Protein crystals properties

Hagler A T and S Lifson 1974. Energy Functions for Peptides and Proteins. II. The Amide Hydrogen Bond and Calculation of Amide Crystal Properties. Journal of the American Chemical Society 96 5327-5335. 

In NMR the magnetic-spin properties of atomic nuclei within a molecule are used to obtain a list of distance constraints between those atoms in the molecule, from which a three-dimensional structure of the protein molecule can be obtained. The method does not require protein crystals and can be used on protein molecules in concentrated solutions. It is, however, restricted in its use to small protein molecules. 

Freely suspended liquid droplets are characterized by their shape determined by surface tension leading to ideally spherical shape and smooth surface at the subnanometer scale. These properties suggest liquid droplets as optical resonators with extremely high quality factors, limited by material absorption. Liquid microdroplets have found a wide range of applications for cavity-enhanced spectroscopy and in analytical chemistry, where small volumes and a container-free environment is required for example for protein crystallization investigations. This chapter reviews the basic physics and technical implementations of light-matter interactions in liquid-droplet optical cavities. 

New glycolipids have to be synthesized to get further insights into liquid crystal properties (mainly lyotropic liquid crystals), surfactant properties (useful in the extraction of membrane proteins), and factors that govern vesicle formation, stability and tightness. New techniques have to be perfected in order to allow to make precise measurements of thermodynamic and kinetic parameters of binding in 3D-systems and to refine those already avalaible with 2D-arrays. Furthermore, molecular mechanics calculations should also be improved to afford a better modeling of the conformations of carbohydrates at interfaces, in relation with physical measurements such as NMR. 

The molecular dynamics unit provides a good example with which to outline the basic approach. One of the most powerful applications of modem computational methods arises from their usefulness in visualizing dynamic molecular processes. Small molecules, solutions, and, more importantly, macromolecules are not static entities. A protein crystal structure or a model of a DNA helix actually provides relatively little information and insight into function as function is an intrinsically dynamic property. In this unit students are led through the basics of a molecular dynamics calculation, the implementation of methods integrating Newton s equations, the visualization of atomic motion controlled by potential energy functions or molecular force fields and onto the modeling and visualization of more complex systems. 

In protein crystals, due to the large size of the molecule, the empty space can have cross sections of 10-15 A or greater. The empty space between the protein molecules is occupied by mother liquor. This property of protein crystals, shared by nucleic acids and viruses, is otherwise unique among the crystal structures. In fact, the values of the packing coefficient of protein crystals range from 0.7 to 0.2, but the solvent molecules occupy the empty space so that the total packing coefficient is close to 1 [37]. Nevertheless, a detailed theoretical study has been carried out to examine the models of DNA-DNA molecular interactions on the basis of hard-sphere contact criteria. The hard-sphere computations are insufficient for qualitative interpretation of the packing of DNA helices in the solid state, but... 

While the most obvious advantage of microfluidics is the enormous reduction in sample consumption, the growth of protein crystals can also be fundamentally improved by taking advantage of the physical properties of fluid flow at the mi-... 

As discussed below, crystallization of the enzyme is also an effeetive method for removing contaminating and denatured proteins. Crystallization has the potential to produce a preparation not only of high purity but also of extreme reproducibility in both composition and enzyme aetivity. An important property of crystallization is its inherent eapability to seleet for protein molecules that possess the same three dimensional strueture. This is in eontrast to other purification steps which are likely to induee some degree of denaturation. 

An important feature of protein crystal growth experiments is the need to carry out crystallization trials with very small quantities of scarce and expensive materials. When experiments are carried out in such small volumes (typically, 5—100 ju.1), it becomes difficult to define and control solution properties. The situation becomes particularly complicated when vapor diffusion or other nonequilibrium approaches to crystal growth are used, as these produce different and changing conditions throughout the small volumes involved. 

Usha and Wittebort (1989) studied the NMR of crystalline cram-bin. At 140 K the protein hydrate is stationary, with t = 1 msec. Above 200 K changes in the signal with temperature are consistent with a glass transition or melting of the hydration water. This broad transition parallels closely the changes with temperature found for the heat capacity, Mossbauer spectroscopic, and other properties of hydrated protein crystals. At room temperature no more than 12 water molecules are orien-tationally ordered. The average rotational correlation time of the hydration water is about 40 times longer than that for bulk water. 

Hagler, A. T. and Lifson, S. (1974). Energy functions for peptides and proteins. II. Amide hydrogen bond and calculation of amide crystal properties. J. Am. Chem. Soc., 96, 5327-35. [153, 167]... 

Wiener MC. The development of membrane protein crystallization screens based upon detergent solution properties. Biophys. J. 2002 82 29a. 

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