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Higbee PS, Dayhoff GW, Anbanandam A, Varma S, Daughdrill G. Structural Adaptation of Secondary p53 Binding Sites on MDM2 and MDMX. J Mol Biol 2024; 436:168626. [PMID: 38810774 DOI: 10.1016/j.jmb.2024.168626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Revised: 04/24/2024] [Accepted: 05/18/2024] [Indexed: 05/31/2024]
Abstract
The thermodynamics of secondary p53 binding sites on MDM2 and MDMX were evaluated using p53 peptides containing residues 16-29, 17-35, and 1-73. All the peptides had large, negative heat capacity (ΔCp), consistent with the burial of p53 residues F19, W23, and L26 in the primary binding sites of MDM2 and MDMX. MDMX has a higher affinity and more negative ΔCp than MDM2 for p5317-35, which is due to MDMX stabilization and not additional interactions with the secondary binding site. ΔCp measurements show binding to the secondary site is inhibited by the disordered tails of MDM2 for WT p53 but not a more helical mutant where proline 27 is changed to alanine. This result is supported by all-atom molecular dynamics simulations showing that p53 residues 30-35 turn away from the disordered tails of MDM2 in P27A17-35 and make direct contact with this region in p5317-35. Molecular dynamics simulations also suggest that an intramolecular methionine-aromatic motif found in both MDM2 and MDMX structurally adapts to support multiple p53 binding modes with the secondary site. ΔCp measurements also show that tighter binding of the P27A mutant to MDM2 and MDMX is due to increased helicity, which reduces the energetic penalty associated with coupled folding and binding. Our results will facilitate the design of selective p53 inhibitors for MDM2 and MDMX.
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Affiliation(s)
- Pirada Serena Higbee
- The Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA
| | - Guy W Dayhoff
- The Department of Chemistry, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA
| | - Asokan Anbanandam
- The Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA
| | - Sameer Varma
- The Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA; The Department of Physics, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA
| | - Gary Daughdrill
- The Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33620, USA.
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Nan Y, MacKerell AD. Balancing Group I Monatomic Ion-Polar Compound Interactions for Condensed Phase Simulation in the Polarizable Drude Force Field. J Chem Theory Comput 2024; 20:3242-3257. [PMID: 38588064 PMCID: PMC11039353 DOI: 10.1021/acs.jctc.3c01380] [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] [Indexed: 04/10/2024]
Abstract
Molecular dynamics (MD) simulations are a commonly used method for investigating molecular behavior at the atomic level. Achieving reliable MD simulation results necessitates the use of an accurate force field. In the present work, we present a protocol to enhance the quality of group 1 monatomic ions (specifically Li+, Na+, K+, Rb+, and Cs+) with respect to their interactions with common polar model compounds in biomolecules in condensed phases in the context of the Drude polarizable force field. Instead of adjusting preexisting individual parameters for ions, model compounds, and water, we employ atom-pair specific Lennard-Jones (LJ) (known as NBFIX in CHARMM) and through-space Thole dipole screening (NBTHOLE) terms to fine-tune the balance of ion-model compound, ion-water, and model compound-water interactions. This involved establishing a protocol for the optimization of NBFIX and NBTHOLE parameters targeting the difference between molecular mechanical (MM) and quantum mechanical (QM) potential energy scans (PES). It is shown that targeting PES involving complexes that include multiple model compounds and/or ions as trimers and tetramers yields parameters that produce condensed phase properties in agreement with experimental data. Validation of this protocol involved the reproduction of experimental thermodynamic benchmarks, including solvation free energies of ions in methanol and N-methylacetamide, osmotic pressures, ionic conductivities, and diffusion coefficients within the condensed phase. These results show the importance of including more complex ion-model compound complexes beyond dimers in the QM target data to account for many-body effects during parameter fitting. The presented parameters represent a significant refinement of the Drude polarizable force field, which will lead to improved accuracy for modeling ion-biomolecular interactions.
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Affiliation(s)
- Yiling Nan
- University of Maryland Computer-Aided Drug Design Center, Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201 MD
| | - Alexander D. MacKerell
- University of Maryland Computer-Aided Drug Design Center, Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201 MD
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Delgado JM, Nagy PR, Varma S. Polarizable AMOEBA Model for Simulating Mg 2+·Protein·Nucleotide Complexes. J Chem Inf Model 2024; 64:378-392. [PMID: 38051630 DOI: 10.1021/acs.jcim.3c01513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Molecular mechanics (MM) simulations have the potential to provide detailed insights into the mechanisms of enzymes that utilize nucleotides as cofactors. In most cases, the activities of these enzymes also require the binding of divalent cations to catalytic sites. However, modeling divalent cations in MM simulations has been challenging. The inclusion of explicit polarization was considered promising, but despite improvements over nonpolarizable force fields and despite the inclusion of "Nonbonded-fix (NB-fix)" corrections, errors in interaction energies of divalent cations with proteins remain large. Importantly, the application of these models fails to reproduce the experimental structural data on Mg2+·Protein·ATP complexes. Focusing on these complexes, here we provide a systematic assessment of the polarizable AMOEBA model and recommend critical changes that substantially improve its predictive performance. Our key results are as follows. We first show that our recent revision of the AMOEBA protein model (AMOEBABIO18-HFC), which contains high field corrections (HFCs) to induced dipoles, dramatically improves Mg2+-protein interaction energies, reducing the mean absolute error (MAE) from 17 to 10 kcal/mol. This further supports the general applicability of AMOEBABIO18-HFC. The inclusion of many-body NB-fix corrections further reduces MAE to 6 kcal/mol, which amounts to less than 2% error. The errors are estimated with respect to vdW-inclusive density functional theory that we benchmark against CCSD(T) calculations and experiments. We also present a new model of ATP with revised polarization parameters to better capture its high field response, as well as new vdW and dihedral parameters. The ATP model accurately predicts experimental Mg2+-ATP binding free energy in the aqueous phase and provides new insights into how Mg2+ associates with ATP. Finally, we show that molecular dynamics (MD) simulations of Mg2+·Kinase·ATP complexes carried out with these improvements lead to a better agreement in global and local catalytic site structures between MD and X-ray crystallography.
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Affiliation(s)
- Julian M Delgado
- Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Avenue, Tampa, Florida 33620, United States
| | - Péter R Nagy
- Department of Physical Chemistry and Materials Science, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Műegyetem rkp. 3., Budapest H-1111, Hungary
- HUN-REN-BME Quantum Chemistry Research Group, Műegyetem rkp. 3., Budapest H-1111, Hungary
- MTA-BME Lendület Quantum Chemistry Research Group, Műegyetem rkp. 3., Budapest H-1111, Hungary
| | - Sameer Varma
- Department of Molecular Biosciences, University of South Florida, 4202 E. Fowler Avenue, Tampa, Florida 33620, United States
- Department of Physics, University of South Florida, 4202 E. Fowler Avenue, Tampa, Florida 33620, United States
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Cueny RR, Varma S, Schmidt KH, Keck JL. Biochemical properties of naturally occurring human bloom helicase variants. PLoS One 2023; 18:e0281524. [PMID: 37267408 DOI: 10.1371/journal.pone.0281524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 05/22/2023] [Indexed: 06/04/2023] Open
Abstract
Bloom syndrome helicase (BLM) is a RecQ-family helicase implicated in a variety of cellular processes, including DNA replication, DNA repair, and telomere maintenance. Mutations in human BLM cause Bloom syndrome (BS), an autosomal recessive disorder that leads to myriad negative health impacts including a predisposition to cancer. BS-causing mutations in BLM often negatively impact BLM ATPase and helicase activity. While BLM mutations that cause BS have been well characterized both in vitro and in vivo, there are other less studied BLM mutations that exist in the human population that do not lead to BS. Two of these non-BS mutations, encoding BLM P868L and BLM G1120R, when homozygous, increase sister chromatid exchanges in human cells. To characterize these naturally occurring BLM mutant proteins in vitro, we purified the BLM catalytic core (BLMcore, residues 636-1298) with either the P868L or G1120R substitution. We also purified a BLMcore K869A K870A mutant protein, which alters a lysine-rich loop proximal to the P868 residue. We found that BLMcore P868L and G1120R proteins were both able to hydrolyze ATP, bind diverse DNA substrates, and unwind G-quadruplex and duplex DNA structures. Molecular dynamics simulations suggest that the P868L substitution weakens the DNA interaction with the winged-helix domain of BLM and alters the orientation of one lobe of the ATPase domain. Because BLMcore P868L and G1120R retain helicase function in vitro, it is likely that the increased genome instability is caused by specific impacts of the mutant proteins in vivo. Interestingly, we found that BLMcore K869A K870A has diminished ATPase activity, weakened binding to duplex DNA structures, and less robust helicase activity compared to wild-type BLMcore. Thus, the lysine-rich loop may have an important role in ATPase activity and specific binding and DNA unwinding functions in BLM.
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Affiliation(s)
- Rachel R Cueny
- Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI, United States of America
| | - Sameer Varma
- Department of Cell Biology, Microbiology, and Molecular Biology, University of South Florida, Tampa, FL, United States of America
- Department of Physics, University of South Florida, Tampa, FL, United States of America
| | - Kristina H Schmidt
- Department of Cell Biology, Microbiology, and Molecular Biology, University of South Florida, Tampa, FL, United States of America
| | - James L Keck
- Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI, United States of America
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Schöller A, Woodcock HL, Boresch S. Exploring Routes to Enhance the Calculation of Free Energy Differences via Non-Equilibrium Work SQM/MM Switching Simulations Using Hybrid Charge Intermediates between MM and SQM Levels of Theory or Non-Linear Switching Schemes. Molecules 2023; 28:4006. [PMID: 37241747 PMCID: PMC10222338 DOI: 10.3390/molecules28104006] [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: 03/27/2023] [Revised: 04/25/2023] [Accepted: 04/26/2023] [Indexed: 05/28/2023] Open
Abstract
Non-equilibrium work switching simulations and Jarzynski's equation are a reliable method for computing free energy differences, ΔAlow→high, between two levels of theory, such as a pure molecular mechanical (MM) and a quantum mechanical/molecular mechanical (QM/MM) description of a system of interest. Despite the inherent parallelism, the computational cost of this approach can quickly become very high. This is particularly true for systems where the core region, the part of the system to be described at different levels of theory, is embedded in an environment such as explicit solvent water. We find that even for relatively simple solute-water systems, switching lengths of at least 5 ps are necessary to compute ΔAlow→high reliably. In this study, we investigate two approaches towards an affordable protocol, with an emphasis on keeping the switching length well below 5 ps. Inserting a hybrid charge intermediate state with modified partial charges, which resembles the charge distribution of the desired high level, makes it possible to obtain reliable calculations with 2 ps switches. Attempts using step-wise linear switching paths, on the other hand, did not lead to improvement, i.e., a faster convergence for all systems. To understand these findings, we analyzed the solutes' properties as a function of the partial charges used and the number of water molecules in direct contact with the solute, and studied the time needed for water molecules to reorient themselves upon a change in the solute's charge distribution.
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Affiliation(s)
- Andreas Schöller
- Faculty of Chemistry, Department of Computational Biological Chemistry, University of Vienna, Währingerstr. 17, A-1090 Vienna, Austria
- Vienna Doctoral School in Chemistry (DoSChem), University of Vienna, Währingerstr. 42, A-1090 Vienna, Austria
| | - H. Lee Woodcock
- Department of Chemistry, University of South Florida, 4202 E. Fowler Ave., CHE205, Tampa, FL 33620-5250, USA;
| | - Stefan Boresch
- Faculty of Chemistry, Department of Computational Biological Chemistry, University of Vienna, Währingerstr. 17, A-1090 Vienna, Austria
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