Rational evolution of cytokines for higher stability, the cytokines and encoding nucleic acid molecules

1. A method for generating a cytokine having a predetermined property or activity, the method comprising:

(a) identifying, within a target cytokine or plurality thereof, target amino acids, wherein:

each target amino acid is designated an in silico-HIT (is-HIT); and

the is-HIT target amino acids are identified by identifying structurally homologous loci between the target cytokine and a reference cytokine possessing a predetermined activity, wherein:

the predetermined property or activity is resistance to proteolysis; and

identification of the structurally homologous loci between the target cytokine and the reference cytokine possessing the predetermined activity is effected by:

(i) comparing the 3-dimensional structures of the two or more proteins to identify regions of high coincidence between their backbones, said regions designated as structurally homologous regions, wherein the degree of coincidence between the 3-dimensional structures of the target cytokine and of the reference cytokine is determined by superposition and root means squared (RMS) deviation calculations using any combination of one or more of the peptide backbone atoms selected from the group consisting of: N, C, C(C═O), O and CA: and

(ii) identifying is-HIT structurally homologous loci on the target cytokine that correspond to structurally related is-HIT amino acid positions within a structurally homologous region of the reference cytokine;

(b) identifying one or more replacement amino acids, specific for each is-HIT, wherein:

each cytokine comprising a single amino acid replacement within the target cytokine is designated as a candidate LEAD protein; and

the replacement amino acids are selected using Percent Accepted Mutations (PAM) matrices;

(c) producing a population of separate sets of nucleic acid molecules, wherein:

each set encodes a different candidate LEAD protein;

all nucleic acid molecules in a set encode the same protein;

each candidate LEAD protein contains a single amino acid replacement; and

each set of nucleic acid molecules encodes a candidate LEAD protein that differs by one amino acid from the target cytokine;

(d) separately introducing each set of nucleic acid molecules into host cells and expressing the encoded candidate LEAD proteins, whereby the host cells comprise an addressable array such that each LEAD protein is expressed at a different locus in the array, and the identity of each candidate LEAD protein at each locus is known; and

(e) individually screening each set of encoded candidate LEAD proteins to identify one or more proteins that has an activity that differs from an activity an unmodified target cytokine wherein:

each such cytokine is designated a LEAD mutant protein.

2. The method of claim 1 , wherein the cytokine is selected from among interleukin-10 (IL-10), interferon beta (IFNβ), interferon alpha (IFNα), interferon gamma (IFNγ), granulocyte colony stimulating factor (G-CSF), leukemia inhibitory factor (LIF), human growth hormone (hGH), ciliary neurotrophic factor (CNTF), leptin, oncostatin M, interleukin-6 (IL-6) and interleukin-12 (IL-12), erythropoietin (EPO), granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-2 (IL-2), interleukin-3 (IL-3), interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-13 (IL-13), Flt13 ligand and stem cell factor (SCF).

3. The method of claim 1 , wherein each candidate LEAD protein is individually prepared and screened to identify LEAD mutant proteins.

4. The method of claim 1 , wherein the nucleic acid molecules comprise plasmids.

5. The method of claim 1 , wherein the host cells are eukaryotic cells or bacterial cells.

6. The method of claim 1 , wherein the nucleic acid molecules in step (c) are produced by site-specific mutagenesis.

7. The method of claim 1 , further comprising:

(f) generating a population of sets of nucleic acid molecules encoding a set of candidate super-LEAD proteins, wherein:

each candidate super-LEAD protein comprises a combination of two or more of the ingle amino acid replacements derived from two or more LEAD mutant proteins;

each set encodes a different candidate super-LEAD protein; and

all nucleic acid molecules in a set encode the same protein;

(g) introducing each set of nucleic acid molecules encoding candidate super-LEAD proteins into cells and expressing the encoded candidate super-LEAD proteins; and

(h) individually screening each set of encoded candidate super-LEAD proteins to identify one or more proteins that has activity that differs from the unmodified target cytokine and has properties that differ from the original LEAD mutant proteins, wherein each such protein is designated a super-LEAD.

8. The method of claim 7 wherein the nucleic acid molecules in step (f) are produced by a method selected from among recombination, mutagenesis, nucleic acid shuffling, additive directional mutagenesis (ADM), multi-overlapped primer extensions, oligonucleotide-mediated mutagenesis, and de novo synthesis.

9. The method of claim 1 , wherein:

the replacement amino acids identified in step (b) correspond to a restricted subset of the 19 remaining non-native amino acids; and

a restricted subset is a group of amino acids selected to confer resistance to proteolysis.

10. The method of claim 1 , wherein the nucleic acids of step (c) are produced by systematically replacing each codon that is an is-HIT, with a codon encoding an amino acid selected from among a restricted subset of the 19 remaining non-native amino acids, to produce nucleic acid molecules each differing by at least one codon and encoding candidate LEAD proteins.

11. The method of claim 7 , wherein the number of LEAD amino acid positions generated on a single nucleic acid molecule is selected from the group consisting of: two, three, four, five, six, seven, eight, nine, ten or more LEAD amino acid positions up to all of the LEAD amino acid positions.

12. The method of claim 1 , wherein the LEAD mutant protein possesses increased resistance to proteolysis compared to the unmodified target cytokine.

13. The method of claim 7 , wherein the super-LEAD possesses increased resistance to proteolysis compared to the unmodified target cytokine.

14. The method of claim 1 , wherein the target cytokine and the reference cytokine are sequence-related proteins.

15. The method of claim 1 , wherein the target cytokine and the reference cytokine are non-related proteins or sequence-non-related proteins.

16. The method of claim 1 , wherein the degree of coincidence between the 3-dimensional structures of the target cytokine and the reference cytokine is in a region selected from the group consisting of:

(a) a region that is less than about 10%, 15%, 25% of one or both of the two cytokines;

(b) a region that is greater than about 10%, 15% or 25% of one or both of the two cytokines; and

(c) a region that covers the full length of one or both of the two cytokines.

17. The method of claim 1 , wherein the superposition and MS deviation calculations are made using all of the peptide backbone atoms selected from the group consisting of: N, C, C(C═O), O and CA.

18. The method of claim 1 , wherein the superposition and RMS deviation calculations are carried out on a subset of regions or domains of a larger protein that adopts a structure similar to a smaller protein.

19. The method of claim 1 , wherein the degree of coincidence between the 3-dimensional structures of the target cytokine and the reference cytokine is obtained using a method or a combination of two or more methods selected from among: Class Architecture, Topology and Homologous Superfamily (CATH); Combinatorial Extension of the optimal path (CE); Fold Classification based of Structure-Structure Alignment of Proteins (FSSP); Structural Classification of Proteins (SCOP); Vector Alignment Search Tool (VAST), and TOP.