Cloning, Overexpression, and Characterization of a Novel Thermostable Penicillin G Acylase from Achromobacter xylosoxidans : Probing the Molecular Basis for Its High Thermostability

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Abstract
The gene encoding a novel penicillin G acylase (PGA), designated pgaW, was cloned from Achromobacter xylosoxidans and overexpressed in Escherichia coli. The pgaW gene contains an open reading frame of 2,586 nucleotides. The deduced protein sequence encoded by pgaW has about 50% amino acid identity to several well-characterized PGAs, including those of Providencia rettgeri, Kluyvera cryocrescens, and Escherichia coli. Biochemical studies showed that the optimal temperature for this novel PGA (PGA650) activity is greater than 60°C and its half-life of inactivation at 55°C is four times longer than that of another previously reported thermostable PGA from Alcaligenes faecalis (R. M. D. Verhaert, A. M. Riemens, J. V. R. Laan, J. V. Duin, and W. J. Quax, Appl. Environ. Microbiol. 63:3412-3418, 1997). To our knowledge, this is the most thermostable PGA ever characterized. To explore the molecular basis of the higher thermostability of PGA650, homology structural modeling and amino acid composition analyses were performed. The results suggested that the increased number of buried ion pair networks, lower N and Q contents, excessive arginine residues, and remarkably high content of proline residues in the structure of PGA650 could contribute to its high thermostability. The unique characteristic of higher thermostability of this novel PGA provides some advantages for its potential application in industry.

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