Growth kinetics and diffraction properties of STMV crystals
- PDF / 2,700,183 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 198 Views
Growth kinetics and diffraction properties of STMV crystals
Yu. G. Kuznetsov, A. J. Malkin and A. McPherson University of California, Irvine Department of Molecular Biology and Biochemistry Irvine, CA 92697-3900 ABSTRACT Two crystal forms, orthorhombic and cubic, of satellite tobacco mosaic virus have been investigated. Atomic force microscopy showed that the orthorhombic crystals were characterized by a high density of point defects, while the cubic crystals were practically defectfree. Nonetheless, orthorhombic crystals diffract to a high resolution of 1.8 Å while the cubic crystals diffract to only about 4 to 6 Å resolution. Differences in the properties of viruses incorporated into the two crystal structures were demonstrated by growth kinetics studies. It appears that physical and chemical treatments applied to protein and virus solutions during their extraction and purification introduce a variety of specific structural changes and that these alterations may then affect the diffraction properties of resultant macromolecular crystals. INTRODUCTION The influence of crystal defects, such as point and linear defects, stacking faults, and grain boundaries present in X-ray diffraction data from inorganic crystals have been thoroughly studied. Results from these studies have been applied to macromolecular crystals to explain their marginal diffraction properties, but in most cases the arguments are not convincing. The sizes of the crystals and the estimated sizes of their blocks are, in general, large enough to yield X-ray data of high resolution. Furthermore, from AFM studies it is known that many macromolecular crystals are dislocation-free or have no more than a few dislocations. To improve macromolecular crystal quality, extensive purification of protein solutions (filtration, recrystallization), application of more precise growth techniques such as temperature control, and even microgravity conditions have been used [1-3]. Such efforts have improved matters in some cases, but not for all macromolecular crystals studied. In many cases there were no improvements at all. Polypeptide chains making up a protein are twisted or folded to form a macromolecule with a specific three-dimensional conformation. Globular proteins composed of two or more polypeptide chains have four levels of organization referred to as primary, secondary, tertiary and quaternary structure. All levels use the same kind of bonds, which include hydrogen bonds, ionic, and covalent bonds, and hydrophobic interactions. Biological function, which is determined by the three-dimensional structure, can be altered either by replacement of an amino acid in the polypeptide chain sequence with another (mutation) or by altering the bonding pattern. Changes in shape and biological activity are also frequently observed when a protein is heated or treated with any number of chemicals. The same kinds of interactions that are used to construct protein structure are also used between protein molecules to build crystal structure. Generally speaking, any physical
Data Loading...
