ABSTRACT
The pathogenesis of infectious diarrheal diseases is largely attributed to enterotoxins that cause dehydration by disrupting intestinal water absorption. We investigated patterns of genetic variation in mammalian guanylate cyclase-C (GC-C), an intestinal receptor targeted by bacterially encoded heat-stable enterotoxins (STa), to determine how host species adapt in response to diarrheal infections. Our phylogenetic and functional analysis of GC-C supports long-standing evolutionary conflict with diarrheal bacteria in primates and bats, with highly variable susceptibility to STa across species. In bats, we further show that GC-C diversification has sparked compensatory mutations in the endogenous uroguanylin ligand, suggesting an unusual scenario of pathogen-driven evolution of an entire signaling axis. Together, these findings suggest that conflicts with diarrheal pathogens have had far-reaching impacts on the evolution of mammalian gut physiology.
Subject(s)
Bacterial Toxins/metabolism , Cyclic GMP-Dependent Protein Kinase Type II/metabolism , Enterotoxins/metabolism , Guanylate Cyclase/metabolism , Natriuretic Peptides/metabolism , Animals , Chiroptera , Cyclic GMP/metabolism , Cystic Fibrosis Transmembrane Conductance Regulator/metabolism , Diarrhea/microbiology , Diarrhea/pathology , Enterocytes/metabolism , Enterotoxigenic Escherichia coli/metabolism , Enterotoxigenic Escherichia coli/pathogenicity , Guanylate Cyclase/genetics , Natriuretic Peptides/genetics , Protein Binding , Receptors, Enterotoxin/genetics , Receptors, Enterotoxin/metabolism , Signal Transduction , Sodium-Hydrogen Exchangers/metabolism , Vibrio cholerae/metabolism , Vibrio cholerae/pathogenicityABSTRACT
Loquacious-PD (Loqs-PD) is required for biogenesis of many endogenous siRNAs in Drosophila In vitro, Loqs-PD enhances the rate of dsRNA cleavage by Dicer-2 and also enables processing of substrates normally refractory to cleavage. Using purified components, and Loqs-PD truncations, we provide a mechanistic basis for Loqs-PD functions. Our studies indicate that the 22 amino acids at the C terminus of Loqs-PD, including an FDF-like motif, directly interact with the Hel2 subdomain of Dicer-2's helicase domain. This interaction is RNA-independent, but we find that modulation of Dicer-2 cleavage also requires dsRNA binding by Loqs-PD. Furthermore, while the first dsRNA-binding motif of Loqs-PD is dispensable for enhancing cleavage of optimal substrates, it is essential for enhancing cleavage of suboptimal substrates. Finally, our studies define a previously unrecognized Dicer interaction interface and suggest that Loqs-PD is well positioned to recruit substrates into the helicase domain of Dicer-2.
