Broadening the enyzme-catalyzed synthesis of semi-synthetic antibiotics
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Blum, Janna Karen
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Abstract
An alpha-amino ester hydrolase (AEH) applicable to synthesis of semi-synthetic antibiotics was cloned from the genomic DNA of Xanthomonas campestris pv. campestris sp. strain ATCC 33913. AEHs catalyze the synthesis and hydrolysis of alpha-amino beta-lactam antibiotics. The enzyme was characterized for thermodynamic and kinetic parameters. The enzyme shows optimal ampicillin hydrolytic activity at 25C and pH 6.8. The AEH enzymes have been shown to have excellent synthetic capability. Additionally, we demonstrated the first fully aqueous enzymatic one-pot synthesis of ampicillin direct from the natural product penicillin G eliminating the isolation of the intermediate 6-APA. Lastly, to improve the thermostability of the AEH a modified structure-guided consensus model of seven homologous enzymes was generated along with analysis of the B-factors from the available crystal structures of the known AEH from Xanthomonas citri. Our best variant, which is a quadruple mutant, E143H/A275P/N186D/V622I, which has a T_50_30, the temperature at which the half-life is 30 minutes, of 34C and 1.3-fold activity compared to wild-type. Overall, we have successfully improved the understanding of the AEH class of enzymes and applied a novel cascade application, demonstrating AEHs unique applicability in the synthesis of beta-lactam antibiotics. The improved thermostability will further improve the industrial relevance of AEHs.
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2011-03-23
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Dissertation