膜タンパク質の構造生理学

抄録

I am personally interested in molecular mechanisms, how education and other experiences during human development influence cognitive ability and personality in the adult. For understanding brain and other biological functions from molecular level, structure analyses of membrane proteins are important and electron microscopy is a good candidate for structure analyses of membrane proteins. Radiation damage of biological material is however extremely serious. We therefore developed a helium cooled cryo–EM. Based on electron crystallography utilizing the cryo–EM, for example, we could discriminate 8 water molecules in water channel AQP4, while their densities were blurred in the higher resolution structure by X–ray crystallography. The counterintuitive notion could be attributed to the difference of surround atmosphere for structure analyses of membrane proteins. The characteristic distribution of the dielectric constants in membrane produces large dipole moment of the two short helices of water channel, whereas the dipole moment without lipid bilayer is very small. In cooperation with the electrostatic field of two short helices, the arrangement of carbonyl groups in the channel acts as binding sited in the narrow channel with highly hydrophobic surfaces and lowers the energy barrier for water molecules entering narrow water channel. The water stable positions guided by the polypeptide carbonyl and amide groups of highly conserved NPA motifs may make 3 billion water molecules pass through the channel in a second. The results strongly suggest that electron crystallography is very powerful method for understanding physiological functions of membrane proteins. The necessity of crystallization, however, makes this method less popular in structural biology. Now, many structures have been analyzed by single particle analysis. Actually, we could analyze structure of gap junction channel of invertebrate in very short period, while we could analyze no high resolution structure of it by crystallography. The good quality map at 3.3 Å resolution by cryo–EM single particle analysis enables us to make de novo chain tracing. Very effective and fast structure analysis of membrane protein may facilitate to develop a new strategy named drug rescuing.