Synthesis of purification tags for optimal downstream processing

Downstream purification yields and costs can be significantly improved by g enetically modifying a product protein to alter its physical properties. Pu rification tags, or sequences of amino acids which are genetically fused on to the product protein, have been extensively researched and used for this purpose. However, all of the work in this area has involved specific purifi cation tags, which have advantages in certain situations but are not generi cally optimal. In this work we describe the development and application of a combinatorial approach which can generate the best sequence of amino acid s for a particular product protein. The aim of the work is to develop an al gorithm which generates sequences of amino acids (i.e. purification tags) w hich may be fused onto a specific product protein and used to aid in subseq uent purification steps. The work is integrated into a previously developed bioprocess synthesis algorithm, which enables us to compare the flowsheets generated with and without purification tags for a case study system. The results show that the approach allows us to synthesise flowsheets with fewe r units, higher yields and lower costs. (C) 2000 Elsevier Science Ltd. All rights reserved.