1. Modeling of solvent role in protein folding experiments : dissertationKnarik Yeritsyan, 2025, doctoral dissertation Abstract: The Zimm-Bragg (ZB) model serves as a fundamental framework for elucidating conformational transitions in biopolymers, offering simplicity and efficacy in processing experimental data. This study provides a comprehensive review of the Zimm-Bragg model and its Hamiltonian formulation, with particular emphasis on incorporating water interactions and chain size effects into the computational framework. We propose a modified ZB model that accounts for water-polypeptide interactions, demonstrating its ability to describe phenomena such as cold denaturation and helix-coil transitions. In the realm of NanoBioTechnologies, the manipulation of short polypeptide chains is commonplace. Experimental investigation of these chains in vitro often relies on techniques like Circular Dichroism (CD) and timeresolved infrared spectroscopy. Determining interaction parameters necessitates processing the temperature dependence of the normalized degree of helicity through model fitting. Leveraging recent advancements in the Hamiltonian formulation of the Zimm and Bragg model, we explicitly incorporate chain length and solvent effects into the theoretical description. The resulting expression for helicity degree adeptly fits experimental data, yielding hydrogen bonding energies and nucleation parameter values consistent with field standards. Differential Scanning Calorimetry (DSC) stands as a potent tool for measuring the specific heat profile of materials, including proteins. However, relating the measured profile to microscopic properties requires a suitable model for fitting. We propose a novel algorithm for processing DSC experimental data based on the ZB theory of protein folding in water. This approach complements the classical two-state paradigm and provides insights into protein-water and intraprotein hydrogen bonding energies. An analytical expression for heat capacity, considering water interaction, is derived and successfully applied to fit numerous DSC experimental datasets reported in the literature. Additionally, we compare this approach with the classical two-state model, demonstrating its efficacy in fitting DSC data. Furthermore, we have developed and launched a free online tool for processing CD and DSC experimental data related to protein folding, aiming to support scientific research.
Keywords: Zimm-Bragg model, conformational transitions, helix-coil transitions, cold denaturation, circular dichroism, differential scanning calorimetry, protein folding, water-protein interaction, hydrogen bonding energy, degree of helicity, short polypeptide chains, protein heat capacity, protein data analysis, dissertations
Published in RUNG: 27.01.2025; Views: 567; Downloads: 11
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2. The second knee in the cosmic ray spectrum observed with the surface detector of the Pierre Auger ObservatoryGabriel Brichetto Orquera, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution Abstract: The determination of the energy spectrum features with low systematic uncertainty is crucial for interpreting the nature of cosmic rays. In this study, we conducted a measurement of the energy spectrum at the Pierre Auger Observatory using a surface detector with a calorimetric
energy scale indirectly set by a fluorescence detector. The surface detector consists of an array of water-Cherenkov detectors that extends over 3000 km^2 with 1500m spacing. Additionally,
two nested arrays of the same kind with 750m and 433m spacing were utilized to lower the energy threshold of the measurements. This contribution presents, for the first time, the spectrum measured with the 433m array, which reduces the energy threshold down to 63 PeV, nearly half the energy at which we previously published a steepening using the 750m array. Our measurements include a characterization of the spectral features of the flux steepening around 230 PeV, known
as the second-knee. The study benefits from a nearly 100% duty cycle and geometrical exposure. Notably, this is the first simultaneous measurement of the second knee energy and spectral indexes before and after the break, using a surface detector with an energy scale predominantly independent of air shower simulations and assumptions regarding hadronic interaction models.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, hadronic interaction model, water-Cherenkov detectors
Published in RUNG: 23.01.2024; Views: 1844; Downloads: 5
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3. Modelling water for calorimetry of proteinsKnarik Yeritsyan, Artem Badasyan, 2023, published scientific conference contribution abstract Abstract: Differential Scanning Calorimetry (DSC) is a powerful technique used to study the thermal stability and unfolding of proteins. DSC provides the excess heat capacity profile and is used to study the thermodynamics of a given protein. By fitting DSC data to the model, researchers can obtain valuable information about the thermodynamics of protein folding and unfolding, which can help them better understand protein structure, stability, and function.
Based on Hamiltonian representation of ZB model and using the solvent effects we derived an expression for heat capacity in proteins and successfuly fit it to experimental data. As we show, our model provides a better fit to experimental data, as compared to the 2-state model. The model we propose takes into account also water effects and we show that it fits better to experimental data giving inter- and intra-molecular H-bonding energies instead of reporting only one total enthalpy.
Keywords: Zimm-Bragg model, water model, helix-coil transition, protein folding, differential scanning calorimetry
Published in RUNG: 18.10.2023; Views: 2620; Downloads: 0
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4. Spin model of water and post-processing of protein folding experimentsArtem Badasyan, Knarik Yeritsyan, 2023, published scientific conference contribution abstract Abstract: The presence of several distinct minima in nearest-neighbor potentials in polymers makes it possible
to describe polymer conformations in terms of discrete isomeric states, naturally leading to spin
language. Using this general approach, a decade ago we have suggested the Hamiltonian formulation
for the Zimm and Bragg model of protein conformations [1,2]. Later we have augmented the model
by an oversimplified spin model for water, resulting in both cold and hot denaturations [3]. We
construct the Statistical Mechanics for the model and get access to its Thermodynamics. Resulting
order parameter and specific heat expressions are successfully fit to available experimental data [4].
Thanks to solid and traceable theoretical foundations, the procedure provides better quality fits as
compared to the state-of-the-art two-state model, routinely used to process protein folding
experiments.
Keywords: spin model, water, protein folding
Published in RUNG: 04.09.2023; Views: 2266; Downloads: 7
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6. Implicit water model within the Zimm-Bragg approach to analyze experimental data for heat and cold denaturation of proteinsArtem Badasyan, Sh. A. Tonoyan, Matjaž Valant, Jože Grdadolnik, 2021, original scientific article Abstract: Studies of biopolymer conformations essentially rely on theoretical models that are routinely
used to process and analyze experimental data. While modern experiments allow study of
single molecules in vivo, corresponding theories date back to the early 1950s and require an
essential update to include the recent significant progress in the description of water. The
Hamiltonian formulation of the Zimm-Bragg model we propose includes a simplified, yet
explicit model of water-polypeptide interactions that transforms into the equivalent implicit
description after performing the summation of solvent degrees of freedom in the partition
function. Here we show that our model fits very well to the circular dichroism experimental
data for both heat and cold denaturation and provides the energies of inter- and intra-
molecular H-bonds, unavailable with other processing methods. The revealed delicate
balance between these energies determines the conditions for the existence of cold dena-
turation and thus clarifies its absence in some proteins.
Keywords: protein folding, cold denaturation, water, Zimm-Bragg model
Published in RUNG: 06.05.2021; Views: 3421; Downloads: 17
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