Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Designing monoclonal antibody fragment-based affinity resins with high binding capacity by thiol-directed immobilisation and optimisation of pore/ligand size ratio

Monoclonal antibody (mAb) based affinity resins usually suffer from low binding capacity, most probably as a result of steric hindrance by the large 150kDa size of the mAb and a random immobilisation approach. The present work investigates the influence of a variety of factors on dynamic binding capacity (DBC) such as pore/ligand size ratio, accessibility of ligand and ligand density. The effect of pore/ligand size ratio was investigated using Fab and scFv fragments on various resins with different pore sizes. The accessibility of the ligand was investigated by a site-directed immobilisation approach, where three C-terminal tags, PPKPPK, FLAG™ and Cys, were introduced into the Fab fragments for immobilisation on resins via amino-, carboxyl- and thiol-groups, respectively. The scFv fragments were tagged at the C-terminal only with FLAG™ to enable a straight forward purification procedure, and were immobilised to resins via amino- and carboxyl-groups. The target protein had a molecular weight (MW) of 50kDa. A 3-fold higher dynamic binding capacity at 100% breakthrough (DBC_100%) was observed for Fab wild-type (wt) on CNBr-activated Sepharose 4 FF relative to mAb on same resin at the same ligand density. However, no major difference in DBC_100% was observed between Fab wt and scFv immobilised on CNBr-activated Sepharose 4 FF at the same ligand density. Thus, further increase of pore/ligand size ratio from Fab to scFv on a resin with average pore size of 300Å, did not seem to be beneficial. Among the tested tags, only the C-terminal Cys tag proved to site-direct the ligands during immobilisation as it allowed the DBC_100% to increase 1.6-fold as compared to Fab wt immobilised via amino-groups on CNBr-activated Sepharose 4 FF and Actigel ALD Superflow at the same ligand density. The influence of ligand density was investigated by selecting immobilised Fab Cys on Sulfhydryl-reactive resin. Increasing ligand density from 0.103 to 0.202μmol/mL resulted in the same utilisation yield (82-85%), whereas a further increase in ligand density from 0.202 to 0.328μmol/mL resulted in a 20%-unit decrease in utilisation yield and less steep breakthrough curve, suggesting steric hindrance in the pores of the resin. In addition, site-directed affinity ligands resulted in a more pronounced, sigmoid-shaped breakthrough curve, leading to more efficient use of capacity. The highest DBC_100% was obtained for Fab Cys on Sulfhydryl-reactive resin and scFv on Actigel ALD Superflow; 11mg/mL and 10mg/mL, respectively, as compared to the DBC_100% of 0.8mg/mL for mAb on CNBr-activated Sepharose 4 FF. Pore/ligand size ratio of 3, which was achieved for Fab ligands on the studied resins, was shown to be feasible for capturing a protein in MW of 50kDa. Totally, a 13.8-fold improvement in DBC_100% was achieved with the Fab-based affinity resin coupled via the C-terminal Cys as compared to the mAb-based affinity resin.

Cellulose carbonates: a platform for promising biopolymer derivatives with multifunctional capabilities

Cellulose carbonates as a platform compound open new possibilities for the design of advanced materials based on the most important renewable resource cellulose. In the present feature, the chemistry of cellulose carbonates is discussed considering own research results adequately. After a short overview about methods for activation of polysaccharides for a conversion with nucleophilic compounds in particular with amines, details about various methods for the synthesis of polysaccharide carbonates are discussed. The main issue of the feature is the synthesis and aminolysis of cellulose carbonates with low, intermediate, and high degree of substitution and the evaluation of this chemistry with respect to specific challenges. Functional cellulose carbamates, obtained from cellulose phenyl carbonate by aminolysis, show the potential use of this class of celluloses. Immunoassays and zwitterionic polymers are included as representative examples regarding properties and application of the new cellulose-based products.