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Rodríguez HA, Bickelhaupt FM, Fernández I. Origin of the Bürgi-Dunitz Angle. Chemphyschem 2023; 24:e202300379. [PMID: 37306022 DOI: 10.1002/cphc.202300379] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 06/09/2023] [Accepted: 06/12/2023] [Indexed: 06/13/2023]
Abstract
The Bürgi-Dunitz (BD) angle plays a pivotal role in organic chemistry to rationalize the nucleophilic addition to carbonyl groups. Yet, the origin of the obtuse trajectory of the nucleophile remains incompletely understood. Herein, we quantify the importance of the underlying physical factors quantum chemically. The obtuse BD angle appears to originate from the concerted action of a reduced Pauli repulsion between the nucleophile HOMO and carbonyl π bond, a more stabilizing HOMO-π*-LUMO(C=O) interaction, as well as a more favorable electrostatic attraction.
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Affiliation(s)
- Humberto A Rodríguez
- Departamento de Química Orgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Facultad de Ciencias Químicas, Universidad Complutense de Madrid Ciudad Universitaria, 28040-, Madrid, Spain
- Instituto de Productos Naturales y Agrobiología (IPNA), Consejo Superior de Investigaciones Científicas (CSIC), 38206-, La Laguna, Tenerife, Spain
| | - F Matthias Bickelhaupt
- Theoretical Chemistry, Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, The Netherlands
- Institute for Molecules and Materials (IMM), Radboud University, Nijmegen, The Netherlands
- Department of Chemical Sciences, University of Johannesburg, South Africa
| | - Israel Fernández
- Departamento de Química Orgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Facultad de Ciencias Químicas, Universidad Complutense de Madrid Ciudad Universitaria, 28040-, Madrid, Spain
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SufB intein splicing in Mycobacterium tuberculosis is influenced by two remote conserved N-extein histidines. Biosci Rep 2022; 42:230724. [PMID: 35234249 PMCID: PMC8891592 DOI: 10.1042/bsr20212207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 01/11/2022] [Accepted: 01/27/2022] [Indexed: 11/24/2022] Open
Abstract
Inteins are auto-processing domains that implement a multistep biochemical reaction termed protein splicing, marked by cleavage and formation of peptide bonds. They excise from a precursor protein, generating a functional protein via covalent bonding of flanking exteins. We report the kinetic study of splicing and cleavage reaction in [Fe–S] cluster assembly protein SufB from Mycobacterium tuberculosis (Mtu). Although it follows a canonical intein splicing pathway, distinct features are added by extein residues present in the active site. Sequence analysis identified two conserved histidines in the N-extein region; His-5 and His-38. Kinetic analyses of His-5Ala and His-38Ala SufB mutants exhibited significant reductions in splicing and cleavage rates relative to the SufB wildtype (WT) precursor protein. Structural analysis and molecular dynamics (MD) simulations suggested that Mtu SufB displays a unique mechanism where two remote histidines work concurrently to facilitate N-terminal cleavage reaction. His-38 is stabilized by the solvent-exposed His-5, and can impact N–S acyl shift by direct interaction with the catalytic Cys1. Development of inteins as biotechnological tools or as pathogen-specific novel antimicrobial targets requires a more complete understanding of such unexpected roles of conserved extein residues in protein splicing.
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Affiliation(s)
- Mark Aldren M. Feliciano
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Brian Gold
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States
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Mechanism, origin of diastereoselectivity and factors affecting reaction efficiency of serine/threonine ligation: A computational study. Tetrahedron 2020. [DOI: 10.1016/j.tet.2020.131143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Pettinger J, Carter M, Jones K, Cheeseman MD. Kinetic Optimization of Lysine-Targeting Covalent Inhibitors of HSP72. J Med Chem 2019; 62:11383-11398. [PMID: 31725295 PMCID: PMC6959841 DOI: 10.1021/acs.jmedchem.9b01709] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Indexed: 12/30/2022]
Abstract
The covalent inhibition mechanism of action, which overcomes competition with high-affinity, high-abundance substrates of challenging protein targets, can deliver effective chemical probes and drugs. The success of this strategy has centered on exposed cysteine residues as nucleophiles but the low abundance of cysteine in the proteome has limited its application. We have recently reported our discovery that lysine-56 in the difficult-to-drug target HSP72 could form a covalent bond with a small-molecule inhibitor. We now disclose the optimization of these targeted covalent inhibitors using rational design. Essential to our optimization was the development of a new covalent fluorescence polarization assay, which allows for the direct measurement of the key kinetic parameter in covalent inhibitor design, kinact/KI, extrapolation of the underlying parameters, kinact and Ki, and direct comparison to reversible analogues. Using our approach, we demonstrate a >100-fold enhancement in covalent efficiency and key learnings in lysine-selective electrophile optimization.
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Affiliation(s)
- Jonathan Pettinger
- Cancer Research UK Cancer
Therapeutics Unit, The Institute of Cancer
Research, London SW7 3RP, United Kingdom
| | - Michael Carter
- Cancer Research UK Cancer
Therapeutics Unit, The Institute of Cancer
Research, London SW7 3RP, United Kingdom
| | - Keith Jones
- Cancer Research UK Cancer
Therapeutics Unit, The Institute of Cancer
Research, London SW7 3RP, United Kingdom
| | - Matthew D. Cheeseman
- Cancer Research UK Cancer
Therapeutics Unit, The Institute of Cancer
Research, London SW7 3RP, United Kingdom
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Ageshina AA, Chesnokov GA, Topchiy MA, Alabugin IV, Nechaev MS, Asachenko AF. Making endo-cyclizations favorable again: a conceptually new synthetic approach to benzotriazoles via azide group directed lithiation/cyclization of 2-azidoaryl bromides. Org Biomol Chem 2019; 17:4523-4534. [PMID: 30994147 DOI: 10.1039/c9ob00615j] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Although benzotriazoles are important and ubiquitous, currently there is only one conceptual approach to their synthesis: bridging the two ortho-amino groups with an electrophilic nitrogen atom. Herein, we disclose a new practical alternative - the endo-cyclization of 2-azidoaryl lithiums obtained in situ from 2-azido-aryl bromides. The scope of the reaction is illustrated using twenty-four examples with a variety of alkyl, alkoxy, perfluoroalkyl, and halogen substituents. We found that the directing effect of the azide group allows selective metal-halogen exchange in aryl azides containing several bromine atoms. Furthermore, (2-bromophenyl)diazomethane undergoes similar cyclization to give an indazole. Thus, cyclizations of aryl lithiums containing an ortho-X = Y = Z group emerge as a new general approach for the synthesis of aromatic heterocycles. DFT computations suggested that the observed endo-selectivity applies to the anionic cyclizations of other functionalities that undergo "1,1-additions" (i.e., azides, diazo compounds, and isonitriles). In contrast, cyclizations with the heteroatomic functionalities that follow the "1,2-addition" pattern (cyanates, thiocyanates, isocyanates, isothiocyanates, and nitriles) prefer the exo-cyclization path. Hence, such reactions expand the current understanding of stereoelectronic factors in anionic cyclizations.
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Affiliation(s)
- Alexandra A Ageshina
- A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 119991 Moscow, Leninskiy prospect 29, Russian Federation.
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Jiang YY, Zhu L, Fan X, Zhang Q, Fu YJ, Li H, Hu B, Bi S. A computational study on H 2S release and amide formation from thionoesters and cysteine. Org Biomol Chem 2019; 17:5771-5778. [PMID: 31135017 DOI: 10.1039/c9ob00854c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The recognition of the biological activity of H2S has drawn much attention to the development of biocompatible H2S release reactions. Thiol-, particularly cysteine-triggered systems which mimic the enzymatic conversion of cysteine or homocysteine to H2S have been intensively reported recently. Herein, a density functional theory (DFT) study was performed to address the reaction mechanism of H2S release and potential amide bond formation from thionoesters and cysteine to gain deeper mechanistic insights. Three possible mechanisms were considered and we found that the one starting from the nucleophilic addition of the ionized mercapto of cysteine on thionoester to generate a dithioester intermediate (Path A) is kinetically favored over the others starting from the nucleophilic addition of the amine of cysteine to generate thionoamide intermediates (Paths B and C). Dithioester then undergoes intramolecular nucleophilic addition of an amine group and the rate-limiting water-assisted proton transfer to generate a cyclic thiol intermediate, and finally affords H2S and dihydrothiazole via water-assisted elimination. The hydrolysis of thionoamide or dihydrothiazole to produce amide is highly difficult under neutral conditions but is operative under strong basic conditions, which explains the experimental observation that dihydrothiazole rather than amide is the major product. Meanwhile, the ring opening reaction of the cyclic thiol intermediate to form the more stable thionoamide is detrimental to H2S release and becomes competitive under basic conditions.
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Affiliation(s)
- Yuan-Ye Jiang
- School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, People's Republic of China.
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Friedel K, Popp MA, Matern JCJ, Gazdag EM, Thiel IV, Volkmann G, Blankenfeldt W, Mootz HD. A functional interplay between intein and extein sequences in protein splicing compensates for the essential block B histidine. Chem Sci 2018; 10:239-251. [PMID: 30713635 PMCID: PMC6333167 DOI: 10.1039/c8sc01074a] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 10/03/2018] [Indexed: 01/28/2023] Open
Abstract
Steric bulk can compensate for a catalytically critical histidine in an intein's active site and promote the N–S acyl shift.
Inteins remove themselves from a precursor protein by protein splicing. Due to the concomitant structural changes of the host protein, this self-processing reaction has enabled many applications in protein biotechnology and chemical biology. We show that the evolved M86 mutant of the Ssp DnaB intein displays a significantly improved tolerance towards non-native amino acids at the N-terminally flanking (–1) extein position compared to the parent intein, in the form of both an artificially trans-splicing split intein and the cis-splicing mini-intein. Surprisingly, side chains with increased steric bulk compared to the native Gly(–1) residue, including d-amino acids, were found to compensate for the essential block B histidine in His73Ala mutants in the initial N–S acyl shift of the protein splicing pathway. In the case of the M86 intein, large (–1) side chains can even rescue protein splicing activity as a whole. With the comparison of three crystal structures, namely of the M86 intein as well as of its Gly(–1)Phe and Gly(–1)Phe/His73Ala mutants, our data supports a model in which the intein's active site can exert a strain by varying mechanisms on the different angles of the scissile bond at the extein–intein junction to effect a ground-state destabilization. The compensatory mechanism of the block B histidine is the first example for the direct functional role of an extein residue in protein splicing. It sheds new light on the extein–intein interplay and on possible consequences of their co-evolution as well as on the laboratory engineering of improved inteins.
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Affiliation(s)
- Kristina Friedel
- Institute of Biochemistry , University of Muenster , Wilhelm-Klemm-Str. 2 , 48149 Münster , Germany .
| | - Monika A Popp
- Structure and Function of Proteins , Helmholtz Centre for Infection Research , Inhoffenstraße 7 , 38124 , Braunschweig , Germany
| | - Julian C J Matern
- Institute of Biochemistry , University of Muenster , Wilhelm-Klemm-Str. 2 , 48149 Münster , Germany .
| | - Emerich M Gazdag
- Structure and Function of Proteins , Helmholtz Centre for Infection Research , Inhoffenstraße 7 , 38124 , Braunschweig , Germany
| | - Ilka V Thiel
- Institute of Biochemistry , University of Muenster , Wilhelm-Klemm-Str. 2 , 48149 Münster , Germany .
| | - Gerrit Volkmann
- Institute of Biochemistry , University of Muenster , Wilhelm-Klemm-Str. 2 , 48149 Münster , Germany .
| | - Wulf Blankenfeldt
- Structure and Function of Proteins , Helmholtz Centre for Infection Research , Inhoffenstraße 7 , 38124 , Braunschweig , Germany.,Institute for Biochemistry, Biotechnology and Bioinformatics , Technische Universität Braunschweig , Spielmannstraße 7 , 38106 Braunschweig , Germany
| | - Henning D Mootz
- Institute of Biochemistry , University of Muenster , Wilhelm-Klemm-Str. 2 , 48149 Münster , Germany .
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