Synthetic immunoglobulin domains with binding properties engineered in regions of the molecule different from the complementarity determining regions
Libraries of immunoglobulins which each have one or more amino acid modifications in at least one structural loop region of such immunoglobulins, where the modified loop region specifically binds to an epitope of an antigen to which an unmodified immunoglobulin does not significantly bind.
1. An isolated nucleic acid encoding a polypeptide scaffold comprising an immunoglobulin fold of a constant domain comprising six structural loops connected by beta strands, three of said six structural loops corresponding to three structural loops of a native human IgG1 constant region CH3 domain, said three structural loops of said native human IgG1 constant region CH3 domain consisting of the AB loop (positions 17-19 of SEQ ID NO:1), the CD loop (positions 44-47 of SEQ ID NO:1), and the EF loop (positions 71-73 and 76-77 of SEQ ID NO:1),
wherein said scaffold comprises an amino acid sequence which is at least 80% identical to said native human IgG1 constant region CH3 domain; and
wherein said scaffold comprises a minimum number of residues which differ from corresponding residues of SEQ ID NO: 1 selected from the group consisting of:
a) wherein two or more of said three structural loops of said scaffold comprise a total of at least three residues which are different from corresponding residues of SEQ ID NO: 1;
and/or
b) wherein one of said three structural loops of said scaffold comprise at least four residues which are different from corresponding residues of SEQ ID NO: 1; and
wherein said structural loops of (a) and (b) of said polypeptide scaffold form a solvent accessible surface.
2. The nucleic acid of claim 1 , wherein scaffold comprises an amino acid sequence which is at least 85% identical to said native human IgG1 constant region CH3 domain.
3. The nucleic acid of claim 1 , wherein scaffold comprises an amino acid sequence which is at least 90% identical to said native human IgG1 constant region CH3 domain.
4. The nucleic acid of claim 1 , wherein in (a) each of said two or more of said three structural loops of said scaffold comprises at least three residues which are different from corresponding residues of SEQ ID NO: 1.
5. The nucleic acid of claim 1 , wherein said structural loops of (a) and (b) of claim 1 do not comprise an inserted peptide of predetermined sequence that specifically binds an epitope independently of its insertion into said structural loops of (a) and/or (b).
6. The nucleic acid of claim 1 , wherein said scaffold comprises an amino acid sequence selected from the group consisting of: SEQ ID NO: 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40 and 42.
7. A host cell comprising the nucleic acid of claim 1 .
8. A vector comprising the nucleic acid of claim 1 .
9. The vector of claim 8 , wherein said vector is an expression vector.
10. The host cell of claim 7 , wherein said host cell is selected from the group consisting of mammalian cells, plant cells, bacteria, insect cells, and yeast.
11. The host cell of claim 10 , wherein said bacteria is Bacillus subtilis or Escherichia coli.
12. The host cell of claim 10 , wherein said yeast is Pichia pastoris or Saccharomyces cerevisiae.
13. The vector of claim 8 , wherein said vector is a viral vector or a phage vector.