Abstract:
:The photocycle of the photophobic receptor from Natronobacterium pharaonis, NpSRII, is studied by static and time-resolved step-scan Fourier transform infrared spectroscopy. Both low-temperature static and time-resolved spectra resolve a K-like intermediate, and the corresponding spectra show little difference within the noise of the time-resolved data. As compared to intermediate K of bacteriorhodopsin, relatively large amide I bands indicate correspondingly larger distortions of the protein backbone. The time-resolved spectra identify an intermediate L-like state with surprisingly small additional molecular alterations. With the formation of intermediate M, the Schiff-base proton is transferred to the counterion Asp-75. This state is characterized by larger amide bands indicating larger distortions of the protein. We can identify a second M state that differs only in small-protein bands. Reisomerization of the chromophore to all-trans occurs with the formation of intermediate O. The accelerated decay of intermediate M caused by azide results in another red-shifted intermediate with a protonated Schiff base. The chromophore in this state, however, still has 13-cis geometry. Nevertheless, the reisomerization is still as slow as under the conditions without azide. The results are discussed with respect to mechanisms of the observed proton pumping and the possible roles of the intermediates in receptor activation.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Hein M,Wegener AA,Engelhard M,Siebert Fdoi
10.1016/S0006-3495(03)74935-2subject
Has Abstractpub_date
2003-02-01 00:00:00pages
1208-17issue
2 Pt 1eissn
0006-3495issn
1542-0086pii
S0006-3495(03)74935-2journal_volume
84pub_type
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