β-Amyrin biosynthesis: catalytic mechanism and substrate recognition

2017 ◽  
Vol 15 (14) ◽  
pp. 2869-2891 ◽  
Author(s):  
Tsutomu Hoshino
Keyword(s):  
Catalytic Mechanism ◽  
Substrate Recognition ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
The Past ◽  
Substrate Analog ◽  
Analog Experiments

In the past five years, there have been remarkable advances in the study of β-amyrin synthase. This review outlines the catalytic mechanism and substrate recognition in β-amyrin biosynthesis, which have been attained by the site-directed mutagenesis and substrate analog experiments.

Structural and biochemical analyses of theStreptococcus pneumoniaeL,D-carboxypeptidase DacB

2015 ◽  
Vol 71 (2) ◽  
pp. 283-292
Author(s):  
Juan Zhang ◽  
Yi-Hu Yang ◽  
Yong-Liang Jiang ◽  
Cong-Zhao Zhou ◽  
Yuxing Chen
Keyword(s):  
Crystal Structure ◽  
Molecular Docking ◽  
Catalytic Mechanism ◽  
Substrate Recognition ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Binding Properties ◽  
Biochemical Analyses ◽  
Key Residues ◽  
Structural Insights

The L,D-carboxypeptidase DacB plays a key role in the remodelling ofStreptococcus pneumoniaepeptidoglycan during cell division. In order to decipher its substrate-binding properties and catalytic mechanism, the 1.71 Å resolution crystal structure of DacB fromS. pneumoniaeTIGR4 is reported. Structural analyses in combination with comparisons with the recently reported structures of DacB fromS. pneumoniaeD39 and R6 clearly demonstrate that DacB adopts a zinc-dependent carboxypeptidase fold and belongs to the metallopeptidase M15B subfamily. In addition, enzymatic activity assays further confirm that DacB indeed acts as an L,D-carboxypeptidase towards the tetrapeptide L-Ala-D-iGln-L-Lys-D-Ala of the peptidoglycan stem, withKmandkcatvalues of 2.84 ± 0.37 mMand 91.49 ± 0.05 s−1, respectively. Subsequent molecular docking and site-directed mutagenesis enable the assignment of the key residues that bind to the tetrapeptide. Altogether, these findings provide structural insights into substrate recognition in the metallopeptidase M15B subfamily.

scholarly journals Conformational communication mediates the reset step in t6A biosynthesis

2019 ◽  
Vol 47 (12) ◽  
pp. 6551-6567 ◽  
Author(s):  
Amit Luthra ◽  
Naduni Paranagama ◽  
William Swinehart ◽  
Susan Bayooz ◽  
Phuc Phan ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Molecular Docking ◽  
Atpase Activity ◽  
Atp Hydrolysis ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Translational Fidelity ◽  
Substrate Analog ◽  
Binding Cavity ◽  
Saxs Analysis

Abstract The universally conserved N6-threonylcarbamoyladenosine (t6A) modification of tRNA is essential for translational fidelity. In bacteria, t6A biosynthesis starts with the TsaC/TsaC2-catalyzed synthesis of the intermediate threonylcarbamoyl adenylate (TC–AMP), followed by transfer of the threonylcarbamoyl (TC) moiety to adenine-37 of tRNA by the TC-transfer complex comprised of TsaB, TsaD and TsaE subunits and possessing an ATPase activity required for multi-turnover of the t6A cycle. We report a 2.5-Å crystal structure of the T. maritima TC-transfer complex (TmTsaB2D2E2) bound to Mg2+-ATP in the ATPase site, and substrate analog carboxy-AMP in the TC-transfer site. Site directed mutagenesis results show that residues in the conserved Switch I and Switch II motifs of TsaE mediate the ATP hydrolysis-driven reactivation/reset step of the t6A cycle. Further, SAXS analysis of the TmTsaB2D2-tRNA complex in solution reveals bound tRNA lodged in the TsaE binding cavity, confirming our previous biochemical data. Based on the crystal structure and molecular docking of TC–AMP and adenine-37 in the TC-transfer site, we propose a model for the mechanism of TC transfer by this universal biosynthetic system.

Catalytic Mechanism of theStreptomycesK15dd-Transpeptidase/Penicillin-Binding Protein Probed by Site-Directed Mutagenesis and Structural Analysis†,‡

Biochemistry ◽  
2003 ◽  
Vol 42 (10) ◽  
pp. 2895-2906 ◽  
Author(s):  
Noureddine Rhazi ◽  
Paulette Charlier ◽  
Dominique Dehareng ◽  
Danièle Engher ◽  
Marcel Vermeire ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Catalytic Mechanism ◽  
Binding Protein ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Penicillin Binding Protein

scholarly journals Site-directed mutagenesis of proposed active-site residues of penicillin-binding protein 5 from Escherichia coli

1994 ◽  
Vol 303 (2) ◽  
pp. 357-362 ◽  
Author(s):  
M P G van der Linden ◽  
L de Haan ◽  
O Dideberg ◽  
W Keck
Keyword(s):  
Active Site ◽  
Catalytic Mechanism ◽  
Binding Capacity ◽  
Binding Protein ◽  
Complete Loss ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Penicillin Binding Protein ◽  
Wild Type ◽  
Active Site Residues

Alignment of the amino acid sequence of penicillin-binding protein 5 (PBP5) with the sequences of other members of the family of active-site-serine penicillin-interacting enzymes predicted the residues playing a role in the catalytic mechanism of PBP5. Apart from the active-site (Ser44), Lys47, Ser110-Gly-Asn, Asp175 and Lys213-Thr-Gly were identified as the residues making up the conserved boxes of this protein family. To determine the role of these residues, they were replaced using site-directed mutagenesis. The mutant proteins were assayed for their penicillin-binding capacity and DD-carboxypeptidase activity. The Ser44Cys and the Ser44Gly mutants showed a complete loss of both penicillin-binding capacity and DD-carboxypeptidase activity. The Lys47Arg mutant also lost its DD-carboxypeptidase activity but was able to bind and hydrolyse penicillin, albeit at a considerably reduced rate. Mutants in the Ser110-Gly-Asn fingerprint were affected in both acylation and deacylation upon reaction with penicillin and lost their DD-carboxypeptidase activity with the exception of Asn112Ser and Asn112Thr. The Asp175Asn mutant showed wild-type penicillin-binding but a complete loss of DD-carboxypeptidase activity. Mutants of Lys213 lost both penicillin-binding and DD-carboxypeptidase activity except for Lys213His, which still bound penicillin with a k+2/K' of 0.2% of the wild-type value. Mutation of His216 and Thr217 also had a strong effect on DD-carboxypeptidase activity. Thr217Ser and Thr217Ala showed augmented hydrolysis rates for the penicillin acyl-enzyme. This study reveals the residues in the conserved fingerprints to be very important for both DD-carboxypeptidase activity and penicillin-binding, and confirms them to play crucial roles in catalysis.

scholarly journals Role of αArg145 and βArg263 in the active site of penicillin acylase of Escherichia coli

2002 ◽  
Vol 365 (1) ◽  
pp. 303-309 ◽  
Author(s):  
Wynand B.L. ALKEMA ◽  
Antoon K. PRINS ◽  
Erik de VRIES ◽  
Dick B. JANSSEN
Keyword(s):  
Escherichia Coli ◽  
Active Site ◽  
Catalytic Mechanism ◽  
Penicillin Acylase ◽  
Precursor Protein ◽  
Site Directed Mutagenesis ◽  
Penicillin G ◽  
Directed Mutagenesis ◽  
Wild Type ◽  
Arginine Residues

The active site of penicillin acylase of Escherichia coli contains two conserved arginine residues. The function of these arginines, αArg145 and βArg263, was studied by site-directed mutagenesis and kinetic analysis of the mutant enzymes. The mutants αArg145→Leu (αArg145Leu), αArg145Cys and αArg145Lys were normally processed and exported to the periplasm, whereas expression of the mutants βArg263Leu, βArg263Asn and βArg263Lys yielded large amounts of precursor protein in the periplasm, indicating that βArg263 is crucial for efficient processing of the enzyme. Either modification of both arginine residues by 2,3-butanedione or replacement by site-directed mutagenesis yielded enzymes with a decreased specificity (kcat/Km) for 2-nitro-5-[(phenylacetyl)amino]benzoic acid, indicating that both residues are important in catalysis. Compared with the wild type, the αArg145 mutants exhibited a 3–6-fold-increased preference for 6-aminopenicillanic acid as the deacylating nucleophile compared with water. Analysis of the steady-state parameters of these mutants for the hydrolysis of penicillin G and phenylacetamide indicated that destabilization of the Michaelis—Menten complex accounts for the improved activity with β-lactam substrates. Analysis of pH—activity profiles of wild-type enzyme and the βArg263Lys mutant showed that βArg263 has to be positively charged for catalysis, but is not involved in substrate binding. The results provide an insight into the catalytic mechanism of penicillin acylase, in which αArg145 is involved in binding of β-lactam substrates and βArg263 is important both for stabilizing the transition state in the reaction and for correct processing of the precursor protein.

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