Albumin variants and conjugates

Abstract

Based on the three-dimensional structure of albumin, the inventors have designed variant polypeptides (muteins) which have one or more cysteine residues with a free thiol group (hereinafter referred to as “thio-albumin”). The variant polypeptide may be conjugated through the sulphur atom of the cysteine residue to a conjugation partner such as a bioactive compound.

1 ) A method of preparing a conjugation-competent polypeptide, comprising:
 a) providing a three-dimensional model comprising at least one instance of an albumin sequence and, optionally, providing an amino acid sequence of that albumin sequence,   b) selecting an amino acid residue in the albumin sequence which corresponds to the first, second, third, fourth or fifth residue relative to the N- or C-terminus of the sequence of the model or of the amino acid sequence or which in each instance of the albumin sequence, relating to the three-dimensional model, fulfills the following conditions:
 i) solvent surface accessibility of at least 80%; 
 ii) B-factor score of at least 30; 
 iii) no polymorphism known to cause thermal instability; 
   c) substituting the selected residue with Cysteine or inserting Cysteine at the N-side or C-side of the selected residue,   d) optionally, making additional alterations to the albumin sequence where each alteration is an amino acid deletion, substitution, or insertion, and   e) preparing a polypeptide having the resulting amino acid sequence.