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Babu CS, Chen JY, Lim C. Solution Ionic Strength Can Modulate Functional Loop Conformations in E. coli Dihydrofolate Reductase. J Phys Chem B 2024; 128:4111-4122. [PMID: 38651832 PMCID: PMC11075089 DOI: 10.1021/acs.jpcb.4c00677] [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] [Received: 01/31/2024] [Revised: 03/19/2024] [Accepted: 04/01/2024] [Indexed: 04/25/2024]
Abstract
The observation of multiple conformations of a functional loop (termed M20) in the Escherichia coli dihydrofolate reductase (ecDHFR) enzyme triggered the proposition that large-scale motions of protein structural elements contribute to enzyme catalysis. The transition of the M20 loop from a closed conformation to an occluded conformation was thought to aid the rate-limiting release of the products. However, the influence of charged species in the solution environment on the observed M20 loop conformations, independent of charged ligands bound to the enzyme, had not been considered. Molecular dynamics simulations of ecDHFR in model CaCl2 solutions of varying molar ionic strengths IM reveal a substantial free energy barrier between occluded and closed M20 loop states at IM exceeding the E. coli threshold (∼0.24 M). This barrier may facilitate crystallization of ecDHFR in the occluded state, consistent with ecDHFR structures obtained at IM exceeding 0.3 M. At lower IM (≤0.15 M), the M20 loop can explore the occluded state, but prefers an open/partially closed conformation, again consistent with ecDHFR structures. Our findings caution against using ecDHFR structures obtained at nonphysiological ionic strengths in interpreting catalytic events or in structure-based drug design.
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Affiliation(s)
- C. Satheesan Babu
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Jih-Ying Chen
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
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Buckley DP, Migaud ME, Tanner JJ. Conformational Preferences of Pyridone Adenine Dinucleotides from Molecular Dynamics Simulations. Int J Mol Sci 2022; 23:11866. [PMID: 36233167 PMCID: PMC9570408 DOI: 10.3390/ijms231911866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 09/23/2022] [Accepted: 10/01/2022] [Indexed: 11/25/2022] Open
Abstract
Pyridone adenine dinucleotides (ox-NADs) are redox inactive derivatives of the enzyme cofactor and substrate nicotinamide adenine dinucleotide (NAD) that have a carbonyl group at the C2, C4, or C6 positions of the nicotinamide ring. These aberrant cofactor analogs accumulate in cells under stress and are potential inhibitors of enzymes that use NAD(H). We studied the conformational landscape of ox-NADs in solution using molecular dynamics simulations. Compared to NAD+ and NADH, 2-ox-NAD and 4-ox-NAD have an enhanced propensity for adopting the anti conformation of the pyridone ribose group, whereas 6-ox-NAD exhibits greater syn potential. Consequently, 2-ox-NAD and 4-ox-NAD have increased preference for folding into compact conformations, whereas 6-ox-NAD is more extended. ox-NADs have distinctive preferences for the orientation of the pyridone amide group, which are driven by intramolecular hydrogen bonding and steric interactions. These conformational preferences are compared to those of protein-bound NAD(H). Our results may help in identifying enzymes targeted by ox-NADs.
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Affiliation(s)
- David P. Buckley
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - Marie E. Migaud
- Mitchell Cancer Institute, Department of Pharmacology, College of Medicine, University of South Alabama, Mobile, AL 36604, USA
| | - John J. Tanner
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
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Babu CS, Lim C. Influence of solution ionic strength on the stabilities of M20 loop conformations in apo E. coli dihydrofolate reductase. J Chem Phys 2021; 154:195103. [PMID: 34240890 DOI: 10.1063/5.0048968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Interactions among ions and their specific interactions with macromolecular solutes are known to play a central role in biomolecular stability. However, similar effects in the conformational stability of protein loops that play functional roles, such as binding ligands, proteins, and DNA/RNA molecules, remain relatively unexplored. A well-characterized enzyme that has such a functional loop is Escherichia coli dihydrofolate reductase (ecDHFR), whose so-called M20 loop has been observed in three ordered conformations in crystal structures. To explore how solution ionic strengths may affect the M20 loop conformation, we proposed a reaction coordinate that could quantitatively describe the loop conformation and used it to classify the loop conformations in representative ecDHFR x-ray structures crystallized in varying ionic strengths. The Protein Data Bank survey indicates that at ionic strengths (I) below the intracellular ion concentration-derived ionic strength in E. coli (I ≤ 0.237M), the ecDHFR M20 loop tends to adopt open/closed conformations, and rarely an occluded loop state, but when I is >0.237M, the loop tends to adopt closed/occluded conformations. Distance-dependent electrostatic potentials around the most mobile M20 loop region from molecular dynamics simulations of ecDHFR in equilibrated CaCl2 solutions of varying ionic strengths show that high ionic strengths (I = 0.75/1.5M) can preferentially stabilize the loop in closed/occluded conformations. These results nicely correlate with conformations derived from ecDHFR structures crystallized in varying ionic strengths. Altogether, our results suggest caution in linking M20 loop conformations derived from crystal structures solved at ionic strengths beyond that tolerated by E. coli to the ecDHFR function.
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Affiliation(s)
- C Satheesan Babu
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
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Gorbunova IA, Sasin ME, Rubayo-Soneira J, Smolin AG, Vasyutinskii OS. Two-Photon Excited Fluorescence Dynamics in NADH in Water-Methanol Solutions: The Role of Conformation States. J Phys Chem B 2020; 124:10682-10697. [PMID: 33175534 DOI: 10.1021/acs.jpcb.0c07620] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dynamics of polarized fluorescence in reduced nicotinamide adenine dinucleotide (NADH) at 460 nm under two-photon excitation at 720 nm by femtosecond laser pulses in water-methanol solutions has been studied experimentally and theoretically as a function of methanol concentration. A number of fluorescence parameters have been determined from experiment by means of the global fit procedure and then compared with the results reported by other authors. A comprehensive analysis of experimental errors was made. Ab initio calculations of the structure of NADH in water and methanol and of β-nicotinamide mononucleotide (NMNH) in vacuum have been carried out for clarifying the role of decay time heterogeneity. The main results obtained are as follows. An explanation of the heterogeneity in the measured fluorescence decay times in NADH has been suggested based on the influence of the internal molecular electric field in the nicotinamide ring on nonradiative decay rates. We suggest that different charge distributions in the cis and trans configurations result in different internal electrostatic field distributions that lead to the decay time heterogeneity. A slight but noticeable rise of the fluorescence decay times τ1 and τ2 with methanol concentration was observed and treated as a minor effect of a nonradiative relaxation slowing due to the decrease in solution polarity. Relative concentrations of the folded and unfolded NADH conformations in solutions have been determined using a new method of analysis of the rotational diffusion time τr as a function of methanol concentration on the basis of the Stokes-Einstein-Debye equation. The analysis of the fluorescence anisotropy parameters obtained under linearly and circularly polarized excitation and the parameter Ω has been carried out and resulted in the determination of the two-photon excitation tensor components and suggested the existence of two excitation channels with comparable intensities. These were the longitudinal excitation channel dominated by the diagonal tensor component Szz and the mixed excitation channel dominated by the off-diagonal tensor components |Sxz2 + Syz2|1/2.
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Affiliation(s)
| | - Maxim E Sasin
- Ioffe Institute, 26 Polytekhnicheskaya, St.Petersburg 194021, Russia
| | - Jesus Rubayo-Soneira
- Universidad de La Habana, Instituto Superior de Tecnologías y Ciencias Aplicadas, La Habana 10400, Cuba
| | - Andrey G Smolin
- Ioffe Institute, 26 Polytekhnicheskaya, St.Petersburg 194021, Russia
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Sousa SF, Calixto AR, Ferreira P, Ramos MJ, Lim C, Fernandes PA. Activation Free Energy, Substrate Binding Free Energy, and Enzyme Efficiency Fall in a Very Narrow Range of Values for Most Enzymes. ACS Catal 2020. [DOI: 10.1021/acscatal.0c01947] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sérgio F. Sousa
- UCIBIO, REQUIMTE, Departamento de Quı́mica e Bioquı́mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal
| | - Ana R. Calixto
- UCIBIO, REQUIMTE, Departamento de Quı́mica e Bioquı́mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal
| | - Pedro Ferreira
- UCIBIO, REQUIMTE, Departamento de Quı́mica e Bioquı́mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal
| | - Maria J. Ramos
- UCIBIO, REQUIMTE, Departamento de Quı́mica e Bioquı́mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
- Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Pedro A. Fernandes
- UCIBIO, REQUIMTE, Departamento de Quı́mica e Bioquı́mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal
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Understanding (R) Specific Carbonyl Reductase from Candida parapsilosis ATCC 7330 [CpCR]: Substrate Scope, Kinetic Studies and the Role of Zinc. Catalysts 2019. [DOI: 10.3390/catal9090702] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
CpCR, an (R) specific carbonyl reductase, so named because it gave (R)-alcohols on asymmetric reduction of ketones and ketoesters, is a recombinantly expressed enzyme from Candida parapsilosis ATCC 7330. It turns out to be a better aldehyde reductase and catalyses cofactor (NADPH) specific reduction of aliphatic and aromatic aldehydes. Kinetics studies against benzaldehyde and 2,4-dichlorobenzaldehyde show that the enzyme affinity and rate of reaction change significantly upon substitution on the benzene ring of benzaldehyde. CpCR, an MDR (medium chain reductase/dehydrogenase) containing both structural and catalytic Zn atoms, exists as a dimer, unlike the (S) specific reductase (SRED) from the same yeast which can exist in both dimeric and tetrameric forms. Divalent metal salts inhibit the enzyme even at nanomolar concentrations. EDTA chelation decreases CpCR activity. However, chelation done after the enzyme is pre-incubated with the NADPH retains most of the activity implying that Zn removal is largely prevented by the formation of the enzyme-cofactor complex.
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