Engineered mature domain of human activin A (Uniprot: P08476) expressed in E.coli, refolded and purified to homogeneity. This engineered form of Activin A incorporates an N-terminal truncation to remove a disulphide-linked extension. The resulting protein is optimised for extremely consistent high yield with no observed changes in bioactivity compared to the wild-type. This form is particularly suitable for larger scale culture processes. The mature engineered protein is a disulphide-linked dimer with a molecular weight of 24 kDa.