Heat stability of the lysozyme-substrate complex

A strategy for selecting the pH of protein solutions to enhance crystallization

The pH of a solution is an important parameter in crystallization that needs to be controlled in order to ensure success. The actual pH of the crystallization droplet is determined by the combined contribution of the buffers in the screening and protein solutions, although the contribution of the latter to the pH is often ignored. In this study, the effects of the buffer and protein solution pH values on the results of screening are systematically investigated. It was found that these parameters significantly affected the results and thus the following strategy for the selection of appropriate pH values is proposed: (i) when screening with only one protein solution, the pH should be as low, as high or as divergent from the pI as possible for a basic, acidic or neutral protein, respectively, within its stable pH range; (ii) when screening with two protein solutions, the pH values should be well separated from one another; and (iii) when multiple pH values are utilized, an even distribution of pH values is the best approach to increase the success rate of crystallization.

Dynamic behavior of oligomeric inorganic pyrophosphatase explored by quasielastic neutron scattering

The purpose of this investigation is to determine whether a large oligomeric protein, inorganic pyrophosphatase (IPPase) from Thermococcus thioreducens with quaternary structural complexity, would have distinguishable dynamic characteristics compared to those of the small simple monomeric model protein, lysozyme. In this study, the β-relaxational dynamics of the two proteins, IPPase and lysozyme, are compared in the 10 ps to 0.5 ns time interval using quasi-elastic neutron scattering (QENS). Both of the protein dynamics show a characteristic logarithmic-like decay in the intermediate scattering function (ISF) of the hydrogen atoms. Distinguishable dynamical behavior found between two proteins reveals local flexibility and conformational substates unique to oligomeric structures. Moreover, the temperature dependence of the mean square displacement (MSD) of the hydrogen atoms in protein molecules, which is a traditional way to determine the "softness" of the protein molecule, is measured and shows no difference for the two proteins.

An intramolecular cross-linkage of lysozyme. Formation of cross-links between lysine-1 and histidine-15 with bis(bromoacetamide) derivatives by a two-stage reaction procedure and properties of the resulting derivatives

Hen egg white lysozyme was treated at pH 5.5 with four bifunctional reagents, bis(bromoacetamide) derivatives [BrCH2CONH(CH2)nNHCOCH2Br, 1-n, n = 0, 2, 4, and 6], to alkylate His-15 monofunctionally. The excess bifunctional reagent was then removed, and the pH was raised to 9.0 to allow the other end of the reagent molecule to react. The shortest reagent (1-0) gave no intramolecularly cross-linked lysozyme derivative but only histidine-15-modified lysozyme monomer and intermolecularly cross-linked lysozyme dimer. However, the reagents with longer arms (1-2, 1-4, and 1-6) gave lysozyme derivatives cross-linked intramolecularly between the nitrogen at epsilon 2 of His-15 and the epsilon-amino group of Lys-1 without formation of any other intramolecularly cross-linked lysozyme derivative. These results are consistent with our previous proposal that lysozyme has a small hydrophobic pocket that binds small molecules in the direction from His-15 to Lys-1 [Yamada, H., Uozumi, F., Ishikawa, A., & Imoto, T. (1984) J. Biochem. (Tokyo) 95, 503-510]. The thermal stabilities of three cross-linked lysozymes thus obtained were investigated in 0.1 M acetate buffer containing 3 M guanidine hydrochloride at pH 5.5. All derivatives were stabilized but to different degrees. The derivative cross-linked with 1-4 was most stabilized (2.3 kcal/mol), but the derivatives cross-linked with the reagents both shorter (1-2) and longer (1-6) than 1-4 were less stabilized (both 1.6 kcal/mol).(ABSTRACT TRUNCATED AT 250 WORDS)