Survey of Oral Hygiene Habits and Knowledge among School Children: a cross-sectional study from Italy.

AIM: This study is aimed to investigate the oral hygiene practice, knowledge and attitude of young adults, assessing their awareness about the impact of a certain "risk" behaviour on their oral and dental health. MATERIALS: This is a cross-sectional survey study conducted on 829 students (350 males and 479 females, mean age 13-20 years) attending high school in Milan and surrounding areas. They were asked to complete anonymous questionnaire during the first semester of the 2019-2020 school year, under the supervision of a teacher and/or an assigned interviewer. The questionnaire was created by "Laboratorio Adolescenza", in collaboration with the International Alliance of Responsible Drinking (IARD) Research Institute and the University of Milan. All of the data was compiled into table or graph form and analysed. CONCLUSION: There is a general awareness among Italian school children about the risks of bad oral habits, however, there is a need to improve the oral health knowledge, attitude and practices in the target population with emphasis on improvement of oral hygiene practices.

What is the use of nutraceuticals in dentistry? A scoping review.

OBJECTIVE: Recently, nutraceuticals have been widely explored in many medical fields and their use is also increasing in oral and dental problems. Since the nutraceutical evidence landscape in the literature has not been fully elucidated yet, this review aims to examine the effects of commercially available nutraceuticals and their potential evidence and applications in dentistry. MATERIALS AND METHODS: A scoping review was conducted following the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR)" checklist. The electronic search was performed using PubMed/MEDLINE, EMBASE, the Cochrane Library, and Web of Science on March 2022. The inclusion criteria include humans, clinical trials, randomized controlled trials (RCT), reviews, and systematic reviews published over the last ten years. RESULTS: 18 studies met the eligibility criteria. There were 2 RCTs, 11 systematic reviews, and four narrative reviews. In most studies, the clinical indications were oral leucoplakia, periodontitis, osseointegration of implants, oral mucositis, oral clefts, and oral health. Probiotics, prebiotics, polyunsaturated fatty acids, and vitamins A, B, C, D, and E were the most common nutraceuticals used in dentistry. CONCLUSIONS: Nutraceuticals are foods that, according to the literature, may be useful for preventing and treating dental diseases.

Modeling the allosteric modulation on a G-Protein Coupled Receptor: the case of M2 muscarinic Acetylcholine Receptor in complex with LY211960.

Allosteric modulation is involved in a plethora of diverse protein functions, which are fundamental for cells' life. This phenomenon can be thought as communication between two topographically distinct site of a protein structure. How this communication occurs is still matter of debate. Many different descriptions have been presented so far. Here we consider a specific case where any significant conformational change is involved upon allosteric modulator binding and the phenomenon is depicted as a vibrational energy diffusion process between distant protein regions. We applied this model, by employing computational tools, to the human muscarinic receptor M2, a transmembrane protein G-protein coupled receptor known to undergo allosteric modulation whose recently X-ray structure has been recently resolved both with and without the presence of a particular allosteric modulator. Our calculations, performed on these two receptor structures, suggest that for this case the allosteric modulator modifies the energy current between functionally relevant regions of the protein; this allows to identify the main residues responsible for this modulation. These results contribute to shed light on the molecular basis of allosteric modulation and may help design new allosteric ligands.

Vibrational Energy in Proteins Correlates with Topology.

The exchange of vibrational energy in proteins is crucial for their function. Here, we establish a connection between quantities related to it with geometry-based properties such as the proteins' residues coordination number. This relation is proven by molecular simulation in a neuro-pharmacologically relevant transmembrane receptor. The connection demonstrated here paves the way to studies of protein allostery and conformational changes based solely on protein structure.

Conformational ensemble of human α-synuclein physiological form predicted by molecular simulations.

We perform here enhanced sampling simulations of N-terminally acetylated human α-synuclein, an intrinsically disordered protein involved in Parkinson's disease. The calculations, consistent with experiments, suggest that the post-translational modification leads to the formation of a transient amphipathic α-helix. The latter, absent in the non-physiological form, alters protein dynamics at the N-terminal and intramolecular interactions.

Hydration of chloride anions in the NanC Porin from Escherichia coli: a comparative study by QM/MM and MD simulations.

Chloride anions permeate the bacterial NanC porin in physiological processes. Here we present a DFT-based QM/MM study of this porin in the presence of these anions. Comparison is made with classical MD simulations on the same system. In both QM/MM and classical approaches, the anions are almost entirely solvated by water molecules. However, the average water-Cl(-) distance is significantly larger in the first approach. Polarization effects of protein groups close to Cl(-) anion are sizeable. These effects might modulate the anion-protein electrostatic interactions, which in turn play a central role for selectivity mechanisms of the channel.

Large-scale motions and electrostatic properties of furin and HIV-1 protease.

We present a comparative study between two members of serine and aspartic proteases complexed with a peptide substrate. The same computational setup is used to characterize the structural, electrostatic, and electronic properties for the Michaelis complex of furin, a serine protease, and of the aspartic protease from HIV-1. In both cases plane-wave density functional theory (PW-DFT) and empirical force-field-based molecular dynamics calculations are used. For furin, calculations are extended to the complex with the intermediate of the first step of the reaction. Comparisons are also made with results from recent PW-DFT investigations on both families of enzymes and with the same chemical groups in an aqueous environment. It is found that the substrate carbonyl group is more polarized in the furin complex than in the HIV-1 protease one. A further difference regards the large-scale motions of the complexes as a whole and local conformational fluctuations at the active site. The global and local fluctuations are well coupled for HIV-1 protease but not for furin. Thus, despite some chemical analogies in the first step of the reaction mechanism, furin and HIV-1 protease complexes appear to be characterized by a different interplay of electrostatics and conformational fluctuations.

Protonation state and substrate binding to B2 metallo-beta-lactamase CphA from Aeromonas hydrofila.

The zinc enzymes metallo beta-lactamases counteract the beneficial action of beta-lactam antibiotics against bacterial infections, by hydrolyzing their beta-lactam rings. To understand structure/function relationships on a representative member of this class, the B2 M beta L CphA, we have investigated the H-bond pattern at the Zn enzymatic active site and substrate binding mode by molecular simulation methods. Extensive QM calculations at the DFT-BLYP level on eleven models of the protein active site, along with MD simulations of the protein in aqueous solution, allow us to propose two plausible protonation states for the unbound enzyme, which are probably in equilibrium. Docking procedures along with MD simulations and QM calculations suggest that in the complex between the enzyme and its substrate (biapenem), the latter is stable in only one of the two protonation states, in addition it exhibits two different binding modes, of which only one agrees with previous proposals. In both cases, the substrate is polarized as in aqueous solution. We conclude that addressing mechanistic issues on this class of enzymes requires a careful procedure to assign protonation states and substrate docking modes.

Using metadynamics to understand the mechanism of calmodulin/target recognition at atomic detail.

The ability of calcium-bound calmodulin (CaM) to recognize most of its target peptides is caused by its binding to two hydrophobic residues ('anchors'). In most of the CaM complexes, the anchors pack against the hydrophobic pockets of the CaM domains and are surrounded by fully conserved Met side chains. Here, by using metadynamics simulations, we investigate quantitatively the energetics of the final step of this process using the M13 peptide, which has a high affinity and spans the sequence of the skeletal myosin light chain kinase, an important natural CaM target. We established the accuracy of our calculations by a comparison between calculated and NMR-derived structural and dynamical properties. Our calculations provide novel insights into the mechanism of protein/peptide recognition: we show that the process is associated with a free energy gain similar to that experimentally measured for the CaM complex with the homologous smooth muscle MLCK peptide (Ehrhardt et al., 1995, Biochemistry 34, 2731). We suggest that binding is dominated by the entropic effect, in agreement with previous proposals. Furthermore, we explain the role of conserved methionines by showing that the large flexibility of these side chains is a key feature of the binding mechanism. Finally, we provide a rationale for the experimental observation that in all CaM complexes the C-terminal domain seems to be hierarchically more important in establishing the interaction.

Unwinding the helical linker of calcium-loaded calmodulin: a molecular dynamics study.

The fold of calmodulin (CaM) consists of two globular domains connected by a helical segment (the linker), whose conformational properties play a crucial role for the protein's molecular recognition processes. Here we investigate the structural properties of the linker by performing a 11.5 ns molecular dynamics (MD) simulation of calcium-loaded human CaM in aqueous solution. The calculations are based on the AMBER force field. The calculated S2 order parameters are in good accord with NMR data: The structure of the linker in our simulations is much more flexible than that emerging from the Homo sapiens X-ray structure, consistently with the helix unwinding observed experimentally in solution. This process occurs spontaneously in a nanosecond timescale, as observed also in a very recent simulation based on the GROMOS force field. A detailed description of the mechanism that determines the linker unwinding is provided, in which electrostatic contacts between the two globular domains play a critical role. The orientation of the domains emerging from our MD calculations is consistent both with former X-ray scattering data and a recent NMR work. Based on our findings, a rationale for the experimentally measured entropy cost associated to binding to the protein's cellular partners is also given.

A homology model of the pore region of HCN channels.

HCN channels are activated by membrane hyperpolarization and regulated by cyclic nucleotides, such as cyclic adenosine-mono-phosphate (cAMP). Here we present structural models of the pore region of these channels obtained by using homology modeling and validated against spatial constraints derived from electrophysiological experiments. For the construction of the models we make two major assumptions, justified by electrophysiological observations: i), in the closed state, the topology of the inner pore of HCN channels is similar to that of K(+) channels. In particular, the orientation of the S5 and S6 helices of HCN channels is very similar to that of the corresponding helices of the K(+) KcsA and K(+) KirBac1.1 channels. Thus, we use as templates the x-ray structure of these K(+) channels. ii), In the open state, the S6 helix is bent further than it is in the closed state, as suggested (but not proven) by experimental data. For this reason, the template of the open conformation is the x-ray structure of the MthK channel. The structural models of the closed state turn out to be consistent with all the available electrophysiological data. The model of the open state turned out to be consistent with all the available electrophysiological data in the filter region, including additional experimental data performed in this work. However, it required the introduction of an appropriate, experimentally derived constraint for the S6 helix. Our modeling provides a structural framework for understanding several functional properties of HCN channels: i), the cysteine ring at the inner mouth of the pore may act as a sensor of the intracellular oxidizing/reducing conditions; ii), the bending amplitude of the S6 helix upon gating appears to be significantly smaller than that found in MthK channels; iii), the reduced ionic selectivity of HCN channels, relative to that of K(+) channels, may be caused, at least in part, by the larger flexibility of the inner pore of HCN channels.

Reaction mechanism of caspases: insights from QM/MM Car-Parrinello simulations.

Caspases are fundamental targets for pharmaceutical interventions in a variety of diseases involving disregulated apoptosis. Here, we present a quantum mechanics/molecular mechanics Car-Parrinello study of key steps of the enzymatic reaction for a representative member of this family, caspase-3. The hydrolysis of the acyl-enzyme complex is described at the density functional (BLYP) level of theory while the protein frame and solvent are treated using the GROMOS96 force field. These calculations show that the attack of the hydrolytic water molecule implies an activation free energy of ca. DeltaF(A) approximately equal 19 +/- 4 kcal/mol in good agreement with experimental data and leads to a previously unrecognized gem-diol intermediate that can readily (DeltaF(A) approximately equal 5 +/- 3 kcal/mol) evolve to the enzyme products. Our findings assist in elucidating the striking difference in catalytic activity between caspases and other structurally well-characterized cysteine proteases (papains and cathepsins) and may help design novel transition-state analog inhibitors.

Molecular dynamics studies of caspase-3.

Caspase-3 is a fundamental target for pharmaceutical interventions against a variety of diseases involving disregulated apoptosis. The enzyme is active as a dimer with two symmetry-related active sites, each featuring a Cys-His catalytic dyad and a selectivity loop, which recognizes the characteristic DEVD pattern of the substrate. Here, a molecular dynamics study of the enzyme in complex with two pentapeptide substrates DEVDG is presented, which provides a characterization of the dynamic properties of the active form in aqueous solution. The mobility of the substrate and that of the catalytic residues are rather low indicating a distinct preorganization effect of the Michaelis complex. An essential mode analysis permits us to identify coupled motions between the two monomers. In particular, it is found that the motions of the two active site loops are correlated and tend to steer the substrate toward the reactive center, suggesting that dimerization has a distinct effect on the dynamic properties of the active site regions. The selectivity loop of one monomer turns out to be correlated with the N-terminal region of the p12 subunit of the other monomer, an interaction that is also found to play a fundamental role in the electrostatic stabilization of the quaternary structure. To further characterize the specific influence of dimerization on the enzyme essential motions, a molecular dynamics analysis is also performed on the isolated monomer.

Ab initio molecular dynamics-based assignment of the protonation state of pepstatin A/HIV-1 protease cleavage site.

A recent 13C NMR experiment (Smith et al. Nature Struct. Biol. 1996, 3, 946-950) on the Asp 25-Asp25' dyad in pepstatin A/HIV-1 protease measured two separate resonance lines, which were interpreted as being a singly protonated dyad. We address this issue by performing ab initio molecular dynamics calculations on models for this site accompanied by calculations of 13C NMR chemical shifts and isotopic shifts. We find that already on the picosecond time-scale the model proposed by Smith et al. is not stable and evolves toward a different monoprotonated form whose NMR pattern differs from the experimental one. We suggest, instead, a different protonation state in which both aspartic groups are protonated. Despite the symmetric protonation state, the calculated 13C NMR properties are in good agreement with the experiment. We rationalize this result using a simple valence bond model, which explains the chemical inequality of the two C sites. The model calculations, together with our calculations on the complex, allow also the rationalization of 13C NMR properties on other HIV-1 PR/inhibitor complexes. Both putative binding of the substrate to the free enzyme, which has the dyad singly protonated (Piana, S.; Carloni, P. Proteins: Struct., Funct., Genet. 2000, 39, 26-36), and pepstatin A binding to the diprotonated form are consistent with the inverse solvent isotope effect on the onset of inhibition of pepsin by pepstatin and the kinetic iso-mechanism proposed for aspartic proteases (Cho, T.-K.; Rebholz, K.; Northrop, D.B. Biochemistry 1994, 33, 9637-9642).

Molecular dynamics studies on HIV-1 protease drug resistance and folding pathways.

Drug resistance to HIV-1 protease involves the accumulation of multiple mutations in the protein. We investigate the role of these mutations by using molecular dynamics simulations that exploit the influence of the native-state topology in the folding process. Our calculations show that sites contributing to phenotypic resistance of FDA-approved drugs are among the most sensitive positions for the stability of partially folded states and should play a relevant role in the folding process. Furthermore, associations between amino acid sites mutating under drug treatment are shown to be statistically correlated. The striking correlation between clinical data and our calculations suggest a novel approach to the design of drugs tailored to bind regions crucial not only for protein function, but for folding as well.

Ser133 phosphate-KIX interactions in the CREB-CBP complex: an ab initio molecular dynamics study.

Cyclic AMP response element binding protein (CREB) is involved in activation of transcriptional DNA machinery by binding to the coactivator CREB-binding protein (CBP). The interactions between CREB serine phosphate (pSer133) and specific CBP residues (Tyr658 and Lys662) play a crucial role for the thermodynamic stability of the CREB-CBP complex. Here we use ab initio methods to investigate the dynamics and energetics of a relatively large, fully hydrated model complex representing pSer133 and its counterparts of the CBP domain. The calculations suggest that: (1) key contributions to the stabilization of the complex arise not only from electrostatics (as previously proposed) but also from a previously unrecognized "low-barrier hydrogen bond" between pSer133 and Lys662; (2) hydration plays a crucial role for the stabilization of the phosphate charge; (3) formation of the complex involves a significant degree of reorganization of the electronic charge density.

The rational of catalytic activity of herpes simplex virus thymidine kinase. a combined biochemical and quantum chemical study.

Most antiherpes therapies exploit the large substrate acceptance of herpes simplex virus type 1 thymidine kinase (TK(HSV1)) relative to the human isoenzyme. The enzyme selectively phosphorylates nucleoside analogs that can either inhibit viral DNA polymerase or cause toxic effects when incorporated into viral DNA. To relate structural properties of TK(HSV1) ligands to their chemical reactivity we have carried out ab initio quantum chemistry calculations within the density functional theory framework in combination with biochemical studies. Calculations have focused on a set of ligands carrying a representative set of the large spectrum of sugar-mimicking moieties and for which structural information of the TK(HSV1)-ligand complex is available. The k(cat) values of these ligands have been measured under the same experimental conditions using an UV spectrophotometric assay. The calculations point to the crucial role of electric dipole moment of ligands and its interaction with the negatively charged residue Glu(225). A striking correlation is found between the energetics associated with this interaction and the k(cat) values measured under homogeneous conditions. This finding uncovers a fundamental aspect of the mechanism governing substrate diversity and catalytic turnover and thus represents a significant step toward the rational design of novel and powerful prodrugs for antiviral and TK(HSV1)-linked suicide gene therapies.

Water and potassium dynamics inside the KcsA K(+) channel.

Molecular dynamics simulations and electrostatic modeling are used to investigate structural and dynamical properties of the potassium ions and of water molecules inside the KcsA channel immersed in a membrane-mimetic environment. Two potassium ions, initially located in the selectivity filter binding sites, maintain their position during 2 ns of dynamics. A third potassium ion is very mobile in the water-filled cavity. The protein appears engineered so as to polarize water molecules inside the channel cavity. The resulting water induced dipole and the positively charged potassium ion within the cavity are the key ingredients for stabilizing the two K(+) ions in the binding sites. These two ions experience single file movements upon removal of the potassium in the cavity, confirming the role of the latter in ion transport through the channel.

A comparative study of galactose oxidase and active site analogs based on QM/MM Car-Parrinello simulations.

A parallel study of the radical copper enzyme galactose oxidase (GOase) and a low molecular weight analog of the active site was performed with dynamical density functional and mixed quantum-classical calculations. This combined approach enables a direct comparison of the properties of the biomimetic and the natural systems throughout the course of the catalytic reaction. In both cases, five essential forms of the catalytic cycle have been investigated: the resting state in its semi-reduced (catalytically inactive) and its oxidized (catalytically active) form, A(semi) and A(ox), respectively; a protonated intermediate B; the transition state for the rate-determining hydrogen abstraction step C, and its product D. For A and B the electronic properties of the biomimetic compound are qualitatively very similar to the ones of the natural target. However, in agreement with the experimentally observed difference in catalytic activity, the calculated activation energy for the hydrogen abstraction step is distinctly lower for GOase (16 kcal/mol) than for the mimetic compound (21 kcal/mol). The enzymatic transition state is stabilized by a delocalization of the unpaired spin density over the sulfur-modified equatorial tyrosine Tyr272, an effect that for geometric reasons is essentially absent in the biomimetic compound. Further differences between the mimic and its natural target concern the structure of the product of the abstraction step, which is characterized by a weakly coordinated aldehyde complex for the latter and a tightly bound linear complex for the former.