scholarly journals Structural Basis for Stereoselective Dehydration and Hydrogen-Bonding Catalysis by the SAM-Dependent Pericyclase LepI

2018 ◽  
Author(s):  
Yujuan Cai ◽  
Yang Hai ◽  
Masao Ohashi ◽  
Cooper S. Jamieson ◽  
Marc Garcia-Borras ◽  
...  
Keyword(s):  
Transition State ◽  
Active Site ◽  
Claisen Rearrangement ◽  
Biochemical Characterization ◽  
Mutational Analysis ◽  
Diels Alder ◽  
Quinone Methide ◽  
Structural Basis ◽  
Active Site Residues ◽  
Transition State Analog

ABSTRACTLepI is an S-adenosylmethionine (SAM)-dependent pericyclase that catalyzes the formation of 2-pyridone natural product leporin C. Biochemical characterization showed LepI can catalyze the stereoselective dehydration to yield a reactive (E)-quinone methide which can undergo a bifurcating intramolecular Diels-Alder (IMDA) and hetero-Diels-Alder (HDA) cyclization from an ambimodal transition state, and a [3,3]-retro-Claisen rearrangement to recycle the IMDA product into leporin C. Here we solved the X-ray crystal structures of SAM-bound LepI, and in complex with a substrate analog, the product leporin C, and a retro-Claisen reaction transition-state analog to understand the structural basis for the multitude of reactions. Structural and mutational analysis revealed how Nature evolves a classic methyltransferase active site into one that can serve as a dehydratase and a multifunctional pericyclase. Catalysis of both sets of reactions employ His133 and Arg295, two active site residues that are not found in canonical methyltransferases. An alternative role of SAM, which is not found to be in direct contact of the substrate, is also proposed.

scholarly journals Structural Comparisons of Cefotaximase (CTX-M-ase) Sub Family 1

2021 ◽  
Vol 12 ◽  
Author(s):  
Ben A. Shurina ◽  
Richard C. Page
Keyword(s):  
Transition State ◽  
Active Site ◽  
Boronic Acid ◽  
Structural Changes ◽  
Surface Patch ◽  
Active Site Residues ◽  
Transition State Analog ◽  
Drug Candidates ◽  
Existing Structures ◽  
New Antibiotics

The cefotaximase or CTX-M, family of serine-β-lactamases represents a significant clinical concern due to the ability for these enzymes to confer resistance to a broad array of β-lactam antibiotics an inhibitors. This behavior lends CTX-M-ases to be classified as extended spectrum β-lactamases (ESBL). Across the family of CTX-M-ases most closely related to CTX-M-1, the structures of CTX-M-15 with a library of different ligands have been solved and serve as the basis of comparison within this review. Herein we focus on the structural changes apparent in structures of CTX-M-15 in complex with diazabicyclooctane (DABCO) and boronic acid transition state analog inhibitors. Interactions between a positive surface patch near the active site and complementary functional groups of the bound inhibitor play key roles in the dictating the conformations of active site residues. The insights provided by analyzing structures of CTX-M-15 in complex with DABCO and boronic acid transition state analog inhibitors and analyzing existing structures of CTX-M-64 offer opportunities to move closer to making predictions as to how CTX-M-ases may interact with potential drug candidates, setting the stage for the further development of new antibiotics and β-lactamase inhibitors.

scholarly journals Important Role for Phylogenetically Invariant PP2Acα Active Site and C-Terminal Residues Revealed by Mutational Analysis in Saccharomyces cerevisiae

Genetics ◽  
2000 ◽  
Vol 156 (1) ◽  
pp. 21-29 ◽  
Author(s):  
David R H Evans ◽  
Brian A Hemmings
Keyword(s):  
Protein Interactions ◽  
Active Site ◽  
Protein Function ◽  
Mutational Analysis ◽  
Yeast Cells ◽  
Temperature Sensitive ◽  
Active Site Residues ◽  
Catalytic Function

Abstract PP2A is a central regulator of eukaryotic signal transduction. The human catalytic subunit PP2Acα functionally replaces the endogenous yeast enzyme, Pph22p, indicating a conservation of function in vivo. Therefore, yeast cells were employed to explore the role of invariant PP2Ac residues. The PP2Acα Y127N substitution abolished essential PP2Ac function in vivo and impaired catalysis severely in vitro, consistent with the prediction from structural studies that Tyr-127 mediates substrate binding and its side chain interacts with the key active site residues His-118 and Asp-88. The V159E substitution similarly impaired PP2Acα catalysis profoundly and may cause global disruption of the active site. Two conditional mutations in the yeast Pph22p protein, F232S and P240H, were found to cause temperature-sensitive impairment of PP2Ac catalytic function in vitro. Thus, the mitotic and cell lysis defects conferred by these mutations result from a loss of PP2Ac enzyme activity. Substitution of the PP2Acα C-terminal Tyr-307 residue by phenylalanine impaired protein function, whereas the Y307D and T304D substitutions abolished essential function in vivo. Nevertheless, Y307D did not reduce PP2Acα catalytic activity significantly in vitro, consistent with an important role for the C terminus in mediating essential protein-protein interactions. Our results identify key residues important for PP2Ac function and characterize new reagents for the study of PP2A in vivo.

scholarly journals A crystallographic study of the Toho-1 β-lactamase acylation mechanism

2014 ◽  
Vol 70 (a1) ◽  
pp. C1207-C1207
Author(s):  
Leighton Coates
Keyword(s):  
Hydrogen Bonding ◽  
Transition State ◽  
Active Site ◽  
Catalytic Mechanism ◽  
Substrate Binding ◽  
Ligand Complex ◽  
Transition State Analog ◽  
Hydrogen Bonding Interactions ◽  
Active Site Region ◽  
Neutron Crystallography

β-lactam antibiotics have been used effectively over several decades against many types of highly virulent bacteria. The predominant cause of resistance to these antibiotics in Gram-negative bacterial pathogens is the production of serine β-lactamase enzymes. A key aspect of the class A serine β-lactamase mechanism that remains unresolved and controversial is the identity of the residue acting as the catalytic base during the acylation reaction. Multiple mechanisms have been proposed for the formation of the acyl-enzyme intermediate that are predicated on understanding the protonation states and hydrogen-bonding interactions among the important residues involved in substrate binding and catalysis of these enzymes. For resolving a controversy of this nature surrounding the catalytic mechanism, neutron crystallography is a powerful complement to X-ray crystallography that can explicitly determine the location of deuterium atoms in proteins, thereby directly revealing the hydrogen-bonding interactions of important amino acid residues. Neutron crystallography was used to unambiguously reveal the ground-state active site protonation states and the resulting hydrogen-bonding network in two ligand-free Toho-1 β-lactamase mutants which provided remarkably clear pictures of the active site region prior to substrate binding and subsequent acylation [1,2] and an acylation transition-state analog, benzothiophene-2-boronic acid (BZB), which was also isotopically enriched with 11B. The neutron structure revealed the locations of all deuterium atoms in the active site region and clearly indicated that Glu166 is protonated in the BZB transition-state analog complex. As a result, the complete hydrogen-bonding pathway throughout the active site region could then deduced for this protein-ligand complex that mimics the acylation tetrahedral intermediate [3].

scholarly journals Structure based protein engineering to confer selectivity of guanine deaminase

2014 ◽  
Vol 70 (a1) ◽  
pp. C437-C437
Author(s):  
Aruna Bitra ◽  
Ruchi Anand
Keyword(s):  
Crystal Structures ◽  
Active Site ◽  
Catalytic Mechanism ◽  
Catalytic Efficiency ◽  
Structural Basis ◽  
Active Site Residues ◽  
X Ray ◽  
Secondary Activity ◽  
Guanine Deaminase ◽  
Differential Selectivity

Guanine deaminases (GDs) are important enzymes involved in both purine metabolism and nucleotide anabolism pathways. Here we present the molecular and catalytic mechanism of NE0047 and use the information obtained to engineer specific enzyme activities. NE0047 from Nitrosomonas europaea was found to be a high fidelity guanine deaminase (catalytic efficiency of 1.2 × 105 M–1 s–1). However; it exhibited secondary activity towards the structurally non-analogous triazine based compound ammeline. The X-ray structure of NE0047 in the presence of the substrate analogue 8-azaguanine help establish that the enzyme exists as a biological dimer and both the proper closure of the C-terminal loop and cross talk via the dimeric interface is crucial for conferring catalytic activity. It was further ascertained that the highly conserved active site residues Glu79 and Glu143 facilitate the deamination reaction by serving as proton shuttles. Moreover, to understand the structural basis of dual substrate specificity, X-ray structures of NE0047 in complex with a series of nucleobase analogs, nucleosides and substrate ammeline were determined. The crystal structures demonstrated that any substitutions in the parent substrates results in the rearrangement of the ligand in a catalytically unfavorable orientation and also impede the closure of catalytically important loop, thereby abrogating activity. However, ammeline was able to adopt a catalytically favorable orientation which, also allowed for proper loop closure. Based on the above knowledge of the crystal structures and the catalytic mechanism, the active site was subsequently engineered to fine-tune NE0047 activity. The mutated versions of the enzyme were designed so that they can function either exclusively as a GD or serve as specific ammeline deaminases. For example, mutations in the active site E143D and N66A confer the enzyme to be an unambiguous GD with no secondary activity towards ammeline. On the other hand, the N66Q mutant of NE0047 only deaminates ammeline. Additionally, a series of crystal structures of the mutant versions were solved that shed light on the structural basis of this differential selectivity.

Catalytic Mechanism of SHCHC Synthase in the Menaquinone Biosynthesis ofEscherichia coli: Identification and Mutational Analysis of the Active Site Residues

Biochemistry ◽  
2009 ◽  
Vol 48 (29) ◽  
pp. 6921-6931 ◽  
Author(s):  
Ming Jiang ◽  
Xiaolei Chen ◽  
Xian-Hui Wu ◽  
Minjiao Chen ◽  
Yun-Dong Wu ◽  
...  
Keyword(s):  
Active Site ◽  
Catalytic Mechanism ◽  
Mutational Analysis ◽  
Ofescherichia Coli ◽  
Active Site Residues

The Roles of Active-Site Residues in the Catalytic Mechanism oftrans-3-Chloroacrylic Acid Dehalogenase:  A Kinetic, NMR, and Mutational Analysis†

Biochemistry ◽  
2004 ◽  
Vol 43 (14) ◽  
pp. 4082-4091 ◽  
Author(s):  
Hugo F. Azurmendi ◽  
Susan C. Wang ◽  
Michael A. Massiah ◽  
Gerrit J. Poelarends ◽  
Christian P. Whitman ◽  
...  
Keyword(s):  
Active Site ◽  
Catalytic Mechanism ◽  
Mutational Analysis ◽  
Active Site Residues ◽  
Chloroacrylic Acid Dehalogenase

scholarly journals Mutational Analysis of Active Site Residues Essential for Sensing of Organic Hydroperoxides by Bacillus subtilis OhrR

2007 ◽  
Vol 189 (19) ◽  
pp. 7069-7076 ◽  
Author(s):  
Sumarin Soonsanga ◽  
Mayuree Fuangthong ◽  
John D. Helmann
Keyword(s):  
Hydrogen Bond ◽  
Bacillus Subtilis ◽  
Conformational Changes ◽  
Active Site ◽  
Mutational Analysis ◽  
High Sensitivity ◽  
Oxidative Modification ◽  
Active Site Residues

ABSTRACT Bacillus subtilis OhrR is the prototype for the one-Cys family of organic peroxide-sensing regulatory proteins. Mutational analyses indicate that the high sensitivity of the active site cysteine (C15) to peroxidation requires three Tyr residues. Y29 and Y40 from the opposing subunit of the functional dimer hydrogen bond with the reactive Cys thiolate, and substitutions at these positions reduce or eliminate the ability of OhrR to respond to organic peroxides. Y19 is also critical for peroxide sensing, and the Ala substitution mutant (OhrR Y19A) is less susceptible to oxidation at the active site C15 in vivo. The Y19A protein also displays decreased sensitivity to peroxide-mediated oxidation in vitro. Y19 is in van der Waals contact with two residues critical for protein function, F16 and R23. The latter residue makes critical contact with the DNA backbone in the OhrR-operator complex. These results indicate that the high sensitivity of the OhrR C15 residue to oxidation requires interactions with the opposed Tyr residues. Oxidative modification of C15 likely disrupts the C15-Y29′-Y40′ hydrogen bond network and thereby initiates conformational changes that reduce the ability of OhrR to bind to its operator site.

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