Molecular cloning and analysis of the gene encoding the thermostable penicillin G acylase from Alcaligenes faecalis.

The large heterodimeric penicillin G acylase from Alcaligenes faecalis was displayed on the surface of phage fd. We fused the coding sequence (α subunit-internal peptide-β subunit) to the gene of a phage coat protein. A modified g3p signal sequence was used to direct the polypeptide to the periplasm. Here we show that a heterodimeric enzyme can be expressed as a fusion protein that matures to an active biocatalyst connected to the coat protein of phage fd, resulting in a phage to which the β-subunit is covalently linked and the α-subunit is non-covalently attached. The enzyme can be displayed either fused to the minor coat protein g3p or fused to the major coat protein g8p. In both cases the penicillin G acylase on the phage has the same Michaelis constant as its freely soluble counterpart, indicating a proper folding and catalytic activity of the displayed enzyme. The display of the heterodimer on phage not only allows its further use in protein engineering but also offers the possibility of applying this technology for the excretion of the enzyme into the extracellular medium, facilitating purification of the protein. With the example of penicillin acylase the upper limit for a protein to become functionally displayed by phage fd has been further explored. Polyvalent display was not observed despite the use of genetic constructs designed for this aim. These results are discussed in relation to the pore size being formed by the g4p multimer.

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

Applied and Environmental Microbiology ◽

10.1128/aem.70.5.2764-2770.2004 ◽

2004 ◽

Vol 70 (5) ◽

pp. 2764-2770 ◽

Cited By ~ 30

Author(s):

Gang Cai ◽

Songcheng Zhu ◽

Sheng Yang ◽

Guoping Zhao ◽

Weihong Jiang

Keyword(s):

Escherichia Coli ◽

Amino Acid ◽

Molecular Basis ◽

Alcaligenes Faecalis ◽

Amino Acid Identity ◽

Penicillin G Acylase ◽

Penicillin G ◽

Achromobacter Xylosoxidans ◽

High Thermostability ◽

Arginine Residues

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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