TCBG Seminar

The Mechanism of Spectral Shift and Color tuning in Rhodopsins

Professor Marcus Elstner
University of Braunschweig

Thursday, August 10, 2006
3:00 pm (CT)
3169 Beckman Institute


The mechanism of color tuning in the rhodopsin family of proteins will be discussed by comparing the optical properties of the light-driven proton pump bacteriorhodopsin (bR) and the light detector sensory rhodopsin II (sRII). Despite a high structural similarity, the maximal absorption of the protein's retinal chromophores is blueshifted from 568 nm in bR to 497 nm in sRII. The molecular mechanism of this shift is still a matter of debate, and its clarification sheds light onto the general mechanisms of color tuning in retinal proteins like the visual receptors. The lecture will summarize recent calculations that employ a combined quantum mechanical/molecular mechanical (QM/MM) technique, using a DFT- based method for ground state properties and the semiempirical OM2/MRCI method and ab initio SORCI method for excited state calculations. The high efficiency of the methodology allows one to study a wide variety of aspects including dynamical effects, reproducing successfully absorption shift as well as various mutation experiments and vibrational properties.

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