Thermophilic organisms produce proteins of exceptional stability. To understand
protein thermostability at the molecular level we studied a pair of cold shock
proteins, one of mesophilic and one of thermophilic origin, by systematic
mutagenesis. Although the two proteins differ in sequence at 12 positions,
two surface-exposed residues are responsible for the increase in stability
of the thermophilic protein (by 15.8 kJ mol-1 at 70 °C).
11.5 kJ mol-1 originate from a predominantly electrostatic
contribution of Arg 3 and 5.2 kJ mol-1 from hydrophobic
interactions of Leu 66 at the carboxy terminus. The mesophilic protein could
be converted to a highly thermostable form by changing the Glu residues at
positions 3 and 66 to Arg and Leu, respectively. The variation of surface
residues may thus provide a simple and powerful approach for increasing the
thermostability of a protein.
