Methods and means for controlling the stability of proteins

A method to enhance the thermal stability of an enzyme, without destroying the catalytic activity of said enzyme which is selected from the group consisting of superoxide dismutase and glyceraldehyde phosphate dehydrogenase, which method comprises

• 1) replacing in superoxide dismutase at least one lysine residue in the primary structure of said enzyme with an arginine residue,
• wherein said lysine residue has been identified as not associated with the catalytic activity of the enzyme;
• wherein said lysine residue has been identified as located at a site that can sterically accommodate the substitution of an arginine residue;
• wherein said lysine residue has been identified as participating in electrostatic interactions at an interface between subunits or domains;
• and
• wherein said lysine residue has been identified as at a site of low accessible surface area;
• or
• 2) replacing in glyceraldehyde phosphate dehydrogenase at least one glycine residue with a lysine or arginine residue;
• wherein said glycine residue has been identified as not associated with the catalystic activity of said enzyme;
• wherein said glycine residue occurs within an interface between domains or subunits;
• and
• wherein said glycine residue is located at a site of high accessible surface area.

DNA that encodes a modified superoxide dismutase enzyme the modified enzyme having enhanced stability to chemical modification as compared to the native enzyme, without destroying the catalytic activity of said native enzyme, or an expression system for said DNA operable in a recombinant host cell, which modification comprises replacing at least one codon in the DNA which encodes a lysine residue in the primary structure of said enzyme with a codon which encodes an arginine residue,

• wherein said lysine residue has been identified as not associated with the catalytic activity of said enzyme;
• wherein said lysine residue has been identified as located at a site that can sterically accommodate the substitution of an arginine residue;
• wherein said lysine residue occurs within an interface between domains or subunits;
• and
• whereins aid lysine residue is located at a site of high accessible surface area.

A recombinant or synthetic DNA that encodes a modified enzyme selected from the group consisting of a modified superoxide dismutase and a modified glyceraldehyde phosphate dehydrogenase, the modified enzyme having enhanced thermal stability as compared to the native enzyme, without destroying the catalystic activity of said native enzyme, recombinant or synthetic DNA that encodes a modified enzyme, which modification comprises

• 1) replacing in superoxide dismutase at least one codon in the DNA which encodes a lysine residue in the primary structure of said enzyme with a codon which encodes an arginine residue,
• wherein said lysine residue has been identified as not associated with the catalytic activity of the enzyme;
• wherein said lysine residue has been identified as located at a site that can sterically accommodate the substitution of an arginine residue;
• wherein said lysine residue has been identified as participating in electrostatic interactions at an interface between subunits or domains;
• and
• wherein said lysine residue has been identified as at a site of low accessible surface area;
• or
• 2) replacing in glyceraldehyde phosphate dehydrogenase at least one codon which encodes a glycine residue with a codon which encodes a lysine or arginine residue;
• wherein said glycine residue has been identified as not associated with a catalytic activity of said enzyme;
• wherein said glycine residue occurs within an interface between domains or subunits;
• and
• wherein said glycine residue is located at a site of high accessible surface area.