[The effect of point amino acid substitutions on T4 phage lysozyme stability. II. Transition of a protein molecule to the "molten globule" state with replacements Asp10---His, Asn101---Asp, Arg148---Ser].

The amino acid replacements (Asp10-->His, Asn101-->Asp, Arg148-->Ser) in the T4 phage lysozyme were obtained by site directed mutagenesis and the plasmid for mutant protein expression was constructed. At acid pH (pH 2.7) the mutant is in the conformational state with properties of the molten globule (Ptitsyn, 1992): 1) the mutant protein molecule is essentially compact, 2) its circular dichroism (CD) spectrum in the near ultra violet (UV) region is drastically reduced in intensity as compared with the wild type protein spectrum, 3) the CD spectrum in the far UV region indicates the presence of a pronounced secondary structure in the mutant, 4) unlike the wild type protein, the mutant protein can bind the hydrophobic fluorescent probe ANS.