Hybrid penicillin acylases with improved properties for synthesis of β-lactam antibiotics

Enlarging the substrate binding pocket of penicillin G acylase from Achromobacter sp. for highly efficient biosynthesis of β-lactam antibiotics

Penicillin G acylase (PGA) is a key biocatalyst for the enzymatic production of β-lactam antibiotics, which can not only catalyze the synthesis of β-lactam antibiotics but also catalyze the hydrolysis of the products to prepare semi-synthetic antibiotic intermediates. However, the high hydrolysis and low synthesis activities of natural PGAs severely hinder their industrial application. In this study, a combinatorial directed evolution strategy was employed to obtain new PGAs with outstanding performances. The best mutant βF24G/βW154G was obtained from the PGA of Achromobacter sp., which exhibited approximately a 129.62-fold and a 52.55-fold increase in specific activity and synthesis/hydrolysis ratio, respectively, compared to the wild-type AsPGA. Thereafter, this mutant was used to synthesize amoxicillin, cefadroxil, and ampicillin; all conversions > 99% were accomplished in 90-135 min with almost no secondary hydrolysis byproducts produced in the reaction. Molecular dynamics simulation and substrate pocket calculation revealed that substitution of the smallest glycine residue at βF24 and βW154 expanded the binding pocket, thereby facilitating the entry and release of substrates and products. Therefore, this novel mutant is a promising catalyst for the large-scale production of β-lactam antibiotics.

Crystallization and X-ray structure analysis of a thermostable penicillin G acylase from Alcaligenes faecalis

The enzyme penicillin G acylase (EC 3.5.1.11) catalyzes amide-bond cleavage in benzylpenicillin (penicillin G) to yield 6-aminopenicillanic acid, an intermediate chemical used in the production of semisynthetic penicillins. A thermostable penicillin G acylase from Alcaligenes faecalis (AfPGA) has been crystallized using the hanging-drop vapour-diffusion method in two different space groups: C222(1), with unit-cell parameters a = 72.9, b = 86.0, c = 260.2 , and P4(1)2(1)2, with unit-cell parameters a = b = 85.6, c = 298.8 . Data were collected at 293 and the structure was determined using the molecular-replacement method. Like other penicillin acylases, AfPGA belongs to the N-terminal nucleophilic hydrolase superfamily, has undergone post-translational processing and has a serine as the N-terminal residue of the β-chain. A disulfide bridge has been identified in the structure that was not found in the other two known penicillin G cylase structures. The presence of the disulfide bridge is perceived to be one factor that confers higher stability to this enzyme.

Enzymatic synthesis of ampicillin: nonlinear modeling, kinetics estimation, and adaptive control

Nowadays, the use of advanced control strategies in biotechnology is quite low. A main reason is the lack of quality of the data, and the fact that more sophisticated control strategies must be based on a model of the dynamics of bioprocesses. The nonlinearity of the bioprocesses and the absence of cheap and reliable instrumentation require an enhanced modeling effort and identification strategies for the kinetics. The present work approaches modeling and control strategies for the enzymatic synthesis of ampicillin that is carried out inside a fed-batch bioreactor. First, a nonlinear dynamical model of this bioprocess is obtained by using a novel modeling procedure for biotechnology: the bond graph methodology. Second, a high gain observer is designed for the estimation of the imprecisely known kinetics of the synthesis process. Third, by combining an exact linearizing control law with the on-line estimation kinetics algorithm, a nonlinear adaptive control law is designed. The case study discussed shows that a nonlinear feedback control strategy applied to the ampicillin synthesis bioprocess can cope with disturbances, noisy measurements, and parametric uncertainties. Numerical simulations performed with MATLAB environment are included in order to test the behavior and the performances of the proposed estimation and control strategies.

Amino ester hydrolase from Xanthomonas campestris pv. campestris, ATCC 33913 for enzymatic synthesis of ampicillin

α-Amino ester hydrolases (AEH) are a small class of proteins, which are highly specific for hydrolysis or synthesis of α-amino containing amides and esters including β-lactam antibiotics such as ampicillin, amoxicillin, and cephalexin. A BLAST search revealed the sequence of a putative glutaryl 7-aminocephalosporanic acid (GL-7-ACA) acylase 93% identical to a known AEH from Xanthomonas citri. The gene, termed gaa, was cloned from the genomic DNA of Xanthomonas campestris pv. campestris sp. strain ATCC 33913 and the corresponding protein was expressed into Escherichia coli. The purified protein was able to perform both hydrolysis and synthesis of a variety of α-amino β-lactam antibiotics including (R)-ampicillin and cephalexin, with optimal ampicillin hydrolytic activity at 25 °C and pH 6.8, with kinetic parameters of k(cat) of 72.5 s(-1) and K(M) of 1.1 mM. The synthesis parameters α, β(o), and γ for ampicillin, determined here first for this class of proteins, are α = 0.25, β(o) = 42.8 M(-1), and γ = 0.23, and demonstrate the excellent synthetic potential of these enzymes. An extensive study of site-directed mutations around the binding pocket of X. campestris pv. campestris AEH strongly suggests that mutation of almost any first-shell amino acid residues around the active site leads to inactive enzyme, including Y82, Y175, D207, D208, W209, Y222, and E309, in addition to those residues forming the catalytic triad, S174, H340, and D307.

Effects of mutations in the helix G region of horseradish peroxidase

Horseradish peroxidase (HRP) has long attracted intense research interest and is used in many biotechnological fields, including diagnostics, biosensors and biocatalysis. Enhancement of HRP catalytic activity and/or stability would further increase its usefulness. Based on prior art, we substituted solvent-exposed lysine and glutamic acid residues near the proximal helix G (Lys 232, 241; Glu 238, 239) and between helices F and F' (Lys 174). Three single mutants (K232N, K232F, K241N) demonstrated increased stabilities against heat (up to 2-fold) and solvents (up to 4-fold). Stability gains are likely due to improved hydrogen bonding and space-fill characteristics introduced by the relevant substitution. Two double mutants showed stability gains but most double mutations were non-additive and non-synergistic. Substitutions of Lys 174 or Glu 238 were destabilising. Unexpectedly, notable alterations in steady-state Vm/E values occurred with reducing substrate ABTS (2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid)), despite the distance of the mutated positions from the active site.