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Silvaggi, N. R.

Publications and source records attributed to Silvaggi, N. R..

4 recordsLinked to original sources

Computational Prediction of Recombinant Expression Efficiency for Industrial Enzymes: An Integrated Co-Translational Sequence Analysis Platform

Industrial biocatalysis relies on the cost effective production of active enzymes in heterologous hosts, yet a substantial fraction of candidate sequences fails during recombinant expression because sequence-level determinants of translational efficiency are not captured by conventional codon optimization alone. Here we present an integrated computational platform for pre-clinical assessment of industrial enzyme expression potential that combines baseline sequence metrics with co-translational modeling of ribosome stalling, translation rhythm, codon harmonization, folding bottlenecks, solubility proxies, and proteolysis risk. The platform accepts DNA, protein, FASTA, and PDB inputs and returns interpretable expression risk assessments, component-level diagnostics, variant design proposals, and actionable engineering recommendations. Analyses are parameterized for industrial expression hosts (Escherichia coli, Saccharomyces cerevisiae, Bacillus subtilis, and mammalian cells) and for native enzyme sources including Streptomyces, Bacillus, filamentous fungi, actinomycetes, and extremophiles. All analyses execute locally without dependence on external databases, enabling rapid and secure screening of proprietary enzyme candidates prior to gene synthesis and fermenter scale-up. We report three layers of preliminary validation on small cohorts: (i) a retrospective public industrial-enzyme ranking benchmark (n = 20; rank subset n = 10); (ii) calibration of the solubility module on held-out eSOL enzymes with quantitative experimental solubility; and (iii) an independent collaborator wet-lab construct set retained as a true external-test holdout and never used for model fitting (n = 38 labeled constructs). On the external holdout, solubility calls achieved accuracy 68.4% (95% CI 52.5 - 80.9%), sensitivity 56.5% (36.8 - 74.4%), specificity 86.7% (62.1 - 96.3%), balanced accuracy 71.6% (bootstrap 95% CI 57.4 - 84.4%), and MCC 0.43 (0.15 - 0.69). Sensitivity remains close to chance on this small set, whereas specificity is higher; intervals are wide and the evidence should be read as directional rather than definitive. A directional arginine-surface redesign example (SrMilN insoluble parent to SrMilN_SASAR partially soluble variant; incomplete rescue with multiple soluble bands) was recovered. These findings support preliminary screening utility and transparent experimental agreement, but do not constitute high-accuracy prediction of industrial fermenter titre. Offline EC-class heuristics are retained only as optional provisional labels and are not presented as a validated platform capability (agreement 3/20 = 15%, 95% CI 5.2 - 36%; chance for six classes is 16.7%).

bioinformatics↗

Structural and Preliminary Biochemical Characterization of MppQ, a PLP-Dependent Aminotransferase from Streptomyces hygroscopicus

MppQ is an enzyme of unknown function from Streptomyces hygroscopicus that is involved in the biosynthesis of the nonproteinogenic amino acid L-enduracididine (L-End). Since L-End is a component of several peptides showing high activity against methicillin-resistant Staphylococcus aureus (MRSA), a complete understanding of its biosynthetic pathway is of utmost importance for developing chemoenzymatic routes for syntheses of novel antibiotics. In this work, we report high-resolution X-ray crystal structures of MppQ complexed with pyridoxal-5-phosphate (PLP) and pyridoxamine-5-phosphate (PMP). The structure of MppQ shares a fold with known Type I PLP-dependent aminotransferases, consisting of an N-terminal extension, large domain, and a small domain. We also report the first functional characterization of MppQ, which we incubated with enzymatically produced 2-ketoenduracidine and observed conversion to L-End via mass spectroscopy. Additionally, we have observed that MppQ has a relatively high affinity for 2-ketoarginine, a shunt product in the L-End biosynthetic pathway, indicating a possible role of MppQ in increasing efficiency of L-End biosynthesis by converting 2-ketoarginine back to the starting material, L-arginine.

biochemistry↗

Engineering a more specific E. coli glyoxylate/hydroxypyruvate reductase for coupled steady state kinetics assays

The E. coli glyoxylate reductase/hydroxypyruvate reductase A (EcGhrA) was investigated as a coupling enzyme to monitor the transamination of 2-ketoarginine and glycine by the L-enduracididine biosynthetic enzyme MppQ. Surprisingly, 2-ketoarginine proved to be an efficient substrate for EcGhrA. Since the promiscuity of EcGhrA prevented its use as a coupling enzyme to monitor the aminotransferase activity of MppQ, we set about engineering a more specific variant. X-ray crystal structures of EcGhrA were determined in the unliganded state, as well as with glyoxylate and 2-ketoarginine bound. The electron density maps of EcGhrA with 2-ketoarginine bound showed weak electron density for the side chain of this substrate, complicating the choice of active site residues to target for site-directed mutagenesis. The structure of the complex did, however, suggest that the side chain of W45 could interact with the guanidinium group of 2-ketoarginine. We therefore generated the EcGhrAW45F variant and tested it for activity with 2-ketoarginine, glyoxylate, oxaloacetate, -ketoglutarate, -oxofuranacetic acid, phenyl pyruvate, 3-mercaptopyruvate and 2-ketobutyric acid. The W45F variant exhibited a [~]10-fold decrease in the specificity constant (kcat/KM) for 2-ketoarginine, while the reaction with glyoxylate was not significantly impaired. The reactions of the W45F variant with the alternative substrates oxaloacetate and -ketoglutarate were also impaired. Thus, the W45F variant is a less promiscuous enzyme than the wild-type. This engineered EcGhrAW45F variant could be generally useful as a coupling system for enzymes that produce glyoxylate, such as 4-hydroxy-2-oxoglutarate aldolase or isocitrate lyase.

biochemistry↗

Variable Macro X Domain of SARS-CoV-2 Retains the Ability to Bind ADP-ribose

The virus that causes COVID-19, SARS-CoV-2, has a large RNA genome that encodes numerous proteins that might be targets for antiviral drugs. Some of these proteins, such as the RNA-dependent RNA polymers, helicase and main protease, are well conserved between SARS-CoV-2 and the original SARS virus, but several others are not. This study examines one of the proteins encoded by SARS-CoV-2 that is most different, a macrodomain of nonstructural protein 3 (nsp3). Although 26% of the amino acids in this SARS-CoV-2 macrodomain differ from those seen in other coronaviruses, biochemical and structural data reveal that the protein retains the ability to bind ADP-ribose, which is an important characteristic of beta coronaviruses, and potential therapeutic target.

biochemistry↗