EFFECT OF SINGLE AMINO-ACID REPLACEMENTS ON T4 PHAGE LYSOZYME STABILITY .2. POINT MUTATIONS ASP10-]HIS, ASN101-]ASP, ARG148-]SER LEAD TO THE MOLTEN GLOBULE STATE

The aminoacid replacements (Asp10-->His, Asn101-->Asp, Arg148-->Ser) i n 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 n ear ultra violet (UV) region is drastically reduced in intensity as co mpared with the wild type protein spectrum, 3) the CD spectrum in the far UV region indicates the presente of a pronounced secondary structu re in the mutant, 4) unlike the wild type protein, the mutant protein can bind the hydrophobic fluorescent probe ANS.