A Fourier transform infrared study of Neurospora rhodopsin: similarities with archaeal rhodopsins

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.     

Structural states of dictyostelium myosin

Myosin purified from Dictyostelium amoebae has approximately 10% by weight of RNA associated with it, unless specific steps (DEAE cellulose chromatography or RNase digestion) are taken to remove it. This RNA has significant effects on the structural states formed by the myosin at low ionic strength in the presence of Mg2+. Rapid precipitation of RNA-free myosin by dilution generates bipolar thick filaments (540 nm long, 33 nm thick), often with a bare zone and a 15-nm transverse repeat. Rapid precipitation of myosin with copurified RNA yields linear aggregates of bipolar filaments, showing some lateral association. Slow precipitation of RNA-free myosin by dialysis yields very long filaments or ribbons (greater than 5 micrometer, 30--60 nm wide) in which the myosin may be packed diagonally across the filament, similar to the "side-polar" aggregates formed by other nonmuscle myosins and by smooth muscle myosin (Craig R, Megerman J: J Cell Biol 75:990, 1977; Hinssen H, D'Haese J, Small JV, Sobieszek A: J Ultrastruct Res 64:282, 1978). Slow precipitation of myosin with copurified RNA generates linear filaments with repeat intervals of 290 and 650 nm. Other polyanions were tested for their effects on myosin aggregation. Total RNA and ribosomal RNA from Dictyostelium, when added to RNA-free myosin, also induced the extensive linear aggregation seen with the copurified RNA/myosin complex, although higher concentrations of RNA were required to obtain quantitatively the same effect. DNA and heparin were also effective inducers of linear aggregation, whereas homopolymers of nucleotides and of acidic or basic amino acids were poorly effective.     

Time domain investigation on vibrational dephasing and spectral diffusion in CO-doped solid N2

Infrared picosecond accumulated photon echo experiments have been performed for the first time, using the Orsay Free Electron Laser, on the v = 0-->v = 1 transition of CO in solid nitrogen. The vibrational dephasing time is found to be exceptionally long ( T2>/=120 ns) at low temperature. The analysis of the observed spectral diffusion leads one to assume different energy transfer mechanisms depending on the CO concentration.