Lysozyme thermal, mutants

In contrast, in phage T4 lysozyme a thermolabile mutant was found in which one single amino acid was exchanged Thr- Ile 157, and the thermal melting point dropped from 42°C for the wild-type enzyme to 31 °C for the mutant. Systematic exchange of the amino acid in position 157 by site-directed mutagenesis led to the... 

Table FV. Side-chain thermal factors in wild-type and a seven-methionine mutant lysozyme...

Singla et al. [19] examined the adsorption kinetics of wild type and two synthetic stability mutants of T4 phage lysozyme at silanized silica surfaces. Substitution of the isoleucine at amino acid position three with cysteine (13 C) and tryptophan (13W) rendered such mutants with a higher and lower thermal stability, respectively. It was found that the I3W mutant, characterized by a lower structural stability, would more readily undergo a stmctural change at the interface. Moreover, such a mutant showed more resistance to elution by DTAB than either the wild type or 13 C mutant, simply by forming a more tightly bound conformation (adsorbed state) with the adsorbent. 

In addition, it was also shown [44] that DTAB-mediated elutabihty was positively eorrelated with the thermal struetural stability of the above-mentioned types of lysozyme. In other words, the resistance to elutabihty eorrelates with 02/0 ratio, the nonremovable fractional surface eoverage divided by the removable fractional siuface coverage, which, in turn, correlates with the extent of surface-indueed unfolding (i.e., in our case). As far as the surface-induced unfolding on the hydrophihe surface is eoneemed, the least thermally stable mutant (i.e., BW) exhibited the highest value of f/gju, whereas the wild type exhibited the lowest value of Apparently, there is a switch in order between the wild type and the most stable form, which is DC. It was shown [19] that the speetral differenees between the wild type and I3C were relatively small. Nevertheless, the differenee in kinetie behavior between the wild type and I3C is small, compared with that of I3W. 

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