Introduction of a disulfide bond by site-directed mutagenesis was found to enhance the stability of subtilisin BPN' (EC 184.108.40.206) under a variety of conditions. The location of the new disulfide bond was selected with the aid of a computer program, which scored various sites according to the amount of distortion that an introduced disulfide linkage would create in a 1.3-A X-ray model of native subtilisin BPN'. Of the several amino acid pairs identified by this program as suitable candidates, Thr-22 and Ser-87 were selected by using the additional requirement that the individual cysteine substitutions occur at positions that exhibit some degree of variability in related subtilisin amino acid sequences. A subtilisin variant containing cysteine residues at positions 22 and 87 was created by site-directed mutagenesis and was shown to have an activity essentially equivalent to that of the wild-type enzyme. Differential scanning calorimetry experiments demonstrated the variant protein to have a melting temperature 3.1 degrees C higher than that of the wild-type protein and 5.8 degrees C higher than that of the reduced form (-SH HS-) of the variant protein. Kinetic experiments performed under a variety of conditions, including 8 M urea, showed that the Cys-22/Cys-87 disulfide variant undergoes thermal inactivation at half the rate of that of the wild-type enzyme. The increased thermal stability of this disulfide variant is consistent with a decrease in entropy for the unfolded state relative to the unfolded state that contains no cross-link, as would be predicted from the statistical thermodynamics of polymers. Study holds ProTherm entries: 3031, 3032, 3033, 3034 Extra Details: additive : EDTA(10 mM), subtilisin BPN'; disulfide bond; protein engineering;,cysteine; statistical thermodynamics; stabilization
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:20 p.m.
|Number of data points||8|
|Proteins||Subtilisin BPN' ; Subtilisin BPN'|
|Assays/Quantities/Protocols||Experimental Assay: Tm ; Derived Quantity: dTm|
|Libraries||Mutations for sequence AQSVPYGVSQIKAPALHSQGYTGSNVKVAVIDSGIDSSHPDLKVAGGASMVPSETNPFQDNNSHGTHVAGTVAALNNSIGVLGVAPSASLYAVKVLGADGSGQYSWIINGIEWAIANNMDVINMSLGGPSGSAALKAAVDKAVASGVVVVAAAGNEGTSGSSSTVGYPGKYPSVIAVGAVDSSNQRASFSSVGPELDVMAPGVSIQSTLPGNKYGAYNGTSMASPHVAGAAALILSKHPNWTNTQVRSSLENTTTKLGDSFYYGKGLINVQAAAQ|