4i38

Publication Abstract from PubMed

Trans-to-cis isomerization, the key reaction in photoactive proteins, usually cannot occur through the standard one-bond-flip mechanism. Owing to spatial constraints imposed by a protein environment, isomerization probably proceeds through a volume-conserving mechanism in which highly choreographed atomic motions are expected, the details of which have not yet been observed directly. Here we employ time-resolved X-ray crystallography to visualize structurally the isomerization of the p-coumaric acid chromophore in photoactive yellow protein with a time resolution of 100 ps and a spatial resolution of 1.6 A. The structure of the earliest intermediate (I(T)) resembles a highly strained transition state in which the torsion angle is located halfway between the trans- and cis-isomers. The reaction trajectory of I(T) bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue through E46Q mutation, which switches off the bicycle-pedal pathway.

Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography.,Jung YO, Lee JH, Kim J, Schmidt M, Moffat K, Srajer V, Ihee H Nat Chem. 2013 Mar;5(3):212-20. doi: 10.1038/nchem.1565. Epub 2013 Feb 3. PMID:23422563^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.