The present invention is directed to a protein purification construct having three tandem, coupled segments composed of a binding protein, an interconnecting linker and a variable fused polypeptide which incorporates the one or more copies of a product peptide. The binding protein is a mammalian or human carbonic anhydrase, or a modified version of the carbonic anhydrase. The protein purification construct may be employed in methods for expression of the product peptide in microbial and higher organism and for ligand immobilized affinity purification of the product peptide.