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Ala160 and His116 residues are involved in activity and specificity of apyrase, an ATP-hydrolysing enzyme produced by enteroinvasive Escherichia coli

¹ Dipartimento di Scienze di Sanità Pubblica, Università di Roma ‘La Sapienza’, Piazzale A. Moro, 5 00185 Rome, Italy
² Dipartimento di Scienze Biomediche, Sezione di Microbiologia, Università G. D'Annunzio, Chieti, Italy
³ Dipartimento di Medicina Sperimentale, Seconda Università, Naples, Italy

Correspondence
Francesca Berlutti
francesca.berlutti{at}uniroma1.it

The virulence plasmid-carried apy (phoN2) gene of Shigella and related enteroinvasive Escherichia coli (EIEC) encodes apyrase, an ATP-diphosphohydrolase belonging to class A of the non-specific acid phosphatases (A-NSAPs). Apyrase and A-NSAPs share three domains of conserved amino acids (domains D1–D3) containing residues forming the putative active site of apyrase. In spite of their similarity, apyrase and A-NSAPs show different substrate specificity, apyrase being able to hydrolyse nucleotide tri- and diphosphates, but not monophosphates, as well as p-nitrophenyl phosphate (pNPP), while A-NSAPs are also active towards monophosphates and pNPP. In this paper, to get further insights into the structure–function relationship of apyrase, a random and site-directed mutagenesis of the apy gene of EIEC strain HN280 was conducted. Results indicate that amino acids located within the D2 and D3 conserved domains (Ser157 and Arg192, respectively) as well as residues located in the N-terminal (Ser97) and C-terminal (Glu233) domains are required for enzyme activity. Surprisingly, Ala160, located near the D2 domain and considered to be important for enzyme specificity, is required for enzyme activity, as its substitution with Thr led to the inactivation of enzyme activity. Furthermore, residue His116 is involved in apyrase specificity, since the H116L apyrase mutant shows substrate specificity resembling that of A-NSAPs.

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				D. Santapaola, F. Del Chierico, A. Petrucca, S. Uzzau, M. Casalino, B. Colonna, R. Sessa, F. Berlutti, and M. Nicoletti Apyrase, the Product of the Virulence Plasmid-Encoded phoN2 (apy) Gene of Shigella flexneri, Is Necessary for Proper Unipolar IcsA Localization and for Efficient Intercellular Spread J. Bacteriol., February 15, 2006; 188(4): 1620 - 1627. [Abstract] [Full Text] [PDF]