Investigations into Protein Structure

A special issue of Biophysica (ISSN 2673-4125).

Deadline for manuscript submissions: 28 February 2026 | Viewed by 1704

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Center for Technological Development in Health (CDTS), National Institute of Science and Technology for Innovation in Neglected Diseases Populations (INCT-IDPN), Oswaldo Cruz Foundation (FIOCRUZ), Rio de Janeiro 21040-900, RJ, Brazil
Interests: vaccines; infectious diseases; molecular immunology; epitopes; neglected diseases; biochemistry; molecular biology; proteins; structure; cell biology
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Special Issue Information

Dear Colleagues,

Proteins, the fundamental components of life, are not just essential to the complex interplay of cellular, physiological, and immunological processes. They are, in fact, the ultimate expression of genetic information, meticulously decoded from DNA. Within the dynamic environment of the cell, proteins perform a wide range of functions, acting as both structural frameworks and catalysts that power biological reactions. A sophisticated code embedded in the four-letter DNA alphabet is central to their versatility. This genetic code, through sequences of amino acids, determines the folding and configuration of proteins into an astounding variety of structures, each uniquely suited to a specific role. From the resilient collagen fibers that provide tissue support to the dynamic molecular motors enabling cellular motion, proteins exemplify the diversity encoded in the genome.

Additionally, proteins orchestrate biochemical reactions and can serve as antigens, sparking targeted immune responses and therapeutic innovations. Their amino acid sequences and specific regions act as catalysts, mediate protein-protein interactions, and drive numerous biological processes that would otherwise proceed sluggishly. Whether functioning as enzymes facilitating nutrient breakdown for energy or as signaling molecules regulating cellular communication, proteins are not just important; they are central to all biological activity. Despite their complexity, proteins arise from a relatively simple genetic blueprint, which can produce an almost limitless array of structures, each optimized for its function. This simplicity amidst complexity highlights the elegance of life’s molecular machinery, driven by proteins’ hierarchical structures. Proteins, from providing structural support to ensuring catalytic efficiency, embody biological systems' adaptability and precision, highlighting life's extraordinary intricacies. This Special Issue aims to gather studies that push the boundaries of our understanding of protein structures, including enzymes, structural proteins, membranes, and other components of living organisms. Contributions related to bioinformatics, methodologies for examining the four structural levels of proteins, SAXS, cryoelectron microscopy, and the interactions between these levels and biochemical and immunological properties, and drug development studies are particularly encouraged. With the wealth of knowledge accumulated over the years, a comprehensive collection of expert articles on this special issue would provide significant value to researchers worldwide.

Dr. Salvatore Giovanni De Simone
Guest Editor

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Keywords

  • protein structure
  • enzymes
  • structural proteins
  • membranes

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Published Papers (4 papers)

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Research

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14 pages, 632 KiB  
Article
Protein Polarimetry, Perfected: Specific Rotation Measurement for the Refracto-Polarimetric Detection of Cryptic Protein Denaturation
by Lisa Riedlsperger, Heinz Anderle, Andreas Schwaighofer and Martin Lemmerer
Biophysica 2025, 5(3), 34; https://doi.org/10.3390/biophysica5030034 - 7 Aug 2025
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Abstract
Protein polarimetry has been evaluated as a simple and straightforward technique to detect the cryptic denaturation of exemplary proteins. The general rules of rotation vs. amino acid and structural composition and the respective knowledge gaps were reviewed, and the specific rotation of cystine [...] Read more.
Protein polarimetry has been evaluated as a simple and straightforward technique to detect the cryptic denaturation of exemplary proteins. The general rules of rotation vs. amino acid and structural composition and the respective knowledge gaps were reviewed, and the specific rotation of cystine was determined in 4 M NaCl solution as [α]D20 = –302.5°. The specific rotations at 589 nm and 436 nm and the ratio were measured for several model proteins, some purified plasma-derived proteins and for three monoclonal antibodies. The immunoglobulin G concentrates all showed a narrow ratio range likely characteristic for this protein class. Heat denaturation experiments were conducted at temperatures between 50 and 85 °C both for short-time (10 min) and for prolonged periods of heat exposure (up to 210 min). Denaturation by heat resulted not only in the known levorotatory shift, but also in a shift in the specific rotation ratio. The stabilizing effect of fatty acids in bovine serum could be demonstrated by this parameter. Polarimetry thus appears to be a particularly sensitive and simple method for the characterization of the identity and the thermal stability of proteins and should therefore be added again as a complimentary method to the toolbox of protein chemistry. Full article
(This article belongs to the Special Issue Investigations into Protein Structure)
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17 pages, 8708 KiB  
Article
Optimizing Single-Particle Analysis Workflow: Comparative Analysis of the Symmetry Parameter and Particle Quantity upon Reconstruction of the Molecular Complex
by Myeong Seon Jeong, Han-ul Kim, Mi Young An, Yoon Ho Park, Sun Hee Park, Sang J. Chung, Yoon-Sun Yi, Sangmi Jun, Young Kwan Kim and Hyun Suk Jung
Biophysica 2025, 5(3), 30; https://doi.org/10.3390/biophysica5030030 - 22 Jul 2025
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Abstract
Recent major advancements in cryo-electron microscopy (cryo-EM) have enabled high-resolution structural analysis, accompanied by developments in image processing software packages for single-particle analysis (SPA). SPA facilitates the 3D reconstruction of proteins and macromolecular complexes from numerous individual particles. In this study, we systematically [...] Read more.
Recent major advancements in cryo-electron microscopy (cryo-EM) have enabled high-resolution structural analysis, accompanied by developments in image processing software packages for single-particle analysis (SPA). SPA facilitates the 3D reconstruction of proteins and macromolecular complexes from numerous individual particles. In this study, we systematically evaluated the impact of symmetry parameters and particle quantity on the 3D reconstruction efficiency using the dihydrolipoyl acetyltransferase (E2) inner core of the pyruvate dehydrogenase complex (PDC). We specifically examined how inappropriate symmetry constraints can introduce structural artifacts and distortions, underscoring the necessity for accurate symmetry determination through rigorous validation methods such as directional Fourier shell correlation (FSC) and local-resolution mapping. Additionally, our analysis demonstrates that efficient reconstructions can be achieved with a moderate particle number, significantly reducing computational costs without compromising structural accuracy. We further contextualize these results by discussing recent developments in SPA workflows and hardware optimization, highlighting their roles in enhancing reconstruction accuracy and computational efficiency. Overall, our comprehensive benchmarking provides strategic insights that will facilitate the optimization of SPA experiments, particularly in resource-limited settings, and offers practical guidelines for accurately determining symmetry and particle quantity during cryo-EM data processing. Full article
(This article belongs to the Special Issue Investigations into Protein Structure)
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14 pages, 2559 KiB  
Article
Insights into Cysteine Protease Complexes with Grafted Chitosan–Poly(N-vinylpyrrolidone) Copolymers: Catalytic Activity and Storage Stability
by Maria S. Lavlinskaya, Andrey V. Sorokin, Anastasia N. Dubovitskaya, Anastasia I. Yutkina, Maxim S. Kondratyev, Marina G. Holyavka, Yuriy F. Zuev and Valeriy G. Artyukhov
Biophysica 2025, 5(2), 18; https://doi.org/10.3390/biophysica5020018 - 8 May 2025
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Abstract
The investigation of structure–function relationships in enzyme polysaccharide complexes provides a theoretical foundation for modulating enzyme properties and expanding their industrial applications. In this study, the interaction of cysteine proteases—bromelain, ficin, and papain—with a grafted chitosan–poly(N-vinylpyrrolidone) copolymers, Cs-g-PVP, was [...] Read more.
The investigation of structure–function relationships in enzyme polysaccharide complexes provides a theoretical foundation for modulating enzyme properties and expanding their industrial applications. In this study, the interaction of cysteine proteases—bromelain, ficin, and papain—with a grafted chitosan–poly(N-vinylpyrrolidone) copolymers, Cs-g-PVP, was examined, and its effect on the catalytic and stability properties of the enzymes was assessed. Molecular docking and Fourier-transform infrared spectroscopy were used to analyze the topology of the resulting complexes and identify macromolecular fragments involved in binding. Based on the obtained results, it was hypothesized that complex formation would lead to a slight reduction in the catalytic activity of cysteine proteases. In vitro studies of the complexes confirmed this hypothesis, showing that the enzymes retained more than 63% of their proteolytic activity while their half-inactivation time during storage increased by up to ~12-fold. The investigated Cs-g-PVP copolymers demonstrated high efficiency as supports for the studied enzymes, capable of retaining up to 100% of the added enzymes. Full article
(This article belongs to the Special Issue Investigations into Protein Structure)
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Review

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20 pages, 3040 KiB  
Review
Quantitative Characterization of Nonspecific Interactions Between Macromolecules in Complex Media: Comparison of Experiment, Theory, and Simulation
by Allen P. Minton
Biophysica 2025, 5(3), 25; https://doi.org/10.3390/biophysica5030025 - 24 Jun 2025
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Abstract
A brief summary of the effect of nonspecific interactions upon chemical equilibria in solutions containing a high total concentration of macromolecular solutes comparable to that found in biological fluid media is presented. Analyses of experimental measurements permitting relatively direct quantitation of the free [...] Read more.
A brief summary of the effect of nonspecific interactions upon chemical equilibria in solutions containing a high total concentration of macromolecular solutes comparable to that found in biological fluid media is presented. Analyses of experimental measurements permitting relatively direct quantitation of the free energy of nonspecific intermolecular interaction in solutions of one or two macrosolutes are described, and a table listing published experimental studies of both homo- and hetero-interactions is provided. Methods for calculating the free energy of nonspecific interaction via theory and computer simulation are described. Recommendations for further progress in both measurement and calculation of interaction free energies are presented. Full article
(This article belongs to the Special Issue Investigations into Protein Structure)
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