GENETIC FUSION OF SUBUNITS OF A DIMERIC PROTEIN SUBSTANTIALLY ENHANCES ITS STABILITY AND RATE OF FOLDING

The gene V protein of bacteriophage f1 is a single-stranded DNA and RN A-binding protein composed of two identical subunits. We have construc ted single-chain variants of the protein using short peptide linkers o f five or six amino acids to connect the carboxyl terminus of one mono mer to the amino terminus of the second monomer. The resulting subunit -fusion gene V proteins were found to bind single-stranded DNA nearly as tightly as the wild-type protein. Denaturation measurements show th at the subunit-fusion gene V proteins are 5 kcal/mol (1 kcal = 4.18 kJ ) more stable than the wild-type protein at a protein concentration of 10 muM. The rate of unfolding of the protein is essentially unaffecte d by the fusion of monomeric subunits, whereas the rate of folding is greatly enhanced. Our results suggest a simple way of obtaining a subs tantial thermodynamic stabilization for some oligomeric proteins.