Lysozyme folding processes

However, such conclusions may not hold in general. This is evident in the second example (Table 17.2 b), where a segment of the first a helix in hen egg white lysozyme is examined. This helical segment has been shown also to be formed early in the folding process by similar NMR experiments [40]. A search for related peptides uncovers fifteen peptides of moderate similarity, of which only one adopts a fully helical fold and three are partially helical in their respective protein struetures. In... 

Shioi S, Imoto T, Ueda T (2004). Analysis of the early stage of the folding process of reduced lysozyme using all lysozyme variants containing a pair of cysteines. Biochem. 43 5488-5493. 

A. Matagne, S. E. Radford, and C. M. Dobson, East and slow tracks in lysozyme folding Insight into the role of domains in the folding process. J. Mol. Biol. 267, 1068-1074 (1997). 

Most of the main concepts regarding the mechanisms of protein folding accepted today originated from both theoretical conformational computations and the determination of structures at atomic resolution. The amount of experimental data is still insufficient to allow a high degree of generalization. The number of known proteins for which a detailed and complete study of the folding process is available, remains indeed very small. Well documented systems such as ribonuclease, staphylococcal nuclease, BPTI, lysozyme, serine proteases, and few other proteins are used frequently as examples in the discussion that follows. 

The particle has a head, within which the viral DNA is folded, and a long, fairly complex tail, at the end of which is a series of tail fibers. During the attachment process, the vims particles first attach to the cells by means of the tail fibers. These tail fibers then contract, and the core of the tail makes contact with the cell envelope of the bacterium. The action of a lysozyme-like enzyme results in the formation of a small hole. The tail sheath contracts and the DNA of the vims passes into the cell through a hole in the tip of the tail, the majority of the coat protein remaining outside. The DNA of T4 has a total length of about 50 /xm, whereas the dimensions of the head of the T4 particle are 0.095 Am by 0.065 fim. This means that the DNA must be highly folded and packed very tightly within the head. 

Additional evidence of difference in the refolding process is that the time taken for reoxidation of a-lactalbumin is longer than 25 hr, whereas that for lysozyme is only 90 min (Tamburro et al., 1972). Iyer and Klee (1973) found differences in the rates of S-S bond reduction in these proteins. Reduced a-lactalbumin retained hydrodynamic and optical properties characteristic of folded globular proteins, although its conformation was clearly distinguishable from that of the native protein. 

The SEDS process is also scalable, as recently demonstrated by its 10-fold (in terms of flow rates) scale-up of lysozyme precipitation from aqueous solutions (104). Experiments were conducted at the exact same conditions of temperature (55°C), pressure (15 MPa), and protein concentration [5% (w/v) in water] at the laboratory and pilot-plant scale. The pilot-plant-scale flow rates were 180 g/min for CO2 and 720 mL/h and 36 mL/h for ethanol and lysozyme, respectively. Similar particle morphology and activity (95% of original) were obtained under both conditions. Although Thiering et al. (119) legitimately list the possible hurdles to the scale-up of SCF-based processes, this successful scale-up indicates their potential for the industrial scale micronization of proteins. 

An important question regarding peptides and proteins is concerned with the equilibria among several conformational states. It has been suggested that enzyme function may be linked to the occurrence of particular conformations in solution.24 377 A mechanism recently proposed for the hydrolysis of oligosa-charides by the enzyme lysozyme, for example, is based on the observation of specific substrate and enzyme sidechain conformations in a molecular dynamics simulation of a lysozyme-substrate complex.378 Also, local conformational equilibria and the barriers between conformations are important in determining the rates and mechanisms of folding and rebinding processes. 

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