A comparison study between polymeric ligand and monomeric ligand for oligopeptide adsorption.

This work aimed to compare two types of affinity ligands, i.e. polymeric and monomeric ligands, by investigating their adsorption affinity, capacity and selectivity to oligopeptide. The peptide NH(2)-VVRGCTWW-COOH (VW-8) was chosen as the target adsorbate, while histidine (His), aspartic acid (Asp), and leucine (Leu) were selected as the ligands, respectively. For each kind of ligand, both monomeric (M) and polymeric (P) forms were introduced onto the Sepharose matrix respectively to obtain the corresponding adsorbents. Both affinity tests using isothermal titration calorimetry (ITC) and adsorption capacities using static adsorption experiments indicated that the adsorbents with polymeric ligands (MX-P) exhibited better adsorption ability for VW-8 than the adsorbents with monomeric ligands (MX-M). In particular, the MX-PHis exhibited its affinity constant of 2.39 × 10(6) M(-1) and its adsorption capacity of 77.4 mg/g for VW-8, which was approximately 8-10 times higher than that of MX-MHis. Such distinct adsorption abilities between polymeric and monomeric ligands were interpreted based on nuclear magnetic resonance (NMR) and ITC data, and the results indicated that such better characters of polymeric ligands were ascribed to their good flexibility which facilitated the cooperative effects as well as the accessibility of ligands to the peptide. Additionally, the selective adsorption experiments indicated that all the adsorbents with polymeric ligands exhibited good selectivity to the peptide VW-8.

Effects of oligopeptide's conformational changes on its adsorption.

We report the effects of peptide adsorption to cross-linked polymers (adsorbents) by its conformational changes. Two adsorbents, APhe and ALeu, were prepared and expected to show high affinity to the oligopeptide VW-8 (NH(2)-Val-Val-Arg-Gly-Cys-Thr-Trp-Trp-COOH) according to our previous studies. These absorbents bared the residues of phenylalanine and leucine, respectively, and carried both hydrophobic and electrical groups. The adsorbent AAsp, which carried only the electrostatic groups, was also prepared as a reference. Both APhe and ALeu were found to exhibit higher VW-8 capacity than AAsp, in which APhe showed the highest VW-8 capacity (13.6 mg/g). The VW-8 adsorption to ALeu and APhe was analyzed using a variety of techniques, including the surface plasmon resonance (SPR) technology, nuclear magnetic resonance (NMR) spectra and isothermal titration calorimetry (ITC). The comprehensive experimental data together indicated that APhe could induce a conformational change of VW-8 from a random-coil to a ß-strand structure due to its ability to provide the strong ring stacking and electrostatic interactions, which is believed to be responsible for its highest adsorption affinity (K(a)=2.59×10(7) M(-1)). In contrast, the hydrophobic interactions provided by ALeu were not strong enough to induce a VW-8 conformational change to a regular structure, and therefore it exhibited a relatively lower affinity to VW-8 (K(a)=6.23×10(5) M(-1)). The results presented in this work showed that peptide adsorption can be influenced by its conformational changes induced by suitable adsorbents via strong non-covalent interactions.