The <i>Leptospira interrogans</i> CdaA protein is a functional diadenylate cyclase

Leptospirosis is a zoonotic disease that affects humans, companion animals, livestock, and wildlife. There are over 60 species that are established pathogens. Leptospires must rapidly adapt to changing environmental conditions as they pass between the environment and vertebrates. Bioinformatic analyses have identified a putative CdaA-type diadenylate cyclase (DAC) in <i>Leptospira interrogans</i> Fiocruz L1-130 (<i>lic10844</i>). DACs catalyze the synthesis of cyclic di-adenosine monophosphate (c-di-AMP) from two ATP molecules. The potential regulatory roles and effector mechanisms of c-di-AMP among pathogenic <i>Leptospira</i> species have not been explored. Here, we demonstrate that <i>lic10844</i> encodes a functional DAC (henceforth referred to as CdaA). Cellular localization analyses, size exclusion chromatography, and DAC assays revealed that CdaA is an inner membrane-associated protein that functions biologically as a homodimer, utilizing cobalt or manganese for enzymatic activity. Transcription of <i>cdaA</i> is responsive to and elevated by potassium levels. Individual amino acid residues that directly or indirectly mediate the DAC activity of CdaA were identified using site-directed mutagenesis. This report represents an important initial step in elucidating the biological function of CdaA, and by extension, c-di-AMP, in the biology and pathogenesis of <i>Leptospira</i> species.