Affinity chromatography of plasma proteins (guanidinobenzoatase): use of mimetic matrices and mimetic soluble ligands to prevent the binding of albumin on target affinity matrices

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.

Surface-enhanced Raman and steady fluorescence study of interaction between antitumoral drug 9-aminoacridine and trypsin-like protease related to metastasis processes, guanidinobenzoatase

Fluorescence spectroscopy and surface-enhanced Raman spectroscopy (SERS) were applied to study the interaction of the antitumoral drug 9-aminoacridine (9AA) with a trypsin-like protease guanidinobenzoatase (GB) extracted from a mouse Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission was detected in the emission fluorescence spectra at certain drug and enzyme concentrations. A SERS study was accomplished on silver colloids at several excitation wavelengths in order to obtain more information about the interaction mechanism. The results derived from Raman spectroscopy indicated that 9AA in the amino monomeric form may interact with the enzyme by means of two different bonds: an ionic bond with a negatively charged amino acid and a ring stacking interaction with an aromatic residue placed in the catalytic site of GB. This interaction mechanism was responsible for a strong exciplex emission detected at a longer wavelength than the expected value of the normal fluorescence emission. Moreover, the GB concentration dependence of the interaction suggested that the drug was sensitive to the quaternary structure of the enzyme.

Interaction of the antitumor drug 9-aminoacridine with guanidinobenzoatase studied by spectroscopic methods: a possible tumor marker probe based on the fluorescence exciplex emission

Fluorescence spectroscopy, surface-enhanced Raman spectroscopy (SERS), and analytical centrifugation are applied in this work to study the interaction of the antitumor drug 9-aminoacridine (9AA) with a trypsin-like protease, guanidinobenzoatase (GB), extracted from an Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission can be detected at a certain drug and enzyme concentration. The 9AA exciplex emission was also studied for 9AA interacting with others serin proteases: alpha-chymotrypsin, trypsin, and penicillin G-acylase (PGA), as well as with bovine serum albumin (BSA) in order to obtain information about the active center of GB. We have found that the exciplex 9AA emission may be induced by a ring-stacking interaction between the monomeric drug, under the amino form, and an aromatic residue placed in the catalytic site of the protein. The results derived from Raman spectroscopy corroborate this interaction mechanism, as demonstrated by the existence of typical protonated amino 9AA marker bands as well as an important modification of the ring vibrations, thus indicating the existence of an interaction through ring stacking. The analytical centrifugation technique was applied to study the GB association in aqueous solution, demonstrating that the 9AA/GB interaction depends on the enzyme quaternary structure. An interaction of 9AA with an associate form of GB, which may be the actual enzyme active form, is suggested.

Essential role of the concentration of immobilized ligands in affinity chromatography: purification of guanidinobenzoatase on an ionized ligand

Guanidinobenzoatase, a plasma protein with possible application as a 'tumor marker', has been fully purified by one-step affinity chromatography. The affinity matrix was prepared by 'controlled' immobilization of an enzyme inhibitor (agmatine) onto commercial agarose gels containing carboxyl moieties activated as N-hydroxysuccinimide esters. In this way, agmatine becomes immobilized through an amido bond and preserves an ionized guanidino moiety. Different matrices with different concentration of ligands were prepared in order to evaluate their properties as affinity supports. Interestingly, matrices with a very low concentration of immobilized ligands (2 microlmol/ml, corresponding to the modification of only 5% of active groups in the commercial resins) exhibited a low capacity for unspecific adsorption of proteins (as anion-exchange resins) and displayed also a high capacity for specific adsorption of our target protein. On the other hand, when affinity matrices possessed a moderate concentration of agmatine (10 micromol/ml of gel or higher), two undesirable phenomena were observed: (a) the matrix behaves as a very good anionic exchange support able to non-specifically adsorb most of plasma proteins and (b) the specific adsorption of our target protein becomes much lower. The latter phenomenon could be due to steric hindrances promoted by the interaction between each individual immobilized ligand and the corresponding binding pocket in the target protein. These hindrances could also be promoted by the presence of a fairly dense layer of immobilized ligands covering the support surface, thus preventing interactions between immobilized ligands and partially buried protein-binding pockets. In this way, a successful affinity purification (23.5% yield, x220 purification factor, a unique electrophoretic band) could be achieved by combination of three approaches: (i) the use of affinity matrices possessing a very low density of immobilized ligands, (ii) performing affinity adsorption at high ionic strength and (iii) performing specific desorption with substrates or substrate analogues.