Lysozyme enzyme

Figure 6.6 Schematic diagram of the structure of the enzyme lysozyme which folds into two domains. One domain is essentially a-helical whereas the second domain comprises a three stranded antiparallel p sheet and two a helices. There are three disulfide bonds (green), two in the a-helical domain and one in the second domain.

At best, van der Waals interactions are weak and individually contribute 0.4 to 4.0 kj/mol of stabilization energy. ITowever, the sum of many such interactions within a macromolecule or between macromolecules can be substantial. For example, model studies of heats of sublimation show that each methylene group in a crystalline hydrocarbon accounts for 8 k[, and each C—IT group in a benzene crystal contributes 7 k[ of van der Waals energy per mole. Calculations indicate that the attractive van der Waals energy between the enzyme lysozyme and a sugar substrate that it binds is about 60 k[/mol. 

Just as individual amino acids have isoelectric points, proteins have an overall p/ because of the acidic or basic amino acids they may contain. The enzyme lysozyme, for instance, has a preponderance of basic amino acids and thus has a high isoelectric point (p/= 11.0). Pepsin, however, has a preponderance of acidic amino acids and a low- isoelectric point pi 1.0). Not surprisingly, the solubilities and properties of proteins with different pi s are strongly affected by the pH of the medium. Solubility- is usually lowest at the isoelectric point, where the protein has no net charge, and is higher both above and below the pi, where the protein is charged. 

Mar f body secretions contain substances that exert abacteriddal action, for example the enzyme lysozyme which is found in tears, nasal secretions and saliva hydrochloric acid in the stomach which results in a low pH and basic polypeptides such as spermine which are found in semen. 

Disruption of microbial cells is rendered difficult due to the presence of the microbial cell wall. Despite this, a number of very efficient systems exist that are capable of disrupting large quantities of microbial biomass (Table 6.1). Disruption techniques, such as sonication or treatment with the enzyme lysozyme, are usually confined to laboratory-scale operations, due either to equipment limitations or on economic grounds. 

Figure 2.10 Secondary and tertiary structure of the enzyme lysozyme, PDB 2C80. Visualized using Cambridge Soft Chem3D Ultra 10.0 with notations in ChemDraw Ultra 10.0. ChemDraw Ultra, version 10.0. (Printed with permission of CambridgeSoft...

One ionic bond that often helps establish tertiary structure is a disulfide bond between two cysteine side chain groups—for instance, in the enzyme lysozyme as shown in Figure 2.10. Lysozyme is not a metalloprotein, such as will be studied in this text, but it is a small enzyme and is illustrative of some secondary and tertiary structures found in the more complex molecules described in the following chapters. Lysozyme protects biological species from... 

The maximum rate is directly related to the rate at which the enzyme processes or permits conversion of the reactant molecule(s). The number of moles of reactants processed per mole of enzyme per second is called the turnover number. Turnover numbers vary widely. Some are high, such as for the scavenging of harmful free radicals by catalase, with a turnover number of about 40 million. Others are small, such as the hydrolysis of bacterial cell walls by the enzyme lysozyme, with a turnover number of about one half. 

Base-pairs in the gene, needed to code for the enzyme lysozyme (129 amino acids) found in egg white. 

In this exercise you will examine the interactions between the enzyme lysozyme (Chapter 4) and the Fab portion of the anti-lysozyme antibody. Use the PDB identifier 1FDL to explore the structure of the IgGl Fab fragment-lysozyme complex (antibody-antigen complex). View the structure using Protein Explorer, and also use the information in the PDBsum summary of the structure to answer the following questions. 

The chymotiypsin reaction is one example of acyl group transfer (see Fig. 6-21). Glycosyl group transfers involve nucleophilic substitution at C-l of a sugar ring, which is the central atom of an acetal. In principle, the substitution could proceed by an SnI or Sn2 path, as described for the enzyme lysozyme (see Fig. 6-25). 

The first protein structure to be learned was that of myoglobin, which was established by Kendrew et al. in I960.391-393 That of the enzyme lysozyme was deduced by Blake et al. in 1965.394 Since then, new structures have appeared at an accelerating rate so that today we know the detailed architecture of over 6000 different proteins395 with about 300 distinctly different folding patterns 396 New structures are being determined at the rate of about one per day. X-ray diffraction has also been very important to the study of naturally or artifically oriented fibrous proteins397 and provided the first experimental indications of the P structure of proteins. 

Figure 25-29 shows an unusually well-resolved 13C nmr spectrum of the enzyme lysozyme (Table 25-3 and Figure 25-15) taken with proton decoupling. The closely spaced peaks on the left side of the spectrum are of the carbonyl groups. The peaks in the center are of unsaturated and aromatic carbons, while those on the right are of the aliphatic amino acid carbons. The five sharp resonances marked at about 110 ppm with arise from tryptophan carbons marked with in 22 ... 

The structure of the complex formed between the enzyme lysozyme and its substrate. The crevice that forms the site for substrate binding (the active site) runs horizontally across the enzyme molecule. The individual hexose sugars of the hexasaccharide substrate are shown in a darker color and labeled A-F. (Coordinates courtesy of D. C. Philips, Oxford, England.) (Illustration copyright by Irving Geis. Reprinted by permission.)... 

The complexity of this problem is illustrated in Fig. 3.3, which shows the effects of varying just two parameters, the concentrations of protein (in this case, the enzyme lysozyme) and precipitant (NaCI). Notice the effect of slight changes in concentration of either protein or precipitant on the rate of crystallization, as well as the size and quality of the resulting crystals. 

The antibacterial enzyme lysozyme is also found in nasal secretions. Lysozyme is produced by the epithelium and mucus glands where it can attack the cell walls of susceptible microorganisms, its action being optimal at the slightly acidic microclimate pH. The pH of nasal mucus varies with age, sleep, rest, emotion, infection, and diet. When it is cold, or during rhinitis or sinusitis, the pH tends to be alkaline, which deactivates the lysozyme in mucus and therefore increases the risk of microbial infection. Under normal conditions, the nasal secretions, as indicated earlier, have a pH of 5.5 to 6.5, which is the optimum pH for the activity of lysozyme. 

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