3 years ago

Synthesis and degradation of cAMP in Giardia lamblia : possible role and characterization of a nucleotidyl cyclase with a single cyclase-homology-domain.

Belen Jerez, Vanina Saraullo, Carlos Davio, Adolfo Zurita, Nicolas Di Siervi
Despite its importance in the regulation of growth and differentiation processes of a variety of organisms, the mechanism of synthesis and degradation of cAMP has not yet been described in Giardia lamblia In this work, we measured significant quantities of cAMP in trophozoites of G. lamblia incubated in vitro and later detected how it increases during the first hours of encystation, and how it then returns to basal levels at 24 h. Through an analysis of the genome of G. lamblia , we found sequences of three putative enzymes -one phosphodiesterase (gPDE) and two nucleotydyl cyclases (gNC1 and gNC2)- that should be responsible for the regulation of cAMP in G. lamblia Later, an RT-PCR assay confirmed that these three genes are expressed in trophozoites. The bioinformatic analysis indicated that gPDE is a transmembrane protein of 154 kDa, with a single catalytic domain in the C-terminal end; gNC1 is predicted to be a transmembrane protein of 74 kDa, with only one class III cyclase-homology-domain (CHD) at the C-terminal end; and gNC2 should be a transmembrane protein of 246 kDa, with two class III CHDs. Finally, we cloned and enriched the catalytic domain of gNC1 (gNC1cd) from bacteria. Later, we confirmed that gNC1cd has adenylyl cyclase activity. This enzymatic activity depends on the presence of Mn(2+) and Ca(2+), but no significant activity was displayed in the presence of Mg(2+) Additionally, the AC activity of gNC1cd is competitively inhibited with GTP, so it highly possible that gNC1 has guanylyl cyclase activity as well.

Publisher URL: http://doi.org/10.1042/BCJ20170590

DOI: 10.1042/BCJ20170590

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