| Popis: |
The Ca2+-ATPase from sarcoplasmic reticulum (SR) is exceedingly well characterized in terms of kinetics, ligand binding and amino acid sequence. For example, particular events in the reaction cycle have been assigned to specific amino acid residues by sitedirected mutagenesis and characterization of ligand binding. Various spectroscopies have documented conformational changes and measured distances between labelled amino acids. Typical of most membrane proteins, however, structural information has lagged far behind these functional studies. This is not for lack of effort as three different crystal forms have been studied by electron microscopy (11–13), oriented pellets have been studied by x-ray diffraction (2), and countless, unreported crystallization trials have failed to produce crystals suitable for x-ray crystallographic analysis. However, we are currently studying two crystal forms by cryoelectron microscopy and report here on results pertaining both to the conformational state of molecules within each crystal lattice and to their physical structures. |
