2010 Volume 59 Issue 4 Pages 289-297
The hydrogen bond network were studied by high-resolution neutron crystallography. Two short hydrogen bonds are involved in the hydrogen bond network as well as the ordinary hydrogen bonds. A fairly large crystal of photoactive yellow protein(PYP)(2.89×0.85×0.79mm3)required for the neutron crystallography was successfully prepared and the obtained crystal diffracts X-rays and neutrons to 0.125 nm and 0.15 nm, respectively. A new refinement method with the combination of X-ray diffraction and neutron diffraction revealed the presence of 819 hydrogen atoms among total 942 hydrogen atoms. The short hydrogen bond between the chromophore and E46 was identified as the low barrier hydrogen bond, while the short hydrogen bond between the chromophore and Y42 was the short ionic hydrogen bond. The expected counter ion, R52, is revealed to be in electrically neutral. The observation leads to the proposal of the novel mechanism of charge stabilization. The role of low barrier hydrogen bond in the photoreaction of PYP is also discussed.
