X-Ray diffraction experiments for drug target protein of human casein kinase II

Casein kinase II (CKII) exhibits broad phosphorylation reaction on various important regulatory proteins such as survival factors in eukaryotic cells. Since the relationship of CKII over-expression to carcinogenesis and cancer metastasis has been reported, CKII is considered to be one of the drug target proteins. Here, we aimed to obtain the structural information with location of hydration water molecules, and to elucidate the catalytic reaction of CKII for development of effective inhibitors

Cl(-) concentration dependence of photovoltage generation by halorhodopsin from Halobacterium salinarum.

The photovoltage generation by halorhodopsin from Halobacterium salinarum (shR) was examined by adsorbing shR-containing membranes onto a thin polymer film. The photovoltage consisted of two major components: one with a sub-millisecond range time constant and the other with a millisecond range time constant with different amplitudes, as previously reported. These components exhibited different Cl(-) concentration dependencies (0.1-9 M). We found that the time constant for the fast component was relatively independent of the Cl(-) concentration, whereas the time constant for the slow component increased sigmoidally at higher Cl(-) concentrations. The fast and the slow processes were attributed to charge (Cl(-)) movements within the protein and related to Cl(-) ejection, respectively. The laser photolysis studies of shR-membrane suspensions revealed that they corresponded to the formation and the decay of the N intermediate. The photovoltage amplitude of the slow component exhibited a distorted bell-shaped Cl(-) concentration dependence, and the Cl(-) concentration dependence of its time constant suggested a weak and highly cooperative Cl(-)-binding site(s) on the cytoplasmic side (apparent K(D) of approximately 5 M and Hill coefficient > or =5). The Cl(-) concentration dependence of the photovoltage amplitude and the time constant for the slow process suggested a competition between spontaneous relaxation and ion translocation. The time constant for the relaxation was estimated to be >100 ms

Polypentagonal ice-like water networks emerge solely in an activity-improved variant of ice-binding protein

Polypentagonal water networks were recently observed in a protein capable of binding to ice crystals, or ice-binding protein (IBP). To examine such water networks and clarify their role in ice-binding, we determined X-ray crystal structures of a 65-residue defective isoform of a Zoarcidae-derived IBP (wild type, WT) and its five single mutants (A20L, A20G, A20T, A20V, and A20I). Polypentagonal water networks composed of similar to 50 semiclathrate waters were observed solely on the strongest A20I mutant, which appeared to include a tetrahedral water cluster exhibiting a perfect position match to the (1010) first prism plane of a single ice crystal. Inclusion of another symmetrical water cluster in the poly-pentagonal network showed a perfect complementarity to the waters constructing the (2021) pyramidal ice plane. The order of ice-binding strength was A20L < A20G < WT < A20T < A20V < A20I, where the top three mutants capable of binding to the first prism and the pyramidal ice planes commonly contained a bifurcated gamma-CH3 group. These results suggest that a fine-tuning of the surface of Zoarcidae-derived IBP assisted by a side-chain group regulates the holding property of its polypentagonal water network, the function of which is to freeze the host protein to specific ice planes

Direct Observation of the Protonation States in the Mutant Green Fluorescent Protein

Neutron crystallography has been used to elucidate the protonation states for the enhanced green fluorescent protein, which has revolutionized the imaging technologies. The structure has a deprotonated hydroxyl group in the fluorescent chromophore. Also, the protonation states of His148 and Thr203, as well as the orientation of a critical water molecule in direct contact with the chromophore, could be determined. The results demonstrate that the deprotonated hydroxyl group in the chromophore and the nitrogen atom ND1 in His148 are charged negatively and positively, respectively, forming an ion pair. The position of the two deuterium atoms in the critical water molecule appears to be displaced slightly toward the acceptor oxygen atoms according to their omit maps. This displacement implies the formation of an intriguing electrostatic potential realized inside the protein. Our findings provide new insights into strategy for future protein design with developments for quantum chemical calculations

Direct Observation of the Protonation States in the Mutant Green Fluorescent Protein

Neutron crystallography has been used to elucidate the protonationstates for the enhanced green fluorescent protein, which has revolutionized imagingtechnologies. The structure has a deprotonated hydroxyl group in the fluorescentchromophore. Also, the protonation states of His148 and Thr203, as well as theorientation of a critical water molecule in direct contact with the chromophore, couldbe determined. The results demonstrate that the deprotonated hydroxyl group in thechromophore and the nitrogen atom ND1 in His148 are charged negatively andpositively, respectively, forming an ion pair. The position of the two deuterium atomsin the critical water molecule appears to be displaced slightly toward the acceptoroxygen atoms according to their omit maps. This displacement implies the formationof an intriguing electrostatic potential realized inside of the protein. Our findingsprovide new insights into future protein design strategies along with developments inquantum chemical calculations