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Castillo O, Mancillas J, Hughes W, Brancaleon L. Characterization of the interaction of metal-protoporphyrins photosensitizers with β- lactoglobulin. Biophys Chem 2023; 292:106918. [PMID: 36399946 DOI: 10.1016/j.bpc.2022.106918] [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: 07/26/2022] [Revised: 10/24/2022] [Accepted: 10/27/2022] [Indexed: 11/17/2022]
Abstract
We investigated the interaction of a series of metal-protoporphyrins (PPIXs) with bovine β- lactoglobulin (BLG) using a combination of optical spectroscopy and computational simulations. Unlike other studies, the simulations were not merely used to rationalize the experimental data but were employed to refine the experimental data itself. The study was carried out at two pH values, 5 and 9, where BLG is known to have different conformation dictated by the so-called Tanford transition which occurs near pH 7.5. The transition is postulated to regulate access to the interior binding cavity of the protein, thus the pH variation was used as a parameter to investigate whether PPIXs access the central cavity of BLG. The results of our study show that indeed binding increases significantly at alkaline pH, however, the increased affinity is not due to the accessibility of the central cavity. Instead, binding appears to be determined by the tendency of PPIXs to form large inhomogeneous aggregates at acidic pH which hinders interactions with proteins. The binding site determined through a combination of experimental and computational methods is located at the interface between two BLG monomers where the long α-helix segment of the protein face each other. This region is rich in positively charged Lys residues that interact with the propionic acid chains of the protoporphyrins. Establishing the modality of binding between protoporphyrins and BLG would have important consequences for the use of BLG:PPIX complexes in applications such as artificial photoreceptors, artificial metallo-enzymes, delivery of photosensitizers for phototherapy and even solar energy conversion.
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Affiliation(s)
- Omar Castillo
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - James Mancillas
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - William Hughes
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Lorenzo Brancaleon
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA.
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Lopez AJ, Barros EP, Martínez L. On the Interpretation of subtilisin Carlsberg Time-Resolved Fluorescence Anisotropy Decays: Modeling with Classical Simulations. J Chem Inf Model 2020; 60:747-755. [PMID: 31524394 DOI: 10.1021/acs.jcim.9b00539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
In this work, we discuss the challenging time-resolved fluorescence anisotropy of subtilisin Carlsberg (SC), which contains a single Trp residue and is a model fluorescence system. Experimental decay rates and quenching data suggest that the fluorophore should be exposed to water, but the Trp is partially buried in a hydrophobic pocket in the crystallographic structure. In order to study this inconsistency, molecular dynamics simulations were performed to predict the anisotropy decay rates and emission wavelengths of the Trp. We confirmed the inconsistency of the crystallographic structure with the experimentally observed fluorescence data and performed free energy calculations to show that the buried Trp conformation is 2 orders of magnitude (∼3 kcal/mol) more stable than the solvent-exposed one. However, molecular dynamics simulations in which the Trp side chain was restricted to solvent-exposed conformations displayed a maximum Trp emission wavelength shifted toward lower energies and decay rates compatible with the experimentally probed rates. Therefore, if the solvent-exposed conformations are the most important emitters, the experimental anisotropy can be compatibilized with the crystallographic structure. The most likely explanation is that the fluorescence of the most probable conformation in solution, observed in the crystal, is quenched, and this is consistent with the low quantum yield of Trp113 of SC. Additionally, some experiments might have probed denatured or lysed SC structures. SC anisotropy provides an interesting target for the study of fluorescence anisotropy using simulations, which can be used to test and exemplify how modeling can aid the interpretation of experimental data in a system where structure and solution experiments appear to be inconsistent.
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Affiliation(s)
- Alvaro J Lopez
- Institute of Chemistry and Center for Computing in Engineering & Science , University of Campinas , 13083-861 Campinas - SP , Brazil
| | - Emília P Barros
- Institute of Chemistry and Center for Computing in Engineering & Science , University of Campinas , 13083-861 Campinas - SP , Brazil
| | - Leandro Martínez
- Institute of Chemistry and Center for Computing in Engineering & Science , University of Campinas , 13083-861 Campinas - SP , Brazil
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Möckel C, Kubiak J, Schillinger O, Kühnemuth R, Della Corte D, Schröder GF, Willbold D, Strodel B, Seidel CAM, Neudecker P. Integrated NMR, Fluorescence, and Molecular Dynamics Benchmark Study of Protein Mechanics and Hydrodynamics. J Phys Chem B 2018; 123:1453-1480. [DOI: 10.1021/acs.jpcb.8b08903] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Christina Möckel
- Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Jakub Kubiak
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Oliver Schillinger
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
- Institut für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Ralf Kühnemuth
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Dennis Della Corte
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Gunnar F. Schröder
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
- Physics Department, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Dieter Willbold
- Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Birgit Strodel
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
- Institut für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Claus A. M. Seidel
- Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Philipp Neudecker
- Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
- Institute of Complex Systems (ICS-6: Structural Biochemistry), Forschungszentrum Jülich, 52425 Jülich, Germany
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