The fungal secondary metabolite patulin is a mycotoxin widespread in foods and beverages which poses a serious threat to human health. However, no enzyme was known to be able to degrade this mycotoxin. For the first time, we discovered that a manganese peroxidase (MrMnP) from Moniliophthora roreri can efficiently degrade patulin. The MrMnP gene was cloned into pPICZα(A) and then the recombinant plasmid was transformed into Pichia pastoris X-33. The recombinant strain produced extracellular manganese peroxidase with an activity of up to 3659.5 U/L. The manganese peroxidase MrMnP was able to rapidly degrade patulin, with hydroascladiol appearing as a main degradation product. Five mg/L of pure patulin were completely degraded within 5 h. Moreover, up to 95% of the toxin was eliminated in a simulated patulin-contaminated apple juice after 24 h. Using Escherichia coli as a model, it was demonstrated that the deconstruction of patulin led to detoxification. Collectively, these traits make MrMnP an intriguing candidate useful in enzymatic detoxification of patulin in foods and beverages.

Acetylated glucuronoxylan is one of the most common types of hemicellulose in nature. The structure is formed by a β-(1→4)-linked D-xylopyranosyl (Xylp) backbone that can be substituted with an acetyl group at O-2 and O-3 positions, and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Acetyl xylan esterases (AcXE) that target mono- or doubly acetylated Xylp are well characterized; however, the previously studied AcXE from Flavobacterium johnsoniae (FjoAcXE) was the first to remove the acetyl group from 2-O-MeGlcpA-3-O-acetyl-substituted Xylp units, yet structural characteristics of these enzymes remain unspecified. Here, six homologs of FjoAcXE were produced and three crystal structures of the enzymes were solved. Two of them are complex structures, one with bound MeGlcpA and another with acetate. All homologs were confirmed to release acetate from 2-O-MeGlcpA-3-O-acetyl-substituted xylan, and the crystal structures point to key structural elements that might serve as defining features of this unclassified carbohydrate esterase family. Enzymes comprised two domains: N-terminal CBM domain and a C-terminal SGNH domain. In FjoAcXE and all studied homologs, the sequence motif around the catalytic serine is Gly-Asn-Ser-Ile (GNSI), which differs from other SGNH hydrolases. Binding by the MeGlcpA-Xylp ligand is directed by positively charged and highly conserved residues at the interface of the CBM and SGNH domains of the enzyme.

Engineering of protein oligomeric state or quaternary structure is a promising approach to adjust proteins for utilization in different applications and research. This study provides a detailed investigation of oligomerization within IlvD/EDD superfamily. A large 255 kDa tetrameric protein of the IlvD/EDD superfamily, L-arabinonate dehydratase from Rhizobium leguminosarum bv. trifolii, was engineered to create a dimeric form containing the [2Fe-2S] catalytic center. Four variants, which contain mutations at two locations of the dimer-dimer interface, were produced. The mutants were analyzed using UV-vis and native mass spectrometry, while iron composition and enzymatic activity with five substrates were also investigated. The three variants with mutations closer to the catalytic center showed a color change with shifted maximum absorption at 455 nm and had reduced catalytic activity. One of the variants, D39K, located farther from the active center, maintained a similar color to the wild-type enzyme. The D39K had a mild decline in the catalytic activity, and it existed in dimeric form. The three-dimensional structure analysis suggests that the D39K mutation disrupted a larger ionic-interaction network on the protein surface, thus preventing the formation of the tetramer.

The worldwide imposed lockdowns forced schools and universities to digitise conventional teaching in a very short time and to convert teaching and learning formats partially or completely to Distance Learning. With 22 double blind peerreviewed articles of researchers reporting on 17 different countries, the editors of this book want to shed light on the effects of Distance Learning in different regions of the world.