Large proteins, native structure

The ROA spectra of native and prehbrillar amyloidogenic human lysozyme are displayed in Figure 7, together with a MOLSCRIPT diagram of the native structure. The ROA spectrum of the native protein is very similar to that of hen lysozyme (Fig. 5). However, large changes have occurred in the ROA spectrum of the prehbrillar intermediate. In particular, the positive 1340 cm-1 ROA band assigned to hydrated... 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

How do proteins fold into their native structures To study the mechanism of protein folding is to seek an answer to this question. The astronomically large number of possible conformations suggests that proteins use some sort of directed mechanisms to fold. Under evolutionary pressure, these mechanisms have been refined such that proteins can fold reasonably quickly to well-defined functionally useful structures. We will review briefly the history of protein folding studies and discuss the theoretical studies in more detail. We will concentrate on recent developments and give a brief perspective of the future. 

The native structure of large proteins is disrupted in several discrete stages in each of which discrete amounts of energy are absorbed. Each of these steps corresponds to the all-or-none breakdown of definite structural blocks of the protein molecule. Therefore, the large protein structure is not a monolith but appears to be composed of discrete, more or less independent, cooperative blocks, i.e., domains (Wetlaufer, 1973 Janin and Wodak, 1983 Privalov, 1982 see also Privalov et al., 1981 Privalov and Medved , 1982 Potekhin and Privalov, 1982 Novokhatny et al., 1984). 

The Gibbs energy difference of the denatured and native states corresponds to the work required for the transition of a system from the native to the denatured state, i.e., the work of disruption of the native cooperative structure. Therefore, this quantity is usually considered as a measure of the stability of the cooperative structure, i.e., the stability of a small globular protein or cooperative domain. As for the large proteins, their stability cannot be expressed by a single value, but only by a set of values specifying the stability for each domain within these molecules and the interaction between the domains. 

Because of the strict stereochemical requirements, it is not easy to find optimal sites for the introduction of disulfide bonds into proteins. Introduction of disulfide bonds into T4 lysozyme has been engineered by theoretical calculations and computer modeling.4 7 The results obtained from the mutant lysozymes illustrate several points relevant to the use of disulfide bonds for improving protein stability.6 (i) Introduction of the cysteine(s) should minimize the disruption or loss of interactions that stabilize the native structure, (ii) The size of the loop formed by the crosslink should be as large as possible, (iii) The strain energy introduced by the disulfide bond should be kept as low as possible. For this purpose, a location within the flexible part of the molecule is desirable. 

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