Immobilized zinc affinity chromatography of pectin hydroxamic acids for purification of trypsin inhibitors from soybean and sweet potato

Physico-Chemical and Antifungal Properties of a Trypsin Inhibitor from the Roots of Pseudostellaria heterophylla

Plant peptidase inhibitors play essential roles in the defense systems of plants. A trypsin inhibitor (PHTI) with a molecular mass of 20.5 kDa was isolated from the fresh roots of the medicinal herb, Pseudostellaria heterophylla. The purification process involved ammonium sulfate precipitation, gel filtration chromatography on Sephadex G50, and ion-exchange chromatography on DEAE 650M. The PHTI contained 3.7% α-helix, 42.1% β-sheets, 21.2% β-turns, and 33% disordered structures, which showed similarity with several Kunitz-type trypsin inhibitors. Inhibition kinetic studies indicated that PHTI was a competitive inhibitor, with a Ki value of 3.01 × 10-9 M, indicating a high affinity to trypsin. The PHTI exhibited considerable stability over a broad range of pH (2⁻10) and temperatures (20⁻70 °C); however, metal ions, including Fe3+, Ba2+, Mn2+, and Al3+, could inactivate PHTI to different degrees. Results of fluorescence spectroscopy and circular dichroism showed that Fe3+ could bind to TI with an association constant of 2.75 × 10⁵ M-1 to form a 1:1 complex, inducing conformation changes and inactivation of PHTI. In addition, PHTI could inhibit the growth of the phytopathogens, Colletotrichum gloeosporioides and Fusarium oxysporum, through disruption of the cell membrane integrity. The present study extended research on Pseudostellaria heterophylla proteins and makes PHTI an exploitable candidate as an antifungal protein for further investigation.

One-pot preparation of silica-supported hybrid immobilized metal affinity adsorbent with macroporous surface based on surface imprinting coating technique combined with polysaccharide incorporated sol–gel process

A simple and reliable one-pot approach using surface imprinting coating technique combined with polysaccharide incorporated sol-gel process was established to synthesize a new organic-inorganic hybrid matrix possessing macroporous surface and functional ligand. Using mesoporous silica gel being a support, immobilized metal affinity adsorbent with a macroporous shell/mesoporous core structure was obtained after metal ion loading. In the prepared matrix, covalently bonded coating and morphology manipulation on silica gel was achieved by using one-pot sol-gel process starting from an inorganic precursor, <gamma>-glycidoxypropyltrimethoxysiloxane (GPTMS), and a functional biopolymer, chitosan (CS) at the atmosphere of imprinting polyethylene glycol (PEG). Self-hydrolysis of GPTMS, self-condensation, and co-condensation of silanol groups (Si-OH) from siloxane and silica gel surface, and in situ covalent cross-linking of CS created an orderly coating on silica gel surface. PEG extraction using hot ammonium hydroxide solution gave a chemically and mechanically stabilized pore structure and deactivated residual epoxy groups. The prepared matrix was characterized by using X-ray energy dispersion spectroscopy (EDX), scanning electron microscopy (SEM) and mercury intrusion porosimetry. The matrix possessed a high capacity for copper ion loading. Protein adsorption performance of the new immobilized metal affinity adsorbent was evaluated by batch adsorption and column chromatographic experiment using bovine serum albumin (BSA) as a simple model protein. Under the optimized coating conditions, the obtained macroporous surface resulted in a fast kinetics and high capability for protein adsorption, while the matrix non-charged with metal ions offered a low non-specific adsorption.