The NOP-1 gene from the eukaryote Neurospora crassa, a filamentous fungus, has recently been shown to encode an archaeal rhodopsin–like protein NOP-1. To explore the functional mechanism of NOP-1 and its possible similarities to archaeal and visual rhodopsins, static and time-resolved Fourier transform infrared difference spectra were measured from wild-type NOP-1 and from a mutant containing an Asp→Glu substitution in the Schiff base (SB) counterion, Asp131 (D131E). Several conclusions could be drawn about the molecular mechanism of NOP-1: (1) the NOP-1 retinylidene chromophore undergoes an all-trans to 13-cis isomerization, which is typical of archaeal rhodopsins, and closely resembles structural changes of the chromophore in sensory rhodopsin II; (2) the NOP-1 SB counterion, Asp131, has a very similar environment and behavior compared with the SB counterions in bacteriorhodopsin (BR) and sensory rhodopsin II; (3) the O–H stretching of a structurally active water molecule(s) in NOP-1 is similar to water detected in BR and is most likely located near the SB and SB counterion in these proteins; and (4) one or more cysteine residues undergo structural changes during the NOP-1 photocycle. Overall, these results indicate that many features of the active sites of the archaeal rhodopsins are conserved in NOP-1, despite its eukaryotic origin.
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1 September 2002
A Fourier Transform Infrared Study of Neurospora Rhodopsin: Similarities with Archaeal Rhodopsins
Vladislav Bergo,
Elena N. Spudich,
John L. Spudich,
Kenneth J. Rothschild
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Photochemistry and Photobiology
Vol. 76 • No. 3
September 2002
Vol. 76 • No. 3
September 2002