K5 lyase A (KflA) is a tail spike protein (TSP) encoded by a K5A coliphage, which cleaves K5 capsular polysaccharide, a glycosaminoglycan with the repeat unit [-4)-␤GlcA-(1,4)-␣GlcNAc(1-], displayed on the surface of Escherichia coli K5 strains. The crystal structure of KflA reveals a trimeric arrangement, with each monomer containing a right-handed, singlestranded parallel ␤-helix domain. Stable trimer formation by the intertwining of strands in the C-terminal domain, followed by proteolytic maturation, is likely to be catalyzed by an autochaperone as described for K1F endosialidase. The structure of KflA represents the first bacteriophage tail spike protein combining polysaccharide lyase activity with a single-stranded parallel ␤-helix fold. We propose a catalytic site and mechanism representing convergence with the syn-␤-elimination site of heparinase II from Pedobacter heparinus.The KflA protein is a K5 lyase, an enzyme found as a tail spike protein of coliphages K5A (1, 2) and K1-5 (3), where it catalyzes depolymerization of K5 capsular polysaccharide. K5 lyase enables the phage to recognize and remove the protective K5 capsule around host bacteria, thereby exposing phage receptors in the outer membrane. The K5 capsular polysaccharide is a virulence factor of Escherichia coli K5 isolates, which are responsible for extraintestinal infections (4, 5). The polysaccharide is identical to N-acetyl-heparosan (heparan), a structure present in nonmodified regions of heparan sulfate, and KflA has been utilized previously to study the domain structure of heparan sulfate (6). A bacterial K5 lyase, ElmA, from E. coli K5 strain SEBR 3282 also has been described (7).The structures of several bacterial glycosaminoglycan-degrading lyases have been published: hyaluronate lyases (EC 4.2.2.1) and chondroitin AC lyases (EC 4.2.2.5) have catalytic N-terminal domains with (␣/␣) 5 toroid topology and C-terminal ␤-sheet/sandwich domains (8 -10), they act at GlcA residues within their substrates. Chondroitin ABC lyases (11,12) and heparinase II from Pedobacter heparinus (13) have overall structural similarity with these enzymes and can act at GlcA or IdoA (C5-epimerised GlcA) substrate residues, with each enzyme using two overlapping and epimer-specific catalytic groupings (12, 13). A heparin lyase (EC 4.2.2.7, heparinase I) from Bacteroides thetaiotaomicron recently has been shown to have a ␤-jellyroll domain containing an IdoA-specific active site similar to the IdoA-specific site of heparinase II (14). Heparinsulfate lyases (heparitinase or heparinase III, EC 4.2.2.8) act at GlcA residues of suitable substrates (15); no representative structure has yet been published, but these enzymes have sequence homology within the C-terminal ␤-sheet/sandwich domain of heparinase II. Chondroitinase B (EC 4.2.2.4) from Pedobacter heparinus (16, 17) is the only glycosaminoglycan lyase known to contain the right-handed parallel ␤-helix topology that we report here for KflA. It acts at IdoA residues within the substrate dermatan sulfate.The first...

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The objectives of this study were the biosynthesis of silver nanoparticles (NPs) by biotransformations using Saccharomyces cerevisiae and analysis of the sizes and shapes of the NPs produced. Dried and freshly cultured S. cerevisiae were used as the biocatalyst. Dried yeast synthesized few NPs, but freshly cultured yeast produced a large amount of them. Silver NPs were spherical, 2-20 nm in diameter, and the NPs with the size of 5.4 nm were the most frequent ones. NPs were seen inside the cells, within the cell membrane, attached to the cell membrane during the exocytosis, and outside of the cells.

Background & Aims There are some studies indicating the effects of probiotic-containing foods or supplements on viral diseases. We aimed to conduct a rapid review of probiotics with specific emphasis on their potential for early administration in patients at greater risk of SARS-CoV-2 infection. Methods We searched on PubMed, EMBASE, Google Scholar, Science Direct, Scopus and Web of Science up to February 2021 to identify interventional and observational studies documenting the effects of probiotics strains on interleukins, virus titers, and antibody production with a focus on probiotic-containing foods (PROSPERO Registration ID. CRD42020181453). Results From a total of 163 records, 21 studies were classified into three domains based on the efficacy of probiotics on 1) the level of interleukins (n=7), 2) virus titers (n=2), and 3) interferon (IFN) and antibody production (n=12). The suppuration of pro-inflammatory interleukins and type I INF production seemed to be the main anti-viral effect of probiotics. Nine studies also indicated the beneficial effects of probiotics and fermented foods on viral diseases. Conclusion Based on evidence, some probiotic strains may be useful in viral infections; randomized trials are needed to confirm these findings.

Background:For the past 30 years, bacterial L-asparaginases have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. It is found in a variety of organisms such as microbes, plants and mammals. Their intrinsic low-rate glutaminase activity, however, causes serious side-effects, including neurotoxicity, hepatitis, coagulopathy and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side-effects in leukemia therapy. Our aim was to clone, express, purify and characterize E. carotovora asparaginase.Materials and Methods:L-asparaginase from E. carotovora NCYC 1526 (ErA) was cloned and expressed in Escherichia coli strain BL21 (DE3). The enzyme was purified to homogeneity by affinity chromatography. Various conditions were tested to maximize the production of recombinant asparaginase in E. coli.Results:A new L. asparaginase from E. carotovora NCYC 1526 (ErA) was successfully cloned, expressed and purified in E. coli BL21 (DE3). The specific activity of the enzyme was 430 IU/mg.Conclusion:The results of the present work form the basis for a new engineered form of ErA for future therapeutic use, which could be extended with crystallographic studies.