IMMUNOGLOBULIN VARIABLE DOMAINS
VH domain, in which: (i) the amino acid residue at position 112 is one of K or Q; and/or (ii) the amino acid residue at position 89 is T; and/or (iii) the amino acid residue at position 89 is L and the amino acid residue at position 110 is one of K or Q; and (iv) in each of cases (i) to (iii), the amino acid at position 11 is preferably V; and in which said VH domain contains a C-terminal extension (X)n, in which n is 1 to 10, preferably 1 to 5, such as 1, 2, 3, 4 or 5 (and preferably 1 or 2, such as 1); and each X is an (preferably naturally occurring) amino acid residue that is independently chosen, and preferably independently chosen from the group consisting of alanine (A), glycine (G), valine (V), leucine (L) or isoleucine (I).
1 .- 72 . (canceled)
73 . A nucleic acid encoding a heavy chain immunoglobulin single variable domain (ISVD), wherein the heavy-chain ISVD comprises an amino acid residue K or Q at Kabat position 112.
74 . The nucleic acid of claim 73 , wherein the heavy chain ISVD comprises a C-terminal sequence (Kabat positions 109 to 113) that is VTVKS (SEQ ID NO:1) or VTVQS (SEQ ID NO:2), or a sequence that has one amino acid difference at one of Kabat positions 109, 110, 111 or 113 with either the sequence VTVKS and/or VTVQS and that still has either the amino acid residue K or Q at Kabat position 112.
75 . The nucleic acid of claim 73 , wherein the heavy chain ISVD comprises an amino acid residue L, E, K, V, or Y at Kabat position 11.
76 . The nucleic acid of claim 73 , wherein the heavy chain ISVD comprises an amino acid residue E at Kabat position 11 and an amino acid residue K at Kabat position 112.
77 . The nucleic acid of claim 73 , wherein the heavy chain ISVD comprises an amino acid residue L at Kabat position 108.
78 . The nucleic acid of claim 73 , wherein the heavy chain ISVD has a framework 4 (FW4 sequence) that is either:
a) one of the FW4 sequences of SEQ ID NOs: 3 to 5, 7 to 14, 16 to 20; or
b) a sequence that has no more than three amino acid differences with at least one of the FW4 sequences of SEQ ID NOs 3 to 5, 7 to 14, 16 to 20, in which the amino acid residue at Kabat position 112 is K or Q.
79 . The nucleic acid of claim 78 , wherein the heavy chain ISVD has a FW4 sequence that is either:
a) WGQGTQVTVKS (SEQ ID NO:3) or WGQGTQVTVQS (SEQ ID NO:12); or
b) a sequence that has no more than three amino acid differences with SEQ ID NO:3 and/or SEQ ID NO: 12, in which the amino acid residue at Kabat position 112 is K or Q.
80 . The nucleic acid of claim 73 , wherein the heavy chain ISVD has a framework 4 (FW4 sequence) that is one of the FW4 sequences of SEQ ID NOs: 3 to 5, 7 to 14, 16 to 20.
81 . The nucleic acid of claim 80 , wherein the heavy chain ISVD has a FW4 sequence that is WGQGTQVTVKS (SEQ ID NO:3) or WGQGTQVTVQS (SEQ ID NO:12).
82 . The nucleic acid of claim 73 , wherein the heavy chain ISVD comprises an amino acid residue S, T, A, L, P, F, E, or V at Kabat position 113.
83 . The nucleic acid of claim 73 , wherein the heavy chain ISVD specifically binds to human serum albumin.
84 . The nucleic acid of claim 83 , wherein the heavy chain ISVD comprises: a CDR1 having the amino acid sequence SFGMS (SEQ ID NO:41); a CDR2 having the amino acid sequence SISGSGSDTLYADSVKG (SEQ ID NO:42); and a CDR3 having the amino acid sequence GGSLSR (SEQ ID NO:43).
85 . The nucleic acid of claim 73 , wherein the heavy chain ISVD is linked at its C-terminal end to another amino acid sequence, moiety, domain or binding unit, optionally via a suitable linker.
86 . The nucleic acid of claim 73 , wherein the heavy chain ISVD is linked at its C-terminal end to another immunoglobulin single variable domain, optionally via a suitable linker.
87 . The nucleic acid of claim 73 , wherein the heavy chain ISVD is linked, at its C-terminal end, to a C-terminal extension (X) n , in which n is 1 to 5; and each X is an amino acid residue that is independently chosen.
88 . The nucleic acid of claim 73 , wherein the heavy chain ISVD is a VHH domain, a humanized VHH domain or a camelized VH domain.
89 . A library comprising one or more nucleic acids according to claim 73 .
90 . The library of claim 89 , wherein the library comprises at least 100 different sequences.
91 . The library of claim 89 , wherein the library is an expression library.
92 . The library of claim 89 , wherein the library is a synthetic library.
93 . A host cell comprising an expression vector comprising the nucleic acid sequence of claim 73 .
94 . A method for producing a heavy chain ISVD comprising expressing a nucleic acid sequence encoding the heavy chain ISVD in a host cell according to claim 93 .