Thymidine kinase mutants and fusion proteins having thymidine kinase and guanylate kinase activities
The present invention provides isolated nucleic acid molecules encoding a Herpesviridae thymidine kinase enzyme comprising one or more mutations, at least one of the mutations encoding an amino acid substitution located toward the N-terminus from a DRH nucleoside binding site which increases a biological activity of the thymidine kinase, as compared to unmutated thymidine kinase. Such mutations include amino acid substitutions within a Q substrate binding domain which increases a biological activity of the thymidine kinase, as compared to unmutated thymidine kinase. Within a further aspect, fusion proteins are provided which have both guanylate kinase and thymidine kinase biological properties. Also provided are vectors suitable for expressing such DNA molecules, as well as methods for utilizing such vectors.
1. A fusion protein comprising a guanylate kinase moiety comprising SEQ ID NO:49 and a thymidine kinase moiety, wherein said fusion protein possesses a biological activity of guanylate kinase and a biological activity of thymidine kinase, wherein said thymidine kinase moiety is either a Herpesviridae thymidine kinase of SEQ ID NO:134 or a mutant Herpesviridae thymidine kinase of SEQ ID NO:134 with an amino acid substitution at one or more of positions 159, 160, 161, 168, and 169 that possesses an increased biological activity, when to the Herpesviridae thymidine kinase of SEQ ID NO:134.
2. The isolated fusion protein according to claim 1 , wherein at least one of said guanylate kinase moiety and said thymidine kinase moiety is truncated.
3. The isolated fusion protein according to claim 1 , wherein said amino acid substitution is at positions 160,161 and 168, and wherein said amino acid substitution at position 160 is isoleucine to phenylalanine, said amino acid substitution at position 161 is phenylalanine to alanine, and said amino acid substitution at position 168 is alanine to phenylalanine.
4. The isolated fusion protein according to claim 1 , wherein said amino acid substitution is at positions 159, 160, 161 and 168, and wherein said amino acid substitution at position 159 is leucine to isoleucine, said amino acid substitution at position 160 is isoleucine to leucine, said amino acid substitution at position 161 is phenylalanine to leucine, and said amino acid substitution at position 168 is alanine to tyrosine.
5. The isolated fusion protein according to claim 1 , wherein said amino acid substitution is at positions 160, 161, 168 and 169, and wherein said amino acid substitution at position 160 is isoleucine to phenylalanine, said amino acid substitution at position 161 is phenylalanine to alanine, said amino acid substitution at position 168 is alanine to tyrosine, and said amino acid substitution at position 169 is leucine to tyrosine.
6. The isolated fusion protein according to claim 1 , wherein said amino acid substitution is at positions 160, 161, 168 and 169, and wherein said amino acid substitution at position 160 is isoleucine to phenylalanine, said amino acid substitution at position 161 is phenylalanine to valine, said amino acid substitution at position 168 is alanine to valine, and said amino acid substitution at position 169 is leucine to methionine.
7. The isolated fusion protein according to claim 1 , wherein said amino acid substitution is at positions 159, 160, 161, 168 and 169, and wherein said amino acid substitution at position 159 is leucine to isoleucine, said amino acid substitution at position 160 is isoleucine to phenylalanine, said amino acid substitution at position 161 is phenylalanine to valine, said amino acid substitution at position 168 is alanine to phenylalanine, and said amino acid substitution at position 169 is leucine to tyrosine.