Mehler M,Scholz F,Ullrich SJ,Mao J,Braun M,Brown LJ,Brown RC,Fiedler SA,Becker-Baldus J,Wachtveitl J,Glaubitz Cdoi
10.1016/j.bpj.2013.06.014subject
Has Abstractpub_date
2013-07-16 00:00:00pages
385-97issue
2eissn
0006-3495issn
1542-0086pii
S0006-3495(13)00692-9journal_volume
105pub_type
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