Stephen A. Waschuk
University of Guelph
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Featured researches published by Stephen A. Waschuk.
Science | 2006
Valentyn I. Prokhorenko; Andrea M. Nagy; Stephen A. Waschuk; Leonid S. Brown; Robert R. Birge; R. J. Dwayne Miller
Optical control of the primary step of photoisomerization of the retinal molecule in bacteriorhodopsin from the all-trans to the 13-cis state was demonstrated under weak field conditions (where only 1 of 300 retinal molecules absorbs a photon during the excitation cycle) that are relevant to understanding biological processes. By modulating the phases and amplitudes of the spectral components in the photoexcitation pulse, we showed that the absolute quantity of 13-cis retinal formed upon excitation can be enhanced or suppressed by ±20% of the yield observed using a short transform-limited pulse having the same actinic energy. The shaped pulses were shown to be phase-sensitive at intensities too low to access different higher electronic states, and so these pulses apparently steer the isomerization through constructive and destructive interference effects, a mechanism supported by observed signatures of vibrational coherence. These results show that the wave properties of matter can be observed and even manipulated in a system as large and complex as a protein.
Biochimica et Biophysica Acta | 2008
So Young Kim; Stephen A. Waschuk; Leonid S. Brown; Kwang-Hwan Jung
Proteorhodopsin is photoactive 7-transmembrane protein, which uses all-trans retinal as a chromophore. Proteorhodopsin subfamilies are spectrally tuned in accordance with the depth of habitat of the host organisms, numerous species of marine picoplankton. We try to find residues critical for the spectral tuning through the use of random PCR mutagenesis and endogenous retinal biosynthesis. We obtained 16 isolates with changed color by screening in Escherichia coli with internal retinal biosynthesis system containing genes for beta-carotene biosynthesis and retinal synthase. Some isolates contained multiple substitutions, which could be separated to give 20 single mutations influencing the spectral properties. The color-changing residues are distributed through the protein except for the helix A, and about a half of the mutations is localized on the helices C and D, implying their importance for color tuning. In the pumping form of the pigment, absorption maxima in 8 mutants are red-shifted and in 12 mutants are blue-shifted compared to the wild-type. The results of flash-photolysis showed that most of the low pumping activity mutants possess slower rates of M decay and O decay. These results suggest that the color-tuning residues are not restricted to the retinal binding pocket, in accord with a recent evolutionary analysis.
Proceedings of the National Academy of Sciences of the United States of America | 2005
Stephen A. Waschuk; Arandi G. Bezerra; Lichi Shi; Leonid S. Brown
Biochemistry | 2004
Yuji Furutani; Arandi G. Bezerra; Stephen A. Waschuk; Masayo Sumii; Leonid S. Brown; Hideki Kandori
Biochemistry | 2005
Masayo Sumii; Yuji Furutani; Stephen A. Waschuk; Leonid S. Brown; Hideki Kandori
Science | 2007
Valentyn I. Prokhorenko; Andrea M. Nagy; Stephen A. Waschuk; Leonid S. Brown; Robert R. Birge; R. J. Dwayne Miller
Biochemistry | 2006
Yuji Furutani; Masayo Sumii; Ying Fan; Lichi Shi; Stephen A. Waschuk; Leonid S. Brown; Hideki Kandori
Seibutsu Butsuri | 2006
Yuji Furutani; Masayo Sumii; Ying Fan; Lichi Shi; Stephen A. Waschuk; Leonid S. Brown; Hideki Kandori
生物物理 | 2005
昌代 住井; 祐詞 古谷; Stephen A. Waschuk; Leonid S. Brown; 秀樹 神取
Seibutsu Butsuri | 2005
Masayo Sumii; Yuji Furutani; Stephen A. Waschuk; Leonid S. Brown; Hideki Kandori