Effect of foreign N-terminal residues on the conformational stability of human lysozyme.
To minutely understand the effect of foreign N-terminal residues on the conformational stability of human lysozyme, five mutant proteins were constructed: two had Met or Ala in place of the N-terminal Lys residue (K1M and K1A, respectively), and others had one additional residue, Met, Gly or Pro, to the N-terminal Lys residue (Met(-1), Gly(-1) and Pro(-1), respectively). The thermodynamic parameters for denaturation of these mutant proteins were examined by differential scanning calorimetry and were compared with that of the wild-type protein. Three mutants with the extra residue were significantly destabilized: the changes in unfolding Gibbs energy (DeltaDeltaG) were -9.1 to -12.2 kJ.mol-1. However, the stability of two single substitutions at the N-terminal slightly decreased; the DeltaDeltaG values were only -0.5 to -2.5 kJ.mol-1. The results indicate that human lysozyme is destabilized by an expanded N-terminal residue. The crystal structural analyses of K1M, K1A and Gly(-1) revealed that the introduction of a residue at the N-terminal of human lysozyme caused the destruction of hydrogen bond networks with ordered water molecules, resulting in the destabilization of the protein.
Takano
K
K
Institute for Protein Research, Osaka University, Yamadaoka, Suita, Osaka, Japan.
Tsuchimori
K
K
Yamagata
Y
Y
Yutani
K
K
D000409:Alanine / Q000737:chemistry; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008715:Methionine / Q000737:chemistry; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry*; D009154:Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013696:Temperature; D013816:Thermodynamics
D008715:Methionine; D009113:Muramidase; D000409:Alanine