- Polska, Kujawsko-Pomorskie, Poland
Adam Liwo
Gdansk University of Technology, Chemistry, Faculty Member
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Anthracycline derivatives, which constitute an important class of antitumor drugs, exhibit undesirable cardiotoxicity owing to their mediation in the process of oxygen reduction to the superoxide anion radical. Earlier work showed that... more
Anthracycline derivatives, which constitute an important class of antitumor drugs, exhibit undesirable cardiotoxicity owing to their mediation in the process of oxygen reduction to the superoxide anion radical. Earlier work showed that this mediation could be facilitated by the formation of complexes with the 1 delta g oxygen molecule prior to reduction. In this paper, we investigate the energetics of the possible peroxides formed by a series of model anthraquinones: 1,4-dihydroxyl- (quinizarin), 1,8-dihydroxyl-, 1-hydroxy-8-methoxy-, 1,8-dimethoxy-, 1,4,5-trimethoxy- and 1,4-dihydroxy-5-methoxy-9,10-anthracenedione, as well as of daunorubicin and demethoxydaunorubicin, by semi-empirical quantum-mechanical MNDO and PM3 methods, and limited STO-3G ab initio calculations. It was found that the oxygen-binding site is determined by three factors: the high electron density and high HOMO coefficients on the carbon atoms to which oxygen binds, the minimum loss of conjugation within the anthraquinone moiety on oxygen binding and the minimum number of bonds to other heavy atoms of the oxygen-binding carbons (the steric effect). For different molecules, the energy of the most stable oxygen complex is the greatest for compounds with the lowest ionization potential. On the basis of this and our earlier studies, it was concluded that the anthracycline derivatives with reduced ability to bind oxygen and, therefore, reduced cardiotoxicity, should possess a high symmetry of II-electron density distribution, a high ionization potential and have all of the oxygen-binding sites condensed to other rings or substituted by bulky groups.
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Research Interests: Engineering, Chemistry, Water, Molecular Dynamics Simulation, Protein Folding, and 15 moreMedicine, Molecular Dynamics, Physical sciences, Proteins, Free Energy, CHEMICAL SCIENCES, Amino Acids, Theoretical Models, Lysine, Arginine, Side-chain, Umbrella Sampling, Glutamic Acid, Potential of Mean Force, and Interaction energy
The secondary structure of proteins results from both local and long-range interactions, the latter being primarily backbone hydrogen bonding. In this chapter, based on our recent work, we suggest that the striking regularity of secondary... more
The secondary structure of proteins results from both local and long-range interactions, the latter being primarily backbone hydrogen bonding. In this chapter, based on our recent work, we suggest that the striking regularity of secondary structure can be described, in a semi-analytical manner, in terms of Kubo cluster cumulants (corresponding to the expansion of the protein's potential of mean force) that originate from the coupling between the backbone-local and backbone-electrostatic interactions. This finding is illustrated by the analysis of the Protein Data Bank statistics. Examples demonstrating the importance of the coupling terms in coarse-grained treatment of proteins are also presented.
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Stabilization of helical conformations of CM15 upon interactions with suramin.
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Highlights • The syndecan ectodomains are flexible random-coil intrinsically disordered proteins.• Their extended conformations have the same size as their cell surface partners.• Their binding-motifs to cells and receptors are not... more
Highlights • The syndecan ectodomains are flexible random-coil intrinsically disordered proteins.• Their extended conformations have the same size as their cell surface partners.• Their binding-motifs to cells and receptors are not accessible in all conformations.• Only some of conformations of the ectodomains may be biologically active.• The syndecan-4 ectodomain forms a disulfide-bonded dimer with extended conformations.
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Abstract: The UNited RESidue (UNRES) force field has been developed for over two decades. This force field has been derived carefully as a potential of mean force of the system studied, which is further expressed in terms of the Kubo... more
Abstract: The UNited RESidue (UNRES) force field has been developed for over two decades. This force field has been derived carefully as a potential of mean force of the system studied, which is further expressed in terms of the Kubo cluster-cumulant functions. New terms in the energy function to improve loop structures have been introduced recently. On the other hand, new concept was developed, in which wave-analysis physics is applied to the protein folding problem. At present, the energy function is based on the Landau Hamiltonian, the minima of which are stable conformations of protein fragments; these minima are obtained as kink solutions of the Discrete Nonlinear Schrodinger Equation. The parameters of the Hamiltonian have been obtained by statistical analysis of known protein structures. The unique feature of this approach is that the curvature description is sufficient for protein folding without any long-distance interactions other than the excluded-volume interactions. The combination of those two methodologies - molecular dynamics with the use of physics-base UNRES force field and the kink approach have been applied to study the flexibility and movement of the kinks as well as their formation and disappearance in the folding process.
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We report major algorithmic improvements of the UNRES package for physics‐based coarse‐grained simulations of proteins. These include (i) introduction of interaction lists to optimize computations, (ii) transforming the inertia matrix to... more
We report major algorithmic improvements of the UNRES package for physics‐based coarse‐grained simulations of proteins. These include (i) introduction of interaction lists to optimize computations, (ii) transforming the inertia matrix to a pentadiagonal form to reduce computing and memory requirements, (iii) removing explicit angles and dihedral angles from energy expressions and recoding the most time‐consuming energy/force terms to minimize the number of operations and to improve numerical stability, (iv) using OpenMP to parallelize those sections of the code for which distributed‐memory parallelization involves unfavorable computing/communication time ratio, and (v) careful memory management to minimize simultaneous access of distant memory sections. The new code enables us to run molecular dynamics simulations of protein systems with size exceeding 100,000 amino‐acid residues, reaching over 1 ns/day (1 μs/day in all‐atom timescale) with 24 cores for proteins of this size. Parallel performance of the code and comparison of its performance with that of AMBER, GROMACS and MARTINI 3 is presented.
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A physics-based model is proposed to derive approximate analytical expressions for the cavity component of the free energy of hydrophobic association of spherical and spheroidal solutes in water. The model is based on the difference... more
A physics-based model is proposed to derive approximate analytical expressions for the cavity component of the free energy of hydrophobic association of spherical and spheroidal solutes in water. The model is based on the difference between the number and context of the water molecules in the hydration sphere of a hydrophobic dimer and of two isolated hydrophobic solutes. It is assumed that the water molecules touching the convex part of the molecular surface of the dimer and those in the hydration spheres of the monomers contribute equally to the free energy of solvation, and those touching the saddle part of the molecular surface of the dimer result in a more pronounced increase in free energy because of their more restricted mobility (entropy loss) and fewer favorable electrostatic interactions with other water molecules. The density of water in the hydration sphere around a single solute particle is approximated by the derivative of a Gaussian centered on the solute molecule with respect to its standard deviation. On the basis of this approximation, the number of water molecules in different parts of the hydration sphere of the dimer is expressed in terms of the first and the second mixed derivatives of the two Gaussians centered on the first and second solute molecules, respectively, with respect to the standard deviations of these Gaussians, and plausible analytical expressions for the cavity component of the hydrophobic-association energy of spherical and spheroidal solutes are introduced. As opposed to earlier hydration-shell models, our expressions reproduce the desolvation maxima in the potentials of mean force of pairs of nonpolar solutes in water, and their advantage over the models based on molecular-surface area is that they have continuous gradients in the coordinates of solute centers.
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By analyzing the Kubo-cluster-cumulant expansion of the potential of mean force of polypeptide chains corresponding to backbone-local interactions averaged over the rotation of the peptide groups about the Cα···Cα virtual bonds, we... more
By analyzing the Kubo-cluster-cumulant expansion of the potential of mean force of polypeptide chains corresponding to backbone-local interactions averaged over the rotation of the peptide groups about the Cα···Cα virtual bonds, we identified two important kinds of “along-chain” correlations that pertain to extended chain segments bordered by turns (usually the β-strands) and to the folded spring-like segments (usually α-helices), respectively, and are expressed as multitorsional potentials. These terms affect the positioning of structural elements with respect to each other and, consequently, contribute to determining their packing. Additionally, for extended chain segments, the correlation terms contribute to propagating the conformational change at one end to the other end, which is characteristic of allosteric interactions. We confirmed both findings by statistical analysis of the virtual-bond geometry of 77 950 proteins. Augmenting coarse-grained and, possibly, all-atom force fields with these correlation terms could improve their capacity to model protein structure and dynamics.
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Contact‐assisted simulations, the contacts being predicted or determined experimentally, have become very important in the determination of the structures of proteins and other biological macromolecules. In this work, the effect of... more
Contact‐assisted simulations, the contacts being predicted or determined experimentally, have become very important in the determination of the structures of proteins and other biological macromolecules. In this work, the effect of contact‐distance restraints on the simulated structures was investigated with the use of multiplexed replica exchange simulations with the coarse‐grained UNRES force field. A modified bounded flat‐bottom restraint function that does not generate a gradient when a restraint cannot be satisfied was implemented. Calculations were run with (i) a set of four small proteins, with contact restraints derived from experimental structures, and (ii) selected CASP11 and CASP12 targets, with restraints as used at prediction time. The bounded penalty function largely omitted false contacts, which were usually inconsistent. It was found that at least 20% of correct contacts must be present in the restraint set to improve model quality with respect to unrestrained simula...
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In this paper we report the improvements and extensions of the UNRES server (https://unres-server.chem.ug.edu.pl) for physics-based simulations with the coarse-grained UNRES model of polypeptide chains. The improvements include the... more
In this paper we report the improvements and extensions of the UNRES server (https://unres-server.chem.ug.edu.pl) for physics-based simulations with the coarse-grained UNRES model of polypeptide chains. The improvements include the replacement of the old code with the recently optimized one and adding the recent scale-consistent variant of the UNRES force field, which performs better in the modeling of proteins with the β and the α+β structures. The scope of applications of the package was extended to data-assisted simulations with restraints from nuclear magnetic resonance (NMR) and chemical crosslink mass-spectroscopy (XL-MS) measurements. NMR restraints can be input in the NMR Exchange Format (NEF), which has become a standard. Ambiguous NMR restraints are handled without expert intervention owing to a specially designed penalty function. The server can be used to run smaller jobs directly or to prepare input data to run larger production jobs by using standalone installations of...
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In addition to wet laboratory experiments and theory, molecular simulations have emerged as the third methodology for studying molecular systems. Nowadays, they are indispensable for interpreting experimental results and understanding the... more
In addition to wet laboratory experiments and theory, molecular simulations have emerged as the third methodology for studying molecular systems. Nowadays, they are indispensable for interpreting experimental results and understanding the molecular origin of biological processes. In this chapter, the techniques for simulating protein structure, dynamics, and thermodynamics are presented. The force fields used in simulations, both in all-atom and in coarse-grained representations, are discussed in terms of the complication and applicability of the models, including treatment of the solvent and the dependence of the accuracy of the treatment and time/size scale covered by each type of model. An overview of simulation techniques – global optimization of conformational energy, Monte Carlo, and molecular dynamics methods, as well as generalized ensemble methods – is presented in the context of their applications. Finally, use of experimental information, mainly from nuclear magnetic resonance data, in the form of restraints imposed during simulations or filters used to postprocess the results, is discussed.
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The potentials of mean force of homodimers of the molecules modeling hydrophobic amino acid side chains (ethane (for alanine), propane (for proline), isobutane (for valine), isopentane (for leucine and isoleucine), ethylbenzene (for... more
The potentials of mean force of homodimers of the molecules modeling hydrophobic amino acid side chains (ethane (for alanine), propane (for proline), isobutane (for valine), isopentane (for leucine and isoleucine), ethylbenzene (for phenylalanine), and methyl propyl sulfide (for methionine)) were determined by umbrella-sampling molecular dynamics simulations in explicit water as functions of distance and orientation. Analytical expressions consisting of the Gay-Berne term to represent effective van der Waals interactions and the cavity term derived in paper 1 of this series were fitted to the potentials of mean force. The positions and depths of the contact minima and the positions and heights of the desolvation maxima, including their dependence on the orientation of the molecules, were well represented by the analytical expressions for all systems, which justifies use of such potentials in coarse-grain protein-folding simulations.
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reuptake of dopamine (DA), a neurotransmitter responsible for pleasurablefeelings.WorkbyShanet.al.suggeststhattwoDAmoleculesmustbindbeforetransport through DAT can occur, while other research disagrees. For thisreason, the transport... more
reuptake of dopamine (DA), a neurotransmitter responsible for pleasurablefeelings.WorkbyShanet.al.suggeststhattwoDAmoleculesmustbindbeforetransport through DAT can occur, while other research disagrees. For thisreason, the transport mechanism remains ambiguous. Using molecular dy-namicssimulationsandadualbilayersystemwithtwoDATproteins,ourstudymimics physiological conditions at a synapse. One protein began in itsoccluded state, with DA and sodium bound in the S1 binding pocket. In thisposter, we report the results from our simulation in which a single DA dissoci-atedfrom the proteininto the intracellular matrixwithout the need for a secondbound DA. The sodium ions have yet to leave the binding pocket.
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The UNited RESidue (UNRES) force field was tested in the 14th Community Wide Experiment on the Critical Assessment of Techniques for Protein Structure Prediction (CASP14), in which larger oligomeric and multimeric targets were present... more
The UNited RESidue (UNRES) force field was tested in the 14th Community Wide Experiment on the Critical Assessment of Techniques for Protein Structure Prediction (CASP14), in which larger oligomeric and multimeric targets were present compared to previous editions. Three prediction modes were tested (i) ab initio (the UNRES group), (ii) contact-assisted (the UNRES-contact group), and (iii) template-assisted (the UNRES-template group). For most of the targets, the contact restraints were derived from the server models top-ranked by the DeepQA method, while the DNCON2 method was used for 11 targets. Our consensus-fragment procedure was used to run template-assisted predictions. Each group also processed the Nuclear Magnetic Resonance (NMR)- and Small Angle X-Ray Scattering (SAXS)-data assisted targets. The average Global Distance Test Total Score (GDT_TS) of the 'Model 1' predictions were 29.17, 39.32, and 56.37 for the UNRES, UNRES-contact, and UNRES-template predictions, respectively, increasing by 0.53, 2.24, and 3.76, respectively, compared to CASP13. It was also found that the GDT_TS of the UNRES models obtained in ab initio mode and in the contact-assisted mode decreases with the square root of chain length, while the exponent in this relationship is 0.20 for the UNRES-template group models and 0.11 for the best performing AlphaFold2 models, which suggests that incorporation of database information, which stems from protein evolution, brings in long-range correlations, thus enabling the correction of force-field inaccuracies.
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In this chapter the scale-consistent approach to the derivation of coarse-grained force fields developed in our laboratory is presented, in which the effective energy function originates from the potential of mean force of the system... more
In this chapter the scale-consistent approach to the derivation of coarse-grained force fields developed in our laboratory is presented, in which the effective energy function originates from the potential of mean force of the system under consideration and embeds atomistically detailed interactions in the resulting energy terms through use of Kubo's cluster-cumulant expansion, appropriate selection of the major degrees of freedom to be averaged out in the derivation of analytical approximations to the energy terms, and appropriate expression of the interaction energies at the all-atom level in these degrees of freedom. Our approach enables the developers to find correct functional forms of the effective coarse-grained energy terms, without having to import them from all-atom force fields or deriving them on a heuristic basis. In particular, the energy terms derived in such a way exhibit correct dependence on coarse-grained geometry, in particular on site orientation. Moreover, analytical formulas for the multibody (correlation) terms, which appear to be crucial for coarse-grained modeling of many of the regular structures such as, e.g., protein α-helices and β-sheets, can be derived in a systematic way. Implementation of the developed theory to the UNIfied COarse-gRaiNed (UNICORN) model of biological macromolecules, which consists of the UNRES (for proteins), NARES-2P (for nucleic acids), and SUGRES-1P (for polysaccharides) components, and is being developed in our laboratory is described. Successful applications of UNICORN to the prediction of protein structure, simulating the folding and stability of proteins and nucleic acids, and solving biological problems are discussed.
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We present the results for CAPRI Round 50, the fourth joint CASP‐CAPRI protein assembly prediction challenge. The Round comprised a total of twelve targets, including six dimers, three trimers, and three higher‐order oligomers. Four of... more
We present the results for CAPRI Round 50, the fourth joint CASP‐CAPRI protein assembly prediction challenge. The Round comprised a total of twelve targets, including six dimers, three trimers, and three higher‐order oligomers. Four of these were easy targets, for which good structural templates were available either for the full assembly, or for the main interfaces (of the higher‐order oligomers). Eight were difficult targets for which only distantly related templates were found for the individual subunits. Twenty‐five CAPRI groups including eight automatic servers submitted ~1250 models per target. Twenty groups including six servers participated in the CAPRI scoring challenge submitted ~190 models per target. The accuracy of the predicted models was evaluated using the classical CAPRI criteria. The prediction performance was measured by a weighted scoring scheme that takes into account the number of models of acceptable quality or higher submitted by each group as part of their f...
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We present the results for CAPRI Round 46, the third joint CASP‐CAPRI protein assembly prediction challenge. The Round comprised a total of 20 targets including 14 homo‐oligomers and 6 heterocomplexes. Eight of the homo‐oligomer targets... more
We present the results for CAPRI Round 46, the third joint CASP‐CAPRI protein assembly prediction challenge. The Round comprised a total of 20 targets including 14 homo‐oligomers and 6 heterocomplexes. Eight of the homo‐oligomer targets and one heterodimer comprised proteins that could be readily modeled using templates from the Protein Data Bank, often available for the full assembly. The remaining 11 targets comprised 5 homodimers, 3 heterodimers, and two higher‐order assemblies. These were more difficult to model, as their prediction mainly involved “ab‐initio” docking of subunit models derived from distantly related templates. A total of ~30 CAPRI groups, including 9 automatic servers, submitted on average ~2000 models per target. About 17 groups participated in the CAPRI scoring rounds, offered for most targets, submitting ~170 models per target. The prediction performance, measured by the fraction of models of acceptable quality or higher submitted across all predictors groups...
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With the advance of experimental procedures obtaining chemical crosslinking information is becoming a fast and routine practice. Information on crosslinks can greatly enhance the accuracy of protein structure modeling. Here, we review the... more
With the advance of experimental procedures obtaining chemical crosslinking information is becoming a fast and routine practice. Information on crosslinks can greatly enhance the accuracy of protein structure modeling. Here, we review the current state of the art in modeling protein structures with the assistance of experimentally determined chemical crosslinks within the framework of the 13th meeting of Critical Assessment of Structure Prediction approaches. This largest‐to‐date blind assessment reveals benefits of using data assistance in difficult to model protein structure prediction cases. However, in a broader context, it also suggests that with the unprecedented advance in accuracy to predict contacts in recent years, experimental crosslinks will be useful only if their specificity and accuracy further improved and they are better integrated into computational workflows.