Department of Plant and Microbial Biology and BioTechnology Institute, University of Minnesota, Minnesota, United States
Todd A Wright
Department of Chemistry, University of California, Berkeley, Berkeley, United States
Philip J Kranzusch
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, United States; Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, United States; Parker Institute for Cancer Immunotherapy at Dana-Farber Cancer Institute, Boston, United States
Kevin W Doxzen
Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
James J Park
Department of Chemistry, University of California, Berkeley, Berkeley, United States
Department of Chemistry, University of California, Berkeley, Berkeley, United States; Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, United States; Department of Chemistry, University of Utah, Salt Lake City, United States
A newfound signaling pathway employs a GGDEF enzyme with unique activity compared to the majority of homologs associated with bacterial cyclic di-GMP signaling. This system provides a rare opportunity to study how signaling proteins natively gain distinct function. Using genetic knockouts, riboswitch reporters, and RNA-Seq, we show that GacA, the Hypr GGDEF in Geobacter sulfurreducens, specifically regulates cyclic GMP-AMP (3′,3′-cGAMP) levels in vivo to stimulate gene expression associated with metal reduction separate from electricity production. To reconcile these in vivo findings with prior in vitro results that showed GacA was promiscuous, we developed a full kinetic model combining experimental data and mathematical modeling to reveal mechanisms that contribute to in vivo specificity. A 1.4 Å-resolution crystal structure of the Geobacter Hypr GGDEF domain was determined to understand the molecular basis for those mechanisms, including key cross-dimer interactions. Together these results demonstrate that specific signaling can result from a promiscuous enzyme.
