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Kircheva N, Dobrev S, Petkova V, Yocheva L, Angelova S, Dudev T. In Silico Analysis of the Ga 3+/Fe 3+ Competition for Binding the Iron-Scavenging Siderophores of P. aeruginosa-Implementation of Three Gallium-Based Complexes in the "Trojan Horse" Antibacterial Strategy. Biomolecules 2024; 14:487. [PMID: 38672503 PMCID: PMC11048449 DOI: 10.3390/biom14040487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Revised: 04/11/2024] [Accepted: 04/13/2024] [Indexed: 04/28/2024] Open
Abstract
The emergence of multidrug-resistant (MDR) microorganisms combined with the ever-draining antibiotic pipeline poses a disturbing and immensely growing public health challenge that requires a multidisciplinary approach and the application of novel therapies aimed at unconventional targets and/or applying innovative drug formulations. Hence, bacterial iron acquisition systems and bacterial Fe2+/3+-containing enzymes have been identified as a plausible target of great potential. The intriguing "Trojan horse" approach deprives microorganisms from the essential iron. Recently, gallium's potential in medicine as an iron mimicry species has attracted vast attention. Different Ga3+ formulations exhibit diverse effects upon entering the cell and thus supposedly have multiple targets. The aim of the current study is to specifically distinguish characteristics of great significance in regard to the initial gallium-based complex, allowing the alien cation to effectively compete with the native ferric ion for binding the siderophores pyochelin and pyoverdine secreted by the bacterium P. aeruginosa. Therefore, three gallium-based formulations were taken into consideration: the first-generation gallium nitrate, Ga(NO3)3, metabolized to Ga3+-hydrated forms, the second-generation gallium maltolate (tris(3-hydroxy-2-methyl-4-pyronato)gallium), and the experimentally proven Ga carrier in the bloodstream-the protein transferrin. We employed a reliable in silico approach based on DFT computations in order to understand the underlying biochemical processes that govern the Ga3+/Fe3+ rivalry for binding the two bacterial siderophores.
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Affiliation(s)
- Nikoleta Kircheva
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.); (S.A.)
| | - Stefan Dobrev
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.); (S.A.)
| | - Vladislava Petkova
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.); (S.A.)
| | - Lyubima Yocheva
- Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, 1164 Sofia, Bulgaria;
| | - Silvia Angelova
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.); (S.A.)
- University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria
| | - Todor Dudev
- Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, 1164 Sofia, Bulgaria;
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Kircheva N, Dobrev S, Petkova V, Bakalova S, Kaneti J, Angelova S. Theoretical Assessment of the Ligand/Metal/Quadruplex Recognition in the Non-Canonical Nucleic Acids Structures. Molecules 2023; 28:6109. [PMID: 37630360 PMCID: PMC10459790 DOI: 10.3390/molecules28166109] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/11/2023] [Accepted: 08/14/2023] [Indexed: 08/27/2023] Open
Abstract
Quadruplexes (GQs), peculiar DNA/RNA motifs concentrated in specific genomic regions, play a vital role in biological processes including telomere stability and, hence, represent promising targets for anticancer therapy. GQs are formed by folding guanine-rich sequences into square planar G-tetrads which stack onto one another. Metal cations, most often potassium, further stabilize the architecture by coordinating the lone electron pairs of the O atoms. The presence of additional nucleic acid bases, however, has been recently observed experimentally and contributes substantially to the structural heterogeneity of quadruplexes. Therefore, it is of paramount significance to understand the factors governing the underlying complex processes in these structures. The current study employs DFT calculations to model the interactions between metal cations (K+, Na+, Sr2+) and diverse tetrads composed of a guanine layer in combination with a guanine (G)-, adenine (A)-, cytosine (C)-, thymine (T)-, or uracil (U)-based tetrad layer. Moreover, the addition of 4-(3,4-dihydroisoquinolin-2-yl)-2-(quinolin-2-yl)quinazoline to the modeled quadruplexes as a possible mechanism of its well-exerted antitumor effect is assessed. The calculations imply that the metal cation competition and ligand complexation are influenced by the balance between electronic and implicit/explicit solvation effects, the composition of the tetrad layers, as well as by the solvent exposure to the surrounding environment expressed in terms of different dielectric constant values. The provided results significantly enhance our understanding of quadruplex diversity, ligand recognition, and the underlying mechanisms of stabilization at an atomic level.
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Affiliation(s)
- Nikoleta Kircheva
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.)
| | - Stefan Dobrev
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.)
| | - Vladislava Petkova
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.)
| | - Snezhana Bakalova
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (S.B.); (J.K.)
| | - Jose Kaneti
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (S.B.); (J.K.)
| | - Silvia Angelova
- Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; (N.K.); (S.D.); (V.P.)
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3
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Gerzen OP, Votinova VO, Potoskueva IK, Tzybina AE, Nikitina LV. Direct Effects of Toxic Divalent Cations on Contractile Proteins with Implications for the Heart: Unraveling Mechanisms of Dysfunction. Int J Mol Sci 2023; 24:10579. [PMID: 37445756 DOI: 10.3390/ijms241310579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 06/19/2023] [Accepted: 06/22/2023] [Indexed: 07/15/2023] Open
Abstract
The binding of calcium and magnesium ions to proteins is crucial for regulating heart contraction. However, other divalent cations, including xenobiotics, can accumulate in the myocardium and enter cardiomyocytes, where they can bind to proteins. In this article, we summarized the impact of these cations on myosin ATPase activity and EF-hand proteins, with special attention given to toxic cations. Optimal binding to EF-hand proteins occurs at an ionic radius close to that of Mg2+ and Ca2+. In skeletal Troponin C, Cd2+, Sr2+, Pb2+, Mn2+, Co2+, Ni2+, Ba2+, Mg2+, Zn2+, and trivalent lanthanides can substitute for Ca2+. As myosin ATPase is not a specific MgATPase, Ca2+, Fe2+, Mn2+, Ni2+, and Sr2+ could support myosin ATPase activity. On the other hand, Zn2+ and Cu2 significantly inhibit ATPase activity. The affinity to various divalent cations depends on certain proteins or their isoforms and can alter with amino acid substitution and post-translational modification. Cardiac EF-hand proteins and the myosin ATP-binding pocket are potential molecular targets for toxic cations, which could significantly alter the mechanical characteristics of the heart muscle at the molecular level.
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Affiliation(s)
- Oksana P Gerzen
- Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, 620049 Ekaterinburg, Russia
| | - Veronika O Votinova
- Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, 620049 Ekaterinburg, Russia
| | - Iulia K Potoskueva
- Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, 620049 Ekaterinburg, Russia
| | - Alyona E Tzybina
- Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, 620049 Ekaterinburg, Russia
| | - Larisa V Nikitina
- Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, 620049 Ekaterinburg, Russia
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Mazmanian K, Grauffel C, Dudev T, Lim C. Protein Ca 2+-Sites Prone to Sr 2+ Substitution: Implications for Strontium Therapy. J Phys Chem B 2023. [PMID: 37327495 DOI: 10.1021/acs.jpcb.3c01637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Strontium (Sr), an alkali metal with properties similar to calcium, in the form of soluble salts is used to treat osteoporosis. Despite the information accumulated on the role of Sr2+ as a Ca2+ mimetic in biology and medicine, there is no systematic study of how the outcome of the competition between the two dications depends on the physicochemical properties of (i) the metal ions, (ii) the first- and second-shell ligands, and (iii) the protein matrix. Specifically, the key features of a Ca2+-binding protein that enable Sr2+ to displace Ca2+ remain unclear. To address this, we studied the competition between Ca2+ and Sr2+ in protein Ca2+-binding sites using density functional theory combined with the polarizable continuum model. Our findings indicate that Ca2+-sites with multiple strong charge-donating protein ligands, including one or more bidentately bound Asp-/Glu- that are relatively buried and rigid are protected against Sr2+ attack. On the other hand, Ca2+-sites crowded with multiple protein ligands may be prone to Sr2+ displacement if they are solvent-exposed and flexible enough so that an extra backbone ligand from the outer shell can bind to Sr2+. In addition, solvent-exposed Ca2+ sites with only a few weak charge-donating ligands that can rearrange to fit the strontium's coordination requirements are susceptible to Sr2+ displacement. We provide the physical basis of these results and discuss potential novel protein targets of therapeutic Sr2+.
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Affiliation(s)
- Karine Mazmanian
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
| | - Cédric Grauffel
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
| | - Todor Dudev
- Faculty of Chemistry and Pharmacy, Sofia University, Sofia 1164, Bulgaria
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
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Tan P, Zhao C, Dong Y, Zhang Z, Mei L, Kong Y, Zeng F, Wen Y, Zhao B, Wang J. A Network Pharmacology and Multi-Omics Combination Approach to Reveal the Effect of Strontium on Ca 2+ Metabolism in Bovine Rumen Epithelial Cells. Int J Mol Sci 2023; 24:ijms24119383. [PMID: 37298335 DOI: 10.3390/ijms24119383] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 05/10/2023] [Accepted: 05/21/2023] [Indexed: 06/12/2023] Open
Abstract
Strontium (Sr) belongs to the same group in the periodic table as calcium (Ca). Sr level can serve as an index of rumen Ca absorption capacity; however, the effects of Sr on Ca2+ metabolism are unclear. This study aims to investigate the effect of Sr on Ca2+ metabolism in bovine rumen epithelial cells. The bovine rumen epithelial cells were isolated from the rumen of newborn Holstein male calves (n = 3, 1 day old, 38.0 ± 2.8 kg, fasting). The half maximal inhibitory concentration (IC50) of Sr-treated bovine rumen epithelial cells and cell cycle were used to establish the Sr treatment model. Transcriptomics, proteomics, and network pharmacology were conducted to investigate the core targets of Sr-mediated regulation of Ca2+ metabolism in bovine rumen epithelial cells. The data of transcriptomics and proteomics were analyzed using bioinformatic analysis (Gene Ontology and Kyoto Encyclopedia of genes/protein). Quantitative data were analyzed using one-way ANOVA in GraphPad Prism 8.4.3 and the Shapiro-Wilk test was used for the normality test. Results presented that the IC50 of Sr treatment bovine rumen epithelial cells for 24 h was 43.21 mmol/L, and Sr increased intracellular Ca2+ levels. Multi-omics results demonstrated the differential expression of 770 mRNAs and 2436 proteins after Sr treatment; network pharmacology and reverse transcriptase polymerase chain reaction (RT-PCR) revealed Adenosylhomocysteine hydrolase-like protein 2 (AHCYL2), Semaphoring 3A (SEMA3A), Parathyroid hormone-related protein (PTHLH), Transforming growth factor β2 (TGF-β2), and Cholesterol side-chain cleavage enzyme (CYP11A1) as potential targets for Sr-mediated Ca2+ metabolism regulation. Together these results will improve the current comprehension of the regulatory effect of Sr on Ca2+ metabolism and pave a theoretical basis for Sr application in bovine hypocalcemia.
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Affiliation(s)
- Panpan Tan
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Chenxu Zhao
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Yong Dong
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Zixin Zhang
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Linshan Mei
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Yezi Kong
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Fangyuan Zeng
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Yongqiang Wen
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Baoyu Zhao
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
| | - Jianguo Wang
- College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
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How Theoretical Evaluations Can Generate Guidelines for Designing/Engineering Metalloproteins with Desired Metal Affinity and Selectivity. MOLECULES (BASEL, SWITZERLAND) 2022; 28:molecules28010249. [PMID: 36615442 PMCID: PMC9822464 DOI: 10.3390/molecules28010249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 12/23/2022] [Accepted: 12/25/2022] [Indexed: 12/29/2022]
Abstract
Almost half of all known proteins contain metal co-factors. Crucial for the flawless performance of a metalloprotein is the selection with high fidelity of the cognate metal cation from the surrounding biological fluids. Therefore, elucidating the factors controlling the metal binding and selectivity in metalloproteins is of particular significance. The knowledge thus acquired not only contributes to better understanding of the intimate mechanism of these events but, also, significantly enriches the researcher's toolbox that could be used in designing/engineering novel metalloprotein structures with pre-programmed properties. A powerful tool in aid of deciphering the physical principles behind the processes of metal recognition and selectivity is theoretical modeling of metal-containing biological structures. This review summarizes recent findings in the field with an emphasis on elucidating the major factors governing these processes. The results from theoretical evaluations are discussed. It is the hope that the physical principles evaluated can serve as guidelines in designing/engineering of novel metalloproteins of interest to both science and industry.
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Kircheva N, Toshev N, Dudev T. Holo-chromodulin: competition between the native Cr3+ and other biogenic cations (Fe3+, Fe2+, Mg2+, and Zn2+) for the binding sites. Metallomics 2022; 14:6758515. [PMID: 36220150 DOI: 10.1093/mtomcs/mfac082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 09/30/2022] [Indexed: 11/13/2022]
Abstract
Chromodulin is an oligopeptide that has an essential role for the flawless functioning of insulin. Although the precise sequence of the constituent amino acid residues and the 3D structure of the molecule has not yet been deciphered, it is known that chromodulin contains only four amino acids in the ratio of Glu-: Gly: Cys: Asp- = 4: 2: 2: 2. An indispensable part for the integrity of the molecule in its active (holo-) form are four chromium cations (hence the name) in the oxidation state of 3+, positioned in two metal binding sites containing one and three Cr3+ ions. Experimental works provide some hints/clues concerning the structure of the metal centers, although their exact composition, type, and arrangement of metal ligating entities remain enigmatic. In the current study, we endeavor to unveil possible structure(s) of the Cr3+ loaded binding sites by strictly following the evidence provided by the experimental data. Well-calibrated in silico methodology for optimization and evaluation of Gibbs free energies is applied and gives strong premises for reliably deciphering the composition/structure of chromodulin metal binding sites. Additional computations reveal the advantage of choosing Cr3+ over other tri- (Fe3+) and divalent (Fe2+, Mg2+, and Zn2+) biogenic ions for securing maximum stability of the metal-occupied binding sites.
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Affiliation(s)
- Nikoleta Kircheva
- Institute of Optical Materials and Technologies "Acad. J. Malinowski", Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Nikolay Toshev
- Faculty of Trade Economics and Commodity Science, Plekhanov Russian University of Economics, 117997 Moscow, Russia
| | - Todor Dudev
- Faculty of Chemistry and Pharmacy, Sofia University "St. Kl. Ohridski", 1164 Sofia, Bulgaria
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Kircheva N, Dobrev S, Nikolova V, Angelova S, Dudev T. Theoretical Insight into the Phosphate-Targeted Silver's Antibacterial Action: Differentiation between Gram (+) and Gram (-) Bacteria. Inorg Chem 2022; 61:10089-10100. [PMID: 35724666 DOI: 10.1021/acs.inorgchem.2c01085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although silver is one of the first metals finding broad applications in everyday life, specific key points of the intimate mechanism of its bacteriostatic/bactericidal activity lack explanation. It is widely accepted that the antimicrobial potential of the silver cation depends on the composition and thickness of the bacterial external envelope: the outer membrane in Gram-negative bacteria is more prone to Ag+ attack than the cell wall in Gram-positive bacteria. The major cellular components able to interact strongly with Ag+ (teichoic acids, phospholipids, and lipopolysaccharides) contain mono/diesterified phosphate moieties. By applying a reliable DFT/SMD methodology, we modeled the reactions between the aforementioned constituents in typical Gram-positive and Gram-negative bacteria and hydrated Ag+ species, thus disclosing the factors that govern the process of metal-model ligand complexation. The conducted research indicates thermodynamically possible reactions in all cases but still a greater preference of the Ag+ toward the constituents in Gram-negative bacteria in comparison with their counterparts in Gram-positive bacteria. The observed tendencies shed light on the specific interactions of the silver cation with the modeled phosphate-containing units at the atomic level.
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Affiliation(s)
- Nikoleta Kircheva
- Institute of Optical Materials and Technologies ″Acad. J. Malinowski″, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Stefan Dobrev
- Institute of Optical Materials and Technologies ″Acad. J. Malinowski″, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Valya Nikolova
- Faculty of Chemistry and Pharmacy, Sofia University ″St. Kl. Ohridski″, 1164 Sofia, Bulgaria
| | - Silvia Angelova
- Institute of Optical Materials and Technologies ″Acad. J. Malinowski″, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Todor Dudev
- Faculty of Chemistry and Pharmacy, Sofia University ″St. Kl. Ohridski″, 1164 Sofia, Bulgaria
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What Is Parvalbumin for? Biomolecules 2022; 12:biom12050656. [PMID: 35625584 PMCID: PMC9138604 DOI: 10.3390/biom12050656] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 04/25/2022] [Accepted: 04/28/2022] [Indexed: 12/28/2022] Open
Abstract
Parvalbumin (PA) is a small, acidic, mostly cytosolic Ca2+-binding protein of the EF-hand superfamily. Structural and physical properties of PA are well studied but recently two highly conserved structural motifs consisting of three amino acids each (clusters I and II), which contribute to the hydrophobic core of the EF-hand domains, have been revealed. Despite several decades of studies, physiological functions of PA are still poorly known. Since no target proteins have been revealed for PA so far, it is believed that PA acts as a slow calcium buffer. Numerous experiments on various muscle systems have shown that PA accelerates the relaxation of fast skeletal muscles. It has been found that oxidation of PA by reactive oxygen species (ROS) is conformation-dependent and one more physiological function of PA in fast muscles could be a protection of these cells from ROS. PA is thought to regulate calcium-dependent metabolic and electric processes within the population of gamma-aminobutyric acid (GABA) neurons. Genetic elimination of PA results in changes in GABAergic synaptic transmission. Mammalian oncomodulin (OM), the β isoform of PA, is expressed mostly in cochlear outer hair cells and in vestibular hair cells. OM knockout mice lose their hearing after 3–4 months. It was suggested that, in sensory cells, OM maintains auditory function, most likely affecting outer hair cells’ motility mechanisms.
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Mechanism of Zn 2+ and Ca 2+ Binding to Human S100A1. Biomolecules 2021; 11:biom11121823. [PMID: 34944467 PMCID: PMC8699212 DOI: 10.3390/biom11121823] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 11/26/2021] [Accepted: 11/30/2021] [Indexed: 12/18/2022] Open
Abstract
S100A1 is a member of the S100 family of small ubiquitous Ca2+-binding proteins, which participates in the regulation of cell differentiation, motility, and survival. It exists as homo- or heterodimers. S100A1 has also been shown to bind Zn2+, but the molecular mechanisms of this binding are not yet known. In this work, using ESI-MS and ITC, we demonstrate that S100A1 can coordinate 4 zinc ions per monomer, with two high affinity (KD~4 and 770 nm) and two low affinity sites. Using competitive binding experiments between Ca2+ and Zn2+ and QM/MM molecular modeling we conclude that Zn2+ high affinity sites are located in the EF-hand motifs of S100A1. In addition, two lower affinity sites can bind Zn2+ even when the EF-hands are saturated by Ca2+, resulting in a 2Ca2+:S100A1:2Zn2+ conformer. Finally, we show that, in contrast to calcium, an excess of Zn2+ produces a destabilizing effect on S100A1 structure and leads to its aggregation. We also determined a higher affinity to Ca2+ (KD~0.16 and 24 μm) than was previously reported for S100A1, which would allow this protein to function as a Ca2+/Zn2+-sensor both inside and outside cells, participating in diverse signaling pathways under normal and pathological conditions.
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Ca 2+/Sr 2+ Selectivity in Calcium-Sensing Receptor (CaSR): Implications for Strontium's Anti-Osteoporosis Effect. Biomolecules 2021; 11:biom11111576. [PMID: 34827574 PMCID: PMC8615369 DOI: 10.3390/biom11111576] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 10/07/2021] [Accepted: 10/19/2021] [Indexed: 11/21/2022] Open
Abstract
The extracellular calcium-sensing receptor (CaSR) controls vital bone cell functions such as cell growth, differentiation and apoptosis. The binding of the native agonist (Ca2+) to CaSR activates the receptor, which undergoes structural changes that trigger a cascade of events along the cellular signaling pathways. Strontium (in the form of soluble salts) has been found to also be a CaSR agonist. The activation of the receptor by Sr2+ is considered to be the major mechanism through which strontium exerts its anti-osteoporosis effect, mostly in postmenopausal women. Strontium-activated CaSR initiates a series of signal transduction events resulting in both osteoclast apoptosis and osteoblast differentiation, thus strengthening the bone tissue. The intimate mechanism of Sr2+ activation of CaSR is still enigmatic. Herewith, by employing a combination of density functional theory (DFT) calculations and polarizable continuum model (PCM) computations, we have found that the Ca2+ binding sites 1, 3, and 4 in the activated CaSR, although possessing a different number and type of protein ligands, overall structure and charge state, are all selective for Ca2+ over Sr2+. The three binding sites, regardless of their structural differences, exhibit almost equal metal selectivity if they are flexible and have no geometrical constraints on the incoming Sr2+. In contrast to Ca2+ and Sr2+, Mg2+ constructs, when allowed to fully relax during the optimization process, adopt their stringent six-coordinated octahedral structure at the expense of detaching a one-backbone carbonyl ligand and shifting it to the second coordination layer of the metal. The binding of Mg2+ and Sr2+ to a rigid/inflexible calcium-designed binding pocket requires an additional energy penalty for the binding ion; however, the price for doing so (to be paid by Sr2+) is much less than that of Mg2+. The results obtained delineate the key factors controlling the competition between metal cations for the receptor and shed light on some aspects of strontium’s therapeutic effects.
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