Enzymes, Biocatalysis and Chemical Biology

Purification and characterization of L-arginine deiminase from Penicillium chrysogenum

L-arginine deiminase (ADI, EC 3.5.3.6) hydrolyzes arginine to ammonia and citrulline which is a natural supplement in health care. ADI was purified from Penicillium chrysogenum using 85% ammonium sulfate, DEAE-cellulose and Sephadex G200. ADI was purified 17.2-fold and 4.6% yield with a specific activity of 50 Umg- 1 protein. The molecular weight was 49 kDa. ADI expressed maximum activity at 40oC and an optimum pH of 6.0. ADI thermostability was investigated and the values of both t0.5 and D were determined. Kd increased by temperature and the Z value was 38oC. ATP, ADP and AMP activated ADI up to 0.6 mM. Cysteine and dithiothreitol activated ADI up to 60 µmol whereas the activation by thioglycolate and reduced glutathione (GSH) prolonged to 80 µmol. EDTA, α,α-dipyridyl, and o-phenanthroline inactivated ADI indicating that ADI is a metalloenzyme. N-ethylmaleimide (NEM), N-bromosuccinimide (NBS), butanedione (BD), dansyl chloride (DC), diethylpyrocarbonate (DEPC) and N-acetyl-imidazole (NAI) inhibited ADI activity indicating the necessity of sulfhydryl, tryptophanyl, arginyl, lysyl, histidyl and tyrosyl groups, respectively for ADI catalysis. The obtained results show that ADI from P. chrysogenum could be a potential candidate for industrial and biotechnological applications.

Study on the Interaction Mechanism of Methoxy Polyethylene Glycol Maleimide with Sweet Potato β-Amylase

In this study, sweet potato β-amylase (SPA) was modified by methoxy polyethylene glycol maleimide (molecular weight 5000, Mal-mPEG5000) to obtain the Mal-mPEG5000-SPA modified β-amylase and the interaction mechanism between SPA and Mal-mPEG5000 was investigated. the changes in the functional groups of different amide bands and modifications in the secondary structure of enzyme protein were analyzed using infrared spectroscopy and circular dichroism spectroscopy. The addition of Mal-mPEG5000 transformed the random curl in the SPA secondary structure into a helix structure, forming a folded structure. The Mal-mPEG5000 improved the thermal stability of SPA and protected the structure of the protein from breaking by the surrounding. The thermodynamic analysis further implied that the intermolecular forces between SPA and Mal-mPEG5000 were hydrophobic interactions and hydrogen bonds due to the positive values of ΔH^θ and ΔS^θ. Furthermore, the calorie titration data showed that the binding stoichiometry for the complexation of Mal-mPEG5000 to SPA was 1.26, and the binding constant was 1.256 × 10⁷ mol/L. The binding reaction resulted from negative enthalpy, indicating that the interaction of SPA and Mal-mPEG5000 was induced by the van der Waals force and hydrogen bonding. The UV results showed the formation of non-luminescent material during the interaction, the Fluorescence results confirmed that the mechanism between SPA and Mal-mPEG5000 was static quenching. According to the fluorescence quenching measurement, the binding constant (K_A) values were 4.65 × 10⁴ L·mol^-1 (298K), 5.56 × 10⁴ L·mol^-1 (308K), and 6.91 × 10⁴ L·mol^-1 (318K), respectively.

The Encounter of Biomolecules in Metal-Organic Framework Micro/Nano Reactors

In nature, biochemical reactions often take place in confined spaces, as typically exemplified by cells. As numerous cellular reactors can be integrated to maintain the living system, researchers have made constant efforts to construct cell-like structures for achieving similar transformations in vitro. Micro/nano reactors engineered by polymers and colloids are becoming popular and being applied in many fields, especially there has been an increasing trend toward constructing metal-organic framework (MOF) micro/nano reactors with the thriving of MOF nanotechnologies. Because of the uniform pores of MOFs, the transmission of substances can be regulated more accurately. Along with properties of large specific surface area, functional diversity and precise control of the particle size, MOFs are also ideal platforms for building distinct microenvironments for biological substances. Compared with traditional polymersomes and colloidosomes, the unique characteristics of MOFs render them potent micro/nano reactor shell materials, mimicking cells for applications in enzymatic catalysis, sensing, nanotherapy, vaccine, biodegradation, etc. This review highlights recent signs of progress on the design of MOF micro/nano reactors and their applications in biology, discusses the existing problems, and prospects their promising properties for smarter multifunctional applications.