Free polymeric bioligands in aqueous two-phase affinity extractions of microbial xylanases and pullulanase

Applications of Alginate in Bioseparation of Proteins

Alginate is a polysaccharide that is a block polymer consisting of block units of guluronic acid and mannuronic acid. It shows inherent biological affinity for a variety of enzymes such as pectinase, lipase, phospholipase D, a and ss amylases and glucoamylase. Taking advantage of its precipitation with Ca2+ and the above-mentioned property, alginate has been used for purification of these enzymes by affinity precipitation, aqueous two phase separation, macroaffinity ligand facilitated three phase partitioning, immobilized metal affinity chromatography and expanded bed affinity chromatography. Thus, this versatile marine resource has tremendous potential in bioseparation of proteins.

The affinity concept in bioseparation: Evolving paradigms and expanding range of applications

The meaning of the word affinity in the context of protein separation has undergone evolutionary changes over the years. The exploitation of molecular recognition phenomenon is no longer limited to affinity chromatography modes. Affinity based separations today include precipitation, membrane based purification and two-phase/three-phase extractions. Apart from the affinity ligands, which have biological relationship (in vivo) with the target protein, a variety of other ligands are now used in the affinity based separations. These include dyes, chelated metal ions, peptides obtained by phage display technology, combinatorial synthesis, ribosome display methods and by systematic evolution of ligands by exponential enrichment (SELEX). Molecular modeling techniques have also facilitated the designing of biomimetic ligands. Fusion proteins obtained by recombinatorial methods have emerged as a powerful approach in bioseparation. Overexpression in E. coli often result in inactive and insoluble inclusion bodies. A number of interesting approaches are used for simultaneous refolding and purification in such cases. Proteomics also needs affinity chromatography to reduce the complexity of the system before analysis by electrophoresis and mass spectrometry are made. At industrial level, validation, biosafety and process hygiene are also important aspects. This overview looks at these evolving paradigms and various strategies which utilize affinity phenomenon for protein separations.

Chitosan as a macroaffinity ligand

(1) Chitosan was found to be a suitable macroaffinity ligand for affinity precipitation of chitinase from Neurospora crassa, cabbage and puffballs. (2) The activity recoveries of 85, 82 and 90% with concomitant fold purifications in terms of specific activities were 27, 15 and 30 with N. crassa, cabbage and puffballs and were obtained with affinity precipitation. These results were obtained with clarified extracts/homogenates as the starting materials. (3) The incorporation of chitosan in poly(ethylene glycol) (PEG)-salt aqueous two-phase system allowed purification of chitinases from these sources directly from unclarified extracts/homogenates. (4) The 96% (w/v) chitosan (of initially introduced into the aqueous two-phase system) partitioned into PEG-phase and this enhanced the partitioning of chitinases into PEG-phase. The chitosan, free as well as bound to chitinases, could be separated from PEG-phase by increasing the pH to 7. (5) By the process of desorption with 2.0 M MgCl2, 86, 80 and 88% activity recoveries (% expressed in terms of total units of enzyme activities in the crude extract) were obtained in the case of N. crassa, cabbage and puffballs, respectively. The corresponding fold purifications in terms of specific activities were 34, 20 and 38. (6) The purified preparations gave single bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the estimated molecular masses agreed with the reported values in the literature.

Purification of phospholipase D by two-phase affinity extraction

An aqueous two-phase system of polyethylene glycol (PEG)-salt was used for purification of phospholipase D (PLD) from peanuts and carrots. Alginate, a known macroaffinity ligand for PLD, was incorporated in the PEG phase and resulted in 91 and 93% of the enzyme activity (from peanuts and carrots, respectively) getting partitioned in the PEG phase. The elution of the enzyme from alginate was facilitated by exploiting the fact that the latter can be reversibly precipitated in the presence of Ca2+. The enzyme was eluted from the polymer by using 0.5 M NaCl. Peanuts and carrots PLD could be purified 78- and 17-fold with 82 and 85% activity recovery, respectively. The purified enzyme from both sources gave a single band on sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) electrophoresis.

Smart Polymeric Materials

Smart polymeric materials respond with a considerable change in their properties to small changes in their environment. Environmental stimuli include temperature, pH, chemicals, and light. "Smart" stimuli-sensitive materials can be either synthetic or natural. This review discusses the application of smart materials as tools to solve biological problems such as bioseparation, drug delivery, biosensor design, tissue engineering, protein folding, and microfluidics. The goal for these endeavors is to mimic the "smartness" of biological systems and ultimately moderate complex systems such as immune responses at desired levels. The versatility and untapped potential of smart polymeric materials makes them one of the most exciting interfaces of chemistry and biology.

kappa-Carrageenan as a new smart macroaffinity ligand for the purification of pullulanase

kappa-Carrageenan is a polysaccharide from red seaweed which gets precipitated by K+ ions and dissolves again in water. This smart, K(+)-responsive polymer was found to selectively bind pullulanase activity from Bacillus acidopullulyticus. Gel filtration on Sephadex G-200 showed the formation of the polymer-pullulanase complex at the pre-precipitation stage. On the other hand, phospholipase D, an enzyme which did not co-precipitate with kappa-carrageenan, did not form any complex with the polymer. Thus, K+ ions could be used to selectively precipitate the pullulanase activity. Then, 92% enzyme activity could be eluted with 1 M maltose solution. The single step protocol resulted in 50-fold purification, with a single band on sodium dodecylsulfate-polyacrylamide gel electrophoresis.

Macroaffinity ligand-facilitated three-phase partitioning for purification of glucoamylase and pullulanase using alginate

Starch-degrading enzymes glucoamylase (from Aspergillus niger), and pullulanase (from Bacillus acidopullulyticus) were purified using alginates (polysaccharides consisting of mannuronic acids and guluronic acids) by a recently developed technique called macroaffinity ligand-facilitated three-phase partitioning (MLFTPP). In this process, a crude preparation of the enzyme was mixed with alginate. On addition of appropriate amounts of ammonium sulfate and t-butanol, the alginate bound enzyme appeared as an interfacial precipitate between the lower aqueous and the upper t-butanol phase. Enzyme activity from this interfacial precipitate was recovered using 1M maltose. Glucoamylase and pullulanase were purified 20- and 38-fold with 83% and 89% activity recovery, respectively. Both the purified preparations showed a single band on SDS-PAGE.