Effects of Random Mutagenesis and In Vivo Selection on the Specificity and Stability of a Thermozyme

Factors that give enzymes stability, activity, and substrate recognition result from the combination of few weak molecular interactions, which can be difficult to study through rational protein engineering approaches. We used irrational random mutagenesis and in vivo selection to test if a β-glycosidase from the thermoacidophile Saccharolobus solfataricus (Ssβ-gly) could complement an Escherichia coli strain unable to grow on lactose. The triple mutant of Ssβ-gly (S26L, P171L, and A235V) was more active than the wild type at 85 °C, inactivated at this temperature almost 300-fold quicker, and showed a 2-fold higher kcat on galactosides. The three mutations, which were far from the active site, were analyzed to test their effect at the structural level. Improved activity on galactosides was induced by the mutations. The S26L and P171L mutations destabilized the enzyme through the removal of a hydrogen bond and increased flexibility of the peptide backbone, respectively. However, the flexibility added by S26L mutation improved the activity at T > 60 °C. This study shows that random mutagenesis and biological selection allowed the identification of residues that are critical in determining thermal activity, stability, and substrate recognitio

Obstetric and neonatal outcomes after SARS-CoV-2 infection in the first trimester of pregnancy: A prospective comparative study

OBJECTIVE(S): This prospective observational cohort study aimed to evaluate whether women with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection during the first trimester of pregnancy are at higher risk of adverse obstetric and neonatal outcomes compared to negative patients. STUDY DESIGN: Seromolecular testing for SARS‐CoV‐2 was performed at 12, 16, 21 weeks, and at delivery; the cohort was then subdivided into a first‐trimester SARS‐CoV‐2‐positive (case) group and a SARS‐CoV‐2‐negative (control) group. The primary outcome was a composite adverse obstetric outcome, defined as the presence of either abortion, preterm delivery, preterm prelabor rupture of membranes, preeclampsia, intrauterine growth restriction, stillbirth; and a composite measure of adverse neonatal events, including either 1‐ and 5‐min Apgar score ≤ 7, neonatal intensive care unit admission and congenital birth defects. Maternal symptoms and antibody titer were secondarily assessed. RESULTS: A total of 17 of 164 women tested positive for SARS‐CoV‐2 (10.3%) in the first trimester. One SARS‐CoV‐2‐positive patient who gave birth at another hospital was excluded. Composite adverse obstetric outcome was observed in 6.2% (1/16) SARS‐CoV‐2‐positive and 10.5% (11/105) SARS‐CoV‐2‐negative women; composite adverse neonatal outcome in 12.5% (2/16) and 7.6% (8/105), respectively. In the newborns of women who had developed IgG antibodies, the same antibodies were detected in arterial cord blood and the nasopharyngeal swab tested negative for SARS‐CoV‐2. No maternal pneumonia or hospital admission due to coronavirus disease‐19 were recorded. CONCLUSION: Asymptomatic or mildly symptomatic women during the first trimester of pregnancy did not experience significantly more adverse events than SARS‐CoV‐2‐negative women

Probing the catalytically essential residues of the alpha-L-fucosidase from the hyperthermophilic archaeon Sulfolobus solfataricus

Retaining glycosidases promote the hydrolysis of the substrate by following a double-displacement mechanism involving a covalent intermediate. The catalytic residues are a general acid/base catalyst and the nucleophile. Experimental identification of these residues in a specific glycosidase allows for the assigning of the corresponding residues in all of the other enzymes belonging to the same family. By means of sequence alignment, mutagenesis, and detailed kinetic studies of the alpha-fucosidase from Sulfolobus solfataricus (Ssalpha-fuc) (family 29), we show here that the residues, invariant in this family, have the function inferred from the analysis of the 3D structure of the enzyme from Thermotoga maritima (Tmalpha-fuc). These include in Ssalpha-fuc the substrate-binding residues His46 and His123 and the nucleophile of the reaction, previously described. The acid/base catalyst could be assigned less easily. The k(cat) of the Ssalpha-fucGlu292Gly mutant, corresponding to the acid/base catalyst of Tmalpha-fuc, is reduced by 154-fold but could not be chemically rescued. Instead, the Ssalpha-fucGlu58Gly mutant revealed a 4000-fold reduction of k(cat)/K(M) if compared to the wild-type and showed the rescue of the k(cat) by sodium azide at wild-type levels. Thus, our data suggest that a catalytic triad, namely, Glu58, Glu292, and Asp242, is involved in catalysis. Glu58 and Glu292 cooperate in the role of acid/base catalyst, while Asp242 is the nucleophile of the reaction. Our data suggest that in glycosidase family 29 alpha-fucosidases promoting the retaining mechanism with slightly different catalytic machineries coexist

Probing the role of an invariant active site His in family GH1 β-glycosidases

The reaction mechanism of glycoside hydrolases belonging to family 1 (GH1) of carbohydrate-active enzymes classification, hydrolysing β-O-glycosidic bonds, is well characterised. This family includes several thousands of enzymes with more than 20 different EC numbers depending on the sugar glycone recognised as substrate. Most GH1 β-glycosidases bind their substrates with similar specificity through invariant amino acid residues. Despite extensive studies, the clear identification of the roles played by each of these residues in the recognition of different glycones is not always possible. We demonstrated here that a histidine residue, completely conserved in the active site of the enzymes of this family, interacts with the C2-OH of the substrate in addition to the C3-OH as previously shown by 3 D-structure determination

Applications in Biocatalysis of Glycosyl Hydrolases from the Hyperthermophilic Archaeon Sulfolobus solfataricus

Carbohydrates serve as structural components and en- ergy sources of cells. More interestingly, however, these biomolecules are involved in a variety of molecular recognition processes in intercellular communication and signal transduction such as cell adhesion, differ- entiation, development and regulation. For these rea- sons, great interest has arisen in carbohydrate-based pharmaceuticals and on the development of techniques for the analysis and synthesis of oligosaccharides. In this respect, enzymes involved in carbohydrates hydrolysis and modification are increasingly being utilised for the bioconversion of sugars, for the synthesis of oligosac- charides with potential application, and for the charac- terisation of carbohydrate compounds of unknown structure. In this review, the enzymology and the applications of three glycosyl hydrolases from the archaeon Sulfolobus solfataricus are described. In particular, we focus on the enzymological properties of a b-glycosidase, an a-xylo- sidase, and an a-fucosidase; their exploitation in oligo- saccharides synthesis will be also described

Structural characterization of the nonameric assembly of an Archaeal alpha-L-fucosidase by synchrotron small angle X-ray scattering

alpha-l-Fucosidase is a lysosomal enzyme responsible for hydrolyzing the alpha-1,6-linked fucose joined to the reducing-end N-acetylglucosamine of carbohydrate moieties in glycoproteins. The first alpha-l-fucosidase from Archaea was recently identified in the genome of the hyperthermophile Sulfolobus solfataricus; the enzyme is encoded by two open reading frames separated by a -1 frameshift. A preliminary biochemical and biophysical characterization of this extremophile enzyme has been carried out both in solution, through small angle X-ray scattering experiments, and in the crystalline state, showing an unusual oligomeric assembly resulting from the association of nine subunits, endowed with 3-fold molecular symmetry

Functional interaction between p75(NTR) and TrkA: the endocytic trafficking of p75(NTR) is driven by TrkA and regulates TrkA-mediated signalling

The topology and trafficking of receptors play a key role in their signalling capability. Indeed, receptor function is related to the microenvironment inside the cell, where specific signalling molecules are compartmentalized. The response to NGF (nerve growth factor) is strongly dependent on the trafficking of its receptor, TrkA. However, information is still scarce about the role of the cellular localization of the TrkA co-receptor, p75(NTR) (where NTR is neurotrophin receptor), following stimulation by NGF. It has been shown that these two receptors play a key role in epithelial tissue and in epithelial-derived tumours, where the microenvironment at the plasma membrane is defined by the presence of tight junctions. Indeed, in thyroid carcinomas, rearrangements of TrkA are frequently found, which produce TrkA mutants that are localized exclusively in the cytoplasm. We used a thyroid cellular model in which it was possible to dissect the trafficking of the two NGF receptors upon neurotrophin stimulation. In FRT (Fischer rat thyroid) cells, endogenous TrkA is localized exclusively on the basolateral surface, while transfected p75(NTR) is selectively distributed on the apical membrane. This cellular system enabled us to selectively stimulate either p75(NTR) or TrkA and to analyse the role of receptor trafficking in their signalling capability. We found that, after binding to NGF, p75(NTR) was co-immunoprecipitated with TrkA and was transcytosed at the basolateral membrane. We showed that the TrkA–p75(NTR) interaction is necessary for this relocation of p75(NTR) to the basolateral side. Interestingly, TrkA-specific stimulation by basolateral NGF loading also induced the TrkA–p75(NTR) interaction and subsequent p75(NTR) transcytosis at the basolateral surface. Moreover, specific stimulation of p75(NTR) by NGF activated TrkA and the MAPK (mitogen-activated protein kinase) pathway. Our data indicate that TrkA regulates the subcellular localization of p75(NTR) upon stimulation with neurotrophins, thus affecting the topology of the signal transduction molecules, driving the activation of a specific signal transduction pathway