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Publication Abstract from PubMed

Cyclic di-AMP (c-di-AMP) is a relatively new member of the family of bacterial cyclic dinucleotide second messengers. It has attracted significant attention in recent years because of the abundant roles it plays in a variety of Gram-positive bacteria. The structural features that allow diverse bacterial proteins to bind c-di-AMP are not fully understood. Here we report the biophysical and structural studies of c-di-AMP in complex with a bacterial cation-proton antiporter (CpaA) RCK (regulator of the conductance of K(+)) protein from Staphylococcus aureus (Sa). The crystal structure of the SaCpaA_RCK C-terminal domain (CTD) in complex with c-di-AMP was determined to a resolution of 1.81 A. This structure revealed two well-liganded water molecules, each interacting with one of the adenine bases by a unique H2Olp-pi interaction to stabilize the complex. Sequence blasting using the SaCpaA_RCK primary sequence against the bacterial genome database returned many CpaA analogues, and alignment of these sequences revealed that the active site residues are all well-conserved, indicating a universal c-di-AMP binding mode for CpaA_RCK. A proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. A comparison of this structure to all other reported c-di-AMP-receptor complex structures revealed that c-di-AMP binds to receptors in either a "U-shape" or "V-shape" mode. The two adenine rings are stabilized in the inner interaction zone by a variety of CH-pi, cation-pi, backbone-pi, or H2Olp-pi interaction, but more commonly in the outer interaction zone by hydrophobic CH-pi or pi-pi interaction. The structures determined to date provide an understanding of the mechanisms by which a single c-di-AMP can interact with a variety of receptor proteins, and how c-di-AMP binds receptor proteins in a special way different from that of c-di-GMP.

Structural Insights into the Distinct Binding Mode of Cyclic Di-AMP with SaCpaA_RCK.,Chin KH, Liang JM, Yang JG, Shih MS, Tu ZL, Wang YC, Sun XH, Hu NJ, Liang ZX, Dow JM, Ryan RP, Chou SH Biochemistry. 2015 Aug 11;54(31):4936-51. doi: 10.1021/acs.biochem.5b00633. Epub , 2015 Jul 27. PMID:26171638^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.