Crystal structure of the complex between cyclic-di-inosine monophosphate and the Vibrio cholerae standalone phosphodiesterase (VcEAL) at 2.2 Å.

Cyclic dinucleotides (CDNs) are a significant and expanding class of secondary messengers that influence several vital bacterial physiological functions. Therefore, an understanding of the process by which CDNs are degraded by their cognate PDEs is crucial for comprehending a variety of cellular processes, such as the formation and dissemination of biofilms. As an alternative, it might be beneficial to create and/or identify non-hydrolyzable CDN derivatives to employ them as chemical probes of cyclic-di-GMP (c-di-GMP) signaling. Cyclic-di-inosine monophosphate, or c-di-IMP, is not a naturally occurring signaling molecule in biological systems, but it has strong adjuvant effects on metazoans and functions as an immunological modulator and stimulant. Here we report the first structural details of c-di-IMP and EAL interaction through high-resolution (2.2 Å) crystal structure of VcEAL in complex with c-di-IMP + Ca. Comparison of the VcEAL structures bound with cyclic-di-GMP (c-di-GMP), 3',5'-cyclic-AMP-GMP (cGAMP) and c-di-IMP and the structural variations at the chemical level between these CDNs provides their structural basis of recognition and rate of hydrolysis.