Characterization of A phanizomenon ovalisporum amidinotransferase involved in cylindrospermopsin synthesis

An increasing abundance of A phanizomenon ovalisporum in water bodies from diverse world regions has been reported in the last few years, with the majority of the isolated strains producing the toxin cylindrospermopsin ( CYN ), leading to a rise in ecological and health risks. The understanding of CYN synthesis is crucial in the control of CYN production. An amidinotransferase ( AMDT ) seems to be the first enzyme involved in the synthesis of CYN . In this study, we have cloned and overexpressed the aoaA gene from the constitutive CYN producer A . ovalisporum UAM ‐ MAO . The recombinant purified AoaA was characterized, confirming that it is an l ‐arginine:glycine AMDT . It shows an optimal activity between 32 and 37°C, at pH from 8 to 9. The activity exhibits a mixed (ping‐pong/sequential) kinetic mechanism, and is inhibited by the reaction product guanidine acetate ( GAA ) in a noncompetitive manner. Mg 2+ stimulates AoaA activity while Co 2+ and Mn 2+ inhibit it. AoaA conserves the critical residues of the catalytic site and substrate specificity of AMDT s, as the previously reported AMDT from C ylindrospermopsis raciborskii Cyr. Both proteins can be included in a new group of prokaryotic AMDT s involved in CYN production.