MCDB Seminar: Dannie Durand (Carnegie-Mellon) “Evolutionary remodeling of a bacterial signaling pathway”
October 18, 2023
12:00 PM - 1:00 PM
Dannie Durand is Associate Professor at the Departments of Biological Sciences and Computational Biology at Carnegie Mellon University. Kevin Drew is the event host.
Abstract:
Survival in a changing world requires flexible signaling circuitry that can evolve to sense new environmental challenges. The Firmicute sporulation initiation (Spo0) pathway is a compelling example of pathway remodeling over the course of evolution. In Clostridium acetobutylicum, a sensor kinase directly activates the master regulator of sporulation, Spo0A. In Bacillus subtilis, Spo0A is activated indirectly via a four-protein phosphorelay. These observations led to the widely accepted hypothesis that the ancestral Spo0 pathway in the earliest spore-former had the simpler, two-protein architecture; the four-protein Spo0 phosphorelay arose later in Bacilli via gain of additional proteins and interactions.
In an analysis of 84 Firmicutes genomes, we were surprised to discover phosphorelay proteins not only in Bacilli, but also in many Clostridia. This is consistent with a different model wherein the ancestral pathway was a four-protein phosphorelay and the simpler direct phosphorylation architecture is a derived state. This model is further supported by in vitro phosphotransfer experiments in which replacing any Bacillar phosphorelay protein with the corresponding protein from a Clostridial phosphorelay results in a functional pathway. Thus, the interaction specificity of Spo0 phosphorelay proteins has not changed since their divergence from the ancestral phosphorelay over 2.7 BYA. Finally, the phylogenetic distribution of Clostridial direct phosphorylation Spo0 pathways is patchy. This suggests multiple, independent instances of remodeling from phosphorelay to direct phosphorylation by acquisition of a kinase capable of phosphorylating the master regulator (Spo0A) directly. We conclude that the combined effects of a flexible encoding of interaction specificity, a phenotype that is only intermittently essential, and the recruitment of kinases to recognize novel environmental signals resulted in repeated evolution of a simpler pathway.
Date posted
Sep 27, 2023
Date updated
Sep 29, 2023