Three-dimensional strutural study of the sarcoplasmic reticulum clcium ATPase under various physiological conditions.

点击翻译按钮获取中文摘要

The purpose of this research is to reveal the three-dimensional structure of calcium ATPase under various physiological conditions and thereby elucidate the structural aspects of active transport. At the first stage, 3D structure of calcium ATPase without ATP was solved at 14 A resolution by frozen-hydrated electron microscope of the tubular crystals. In our paper published in Nature, we described that the transmembrane structure is unique, consisting of three distinct segments ; it was also possible to correlate the density map to the secondary structure predicted from the amino acid sequence. At the second stage, three-simensional structure of this enzyme was solved with chromium ATP, a non-hydrolysable analog of ATP.Detailed comparison of two structures revealed that groove predicted to be the ATP binding pocket was filled and one of the surrounding domains has moved towards the groove as if putting a lid to the binding pocket. Distinct structural changes were also found with transmembrance segments and luminal domains, demonstrating that the effect of ATP binding is transmitted across the membrane. Furthermore, we have obtained views along the lipid bilayr of 3D microcrystals of this enzyme grown under a high concentrationof calcium. Though the number of images was limited, the resolution was better than 10 A.On the other hand, a suit of programs has been developed for correcting distortion in helical lattice. It has now become usable and been applied to images of tubular crystals of calcium ATPase. The Fourier tranforms after the sistortion correction appeared much better. Thus, it is very likely that we can resolve individual alpha-helices in this enzyme in a very near future.