Nonlocal Singular Problems and Applications to MEMS

We consider fourth order nonlinear problems which describe electrostatic actuation in MicroElectroMechanicalSystems (MEMS) both in the stationary case and in the evolution case; we prove existence, uniqueness and regularity theorems by exploiting the Near Operators Theory

Cooperative binding of the cationic porphyrin tris-t4 enhances catalytic activity of 20s proteasome unveiling a complex distribution of functional states

The present study provides new evidence that cationic porphyrins may be considered as tunable platforms to interfere with the structural “key code” present on the 20S proteasome α-rings and, by consequence, with its catalytic activity. Here, we describe the functional and conformational effects on the 20S proteasome induced by the cooperative binding of the tri-cationic 5-(phenyl)-10,15,20-(tri N-methyl-4-pyridyl) porphyrin (Tris-T4). Our integrated kinetic, NMR, and in silico analysis allowed us to disclose a complex effect on the 20S catalytic activity depending on substrate/porphyrin concentration. The analysis of the kinetic data shows that Tris-T4 shifts the relative populations of the multiple interconverting 20S proteasome conformations leading to an increase in substrate hydrolysis by an allosteric pathway. Based on our Tris-T4/h20S interaction model, Tris-T4 is able to affect gating dynamics and substrate hydrolysis by binding to an array of negatively charged and hydrophobic residues present on the protein surface involved in the 20S molecular activation by the regulatory proteins (RPs). Accordingly, despite the fact that Tris-T4 also binds to the α3ΔN mutant, allosteric modulation is not observed since the molecular mechanism connecting gate dynamics with substrate hydrolysis is impaired. We envisage that the dynamic view of the 20S conformational equilibria, activated through cooperative Tris-T4 binding, may work as a simplified model for a better understanding of the intricate network of 20S conformational/functional states that may be mobilized by exogenous ligands, paving the way for the development of a new generation of proteasome allosteric modulators

Electronic Circular Dichroism Detects Conformational Changes Associated with Proteasome Gating Confirmed Using AFM Imaging

Many chronic diseases, including cancer and neurodegeneration, are linked to proteasome dysregulation. Proteasome activity, essential for maintaining proteostasis in a cell, is controlled by the gating mechanism and its underlying conformational transitions. Thus, developing effective methods to detect gate-related specific proteasome conformations could be a significant contribution to rational drug design. Since the structural analysis suggests that gate opening is associated with a decrease in the content of α-helices and β-sheets and an increase in random coil structures, we decided to explore the application of electronic circular dichroism (ECD) in the UV region to monitor the proteasome gating. A comparison of ECD spectra of wild type yeast 20S proteasome (predominantly closed) and an open-gate mutant (α3ΔN) revealed an increased intensity in the ECD band at 220 nm, which suggests increased contents of random coil and β-turn structures. This observation was further supported by evaluating ECD spectra of human 20S treated with low concentration of SDS, known as a gate-opening reagent. Next, to evaluate the power of ECD to probe a ligand-induced gate status, we treated the proteasome with H2T4, a tetracationic porphyrin that we showed previously to induce large-scale protein conformational changes upon binding to h20S. H2T4 caused a significant increase in the ECD band at 220 nm, interpreted as an induced opening of the 20S gate. In parallel, we imaged the gate-harboring alpha ring of the 20S with AFM, a technique that we used previously to visualize the predominantly closed gate in latent human or yeast 20S and the open gate in α3ΔN mutant. The results were convergent with the ECD data and showed a marked decrease in the content of closed-gate conformation in the H2T4-treated h20S. Our findings provide compelling support for the use of ECD measurements to conveniently monitor proteasome conformational changes related to gating phenomena. We predict that the observed association of spectroscopic and structural results will help with efficient design and characterization of exogenous proteasome regulators

Jatrophane diterpenes as modulators of multidrug resistance. Advances of structure-activity relationships and discovery of the potent lead pepluanin A

From the whole plant of Euphorbia peplus L., five new diterpenes based on a jatrophane skeleton (pepluanins A-E, 1-5) were isolated, together with two known analogues (6 and 7), which served to divulge in detail the structure-activity relationships within this class of P-glycoprotein inhibitors. The results revealed the importance of substitutions on the medium-sized ring (carbons 8, 9, 14, and 15). In particular, the activity is collapsed by the presence of a free hydroxyl at C-8, while it increases with a carbonyl at C-14, an acetoxyl at C-9, and a free hydroxyl at C-15. The most potent compound of the series, pepluanin A, showed a very high activity for a jatrophane diterpene, outperforming cyclosporin A by a factor of at least 2 in the inhibition of Pgp-mediated daunomycin transport

Intestinal lymphangiectasia in a 3-month-old girl: A case report of Hennekam syndrome caused by CCBE1 mutation

RATIONAL: Intestinal lymphangiectasia (IL) is a rare disease characterized by dilatation and rupture of intestinal lymphatic channels leading to protein-losing enteropathy. IL is classified as primary and secondary types. PATIENT CONCERNS: A 3-month-old girl born at term from vaginal delivery with an APGAR score of 10/10 and birth weight of 4.310 g (>97° percentile) was admitted to our hospital because of increasing abdominal tenderness and diarrhea. At first examination, she presented an abdominal circumference of 60 cm, edema of the lower extremities and vulva, and facial dysmorphisms (hypertelorism, flat nasal bridge, flat mid-face). DIAGNOSIS: Once admitted, ultrasonography showed a large amount of ascites, while blood laboratory investigations revealed severe hypoproteinemia, hypoalbuminemia and hypogammaglobulinemia. Lymphoscintigraphy with 99m-Tc-nanocolloid demonstrated abnormal leakage of the tracer in the abdomen as evidence of IL. To detect a possible secondary, exams were performed and demonstrated positive antibody titres for CMV-IgM and IgG in blood and CMV-DNA positivity in blood, urine, saliva, maternal milk, and gastric and duodenal biopsies. Genetic investigations identified the genomic variant c.472C>T of the CCBE1 gene, coding for a protein variant (p.Arg158Cys), in homozygosity. INTERVENTIONS: Total parenteral nutrition was started and continued for a total of 18 days, then gradually bridged by enteral nutrition with a special formula. In addition, antiviral therapy for CMV infection was added first with intravenous ganciclovir for 14 days, resulting in the disappearance of blood viral load after 7 days of therapy and then with valganciclovir per os for another 30 days. OUTCOMES: The clinical course of the child gradually improved. A few days after starting treatments, lower extremities and vulvar edema disappeared, and abdominal circumference gradually decreased to a stable value of 38 cm, without any ultrasonographic signs of ascites left. Moreover, serum albumin and IgG rose to normal values after 3 months (4.3 g/dL and 501 mg/dL, respectively). LESSONS: This case suggests that in presence of IL both primary and secondary causes should be evaluated. On the other hand, genetic diagnosis is crucial not only for diagnosis but also for prognosis in HS. Life expectancy and quality could deeply vary among different gene mutations and protein variants of the same gene. Further studies and case reports are needed to better understand the clinical meaning of these genetic results and the role of CMV as trigger of IL

Existence and uniqueness of global solutions to fully nonlinear second order elliptic systems

We consider the problem of existence and uniqueness of strong a.e. solutions u:Rn⟶RNu:Rn⟶RN to the fully nonlinear PDE system F(⋅,D2u)=f, a.e. on Rn,(1) F(⋅,D2u)=f, a.e. on Rn,(1) when f∈L2(Rn)Nf∈L2(Rn)N and F is a Carathéodory map. (1) has not been considered before. The case of bounded domains has been studied by several authors, firstly by Campanato and under Campanato’s ellipticity condition on F. By introducing a new much weaker notion of ellipticity, we prove solvability of (1) in a tailored Sobolev “energy” space and a uniqueness estimate. The proof is based on the solvability of the linearised problem by Fourier transform methods, together with a “perturbation device” which allows to use Campanato’s near operators. We also discuss our hypothesis via counterexamples and give a stability theorem of strong global solutions for systems of the form (1)

Peptide-chelating agent conjugate for selective targeting of somatostatin receptor type1: Synthesis and characterization

Previously reported results suggest that the analogue of the somatostatin des-AA 1,2,5[D-Trp 8,IAmp 9]-somatostatin (CH-275) peptide bearing chelating agents able to coordinate radioactive metals could be used for scintigraphic imaging of tumor lesions overexpressing sstr1. An efficient synthetic procedure for the preparation of the somatostatin analogue CH-275 and its conjugate DTPAGlu-Gly-CH-275, bearing the chelating agent DTPAGlu (DTPAGlu = N,N-bis[2-[bis(carboxy-ethyl)amino]ethyl]-L-glutamic acid) on the N-terminus, by solid-phase peptide synthesis and 9-flourenymethyoxycarbonyl (Fmoc) chemistry, is here reported. Rapid and efficient labeling of DTPAGlu-Gly-CH-275 was achieved by addition of IIIIn(III) to the compound. Typical yields were greater than 97% as determined by reversed phase high performance liquid chromatography (HPLC) at specific activities in the range 4-9 GBq/μmol (100-250 Ci/mmol). A preliminary biological assay of the binding ability of IIIIn-DTPAGlu-Gly-CH-275 indicates, however, that the labeled compound does not display any specific interaction with somatostatin sstrl receptors in the tested cell lines. To confirm this unexpected negative result, competition binding experiments were carried out, in which fixed tracer amounts of the 125!-labeled somatostatin-14 were incubated with the receptor-expressing cells in the presence of DTPAGlu-Gly-CH-275 or CH-275 at concentrations ranging from 10 -10 to 10 -3 M. While CH-275 shows a IC 50 of 80 nM similar to that already found in displacement experiments on CHO-Kl sstrl-transfected cells, DTPAGlu-Gly-CH-275 displays instead very low or negligible affinity towards this receptor. The NMR solution characterization indicates that the presence of DTPAGlu does not influence the conformational and chemical features of the peptide moiety, thus suggesting that the loss in binding activity should be due to steric hindrance of either the chelating agent DTPAGlu or its indium comple

Discovery of a spirocyclic 3-bromo-4,5-dihydroisoxazole covalent inhibitor of hGAPDH with antiproliferative activity against pancreatic cancer cells

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key glycolytic enzyme, plays a crucial role in the energy metabolism of cancer cells and has been proposed as a valuable target for the development of anticancer agents. Among a series of 5-substituted 3-bromo-4,5-dihydroisoxazole (BDHI) derivatives, we identified the spirocyclic compound 11, which is able to covalently inactivate recombinant human GAPDH (hGAPDH) with a faster reactivity than koningic acid, one of the most potent hGAPDH inhibitors known to date. Computational studies confirmed that conformational rigidification is crucial to stabilize the interaction of the inhibitor with the binding site, thus favoring the subsequent covalent bond formation. Investigation of intrinsic warhead reactivity at different pH disclosed the negligible reactivity of 11 with free thiols, highlighting its ability to selectively react with the activated cysteine of hGAPDH with respect to other sulfhydryl groups. Compound 11 strongly reduced cancer cell growth in four different pancreatic cancer cell lines and its antiproliferative activity correlated well with the intracellular inhibition of hGAPDH. Overall, our results qualify 11 as a potent hGAPDH covalent inhibitor with a moderate drug-like reactivity that could be further exploited to develop anticancer agents

Probing the Residual Structure in Avian Prion Hexarepeats by CD, NMR and MD Techniques

Many proteins perform essential biological functions by means of regions that lacking specific organized structure exist as an ensemble of interconverting transient conformers. The characterization of such regions, including the description of their structural propensities, number of conformations and relative populations can provide useful insights. Prion diseases result from the conversion of a normal glycoprotein into a misfolded pathogenic isoform. The structures of mammal and chicken prion proteins show a similar fold with a globular domain and a flexible N-terminal portion that contains different repeated regions: octarepeats (PHGGGWGQ) in mammals and hexarepeats (PHNPGY) in chickens. The higher number of prolines in the hexarepeat region suggests that this region may retain a significant amount of residual secondary structure. Here, we report the CD, NMR and MD characterization of a peptide (2-HexaPY) composed of two hexarepeats. We combine experimental NMR data and MD to investigate at atomic level its ensemble-averaged structural properties, demonstrating how each residue of both repeats has a different quantified PPII propensity that shows a periodicity along the sequence. This feature explains the absence of cooperativity to stabilize a PPII conformation. Nonetheless, such residual structure can play a role in nucleating local structural transitions as well as modulating intra-molecular or inter-molecular interactions

Folding mechanisms steer the amyloid fibril formation propensity of highly homologous proteins

Significant advances in the understanding of the molecular determinants of fibrillogenesis can be expected from comparative studies of the aggregation propensities of proteins with highly homologous structures but different folding pathways. Here, we fully characterize, by means of stopped-flow, T-jump, CD and DSC experiments, the unfolding mechanisms of three highly homologous proteins, zinc binding Ros87 and Ml153-149 and zinc-lacking Ml452-151. The results indicate that the three proteins significantly differ in terms of stability and (un)folding mechanisms. Particularly, Ros87 and Ml153-149 appear to be much more stable to guanidine denaturation and are characterized by folding mechanisms including the presence of an intermediate. On the other hand, metal lacking Ml452-151 folds according to a classic two-state model. Successively, we have monitored the capabilities of Ros87, Ml452-151 and Ml153-149 to form amyloid fibrils under native conditions. Particularly, we show, by CD, fluorescence, DLS, TEM and SEM experiments, that after 168 hours, amyloid formation of Ros87 has started, while Ml153-149 has formed only amorphous aggregates and Ml452-151 is still monomeric in solution. This study shows how metal binding can influence protein folding pathways and thereby control conformational accessibility to aggregation-prone states, which in turn changes aggregation kinetics, shedding light on the role of metal ions in the development of protein deposition diseases