Amon, J. D. | Search bioRxiv

bioRxiv2026

Structural basis for nutrient-activated channel opening in bacterial spore germination receptors

GerA-family germinant receptors were recently identified as ion channels that initiate germination of dormant bacterial spores in response to nutrients. Here we report 2.0-[A] cryo-electron microscopy structures of apo, agonist-bound, and antagonist-bound GerA, revealing a symmetric pentamer of heterotrimers. Signaling relies on two allosteric switches that radiate from the LeuT-type ligand-binding subunit in opposite directions, one away from the channel subunit and one directly toward it. A lipoprotein subunit reroutes the first switch and allosterically activates the second, promoting their convergence on the channel. Together, these rearrangements comprise a multipronged, cooperative signal transduction pathway that connects nutrient binding to pore opening in this new class of ligand-gated ion channels.

biophysics↗

bioRxiv2021

Genetic evidence for signal transduction within the Bacillus subtilis GerA germinant receptor

Bacterial spores can rapidly exit dormancy through the process of germination. This process begins with the activation of nutrient receptors embedded in the spore membrane. The prototypical germinant receptor in Bacillus subtilis responds to L-alanine and is thought to be a complex of proteins encoded by the genes in the gerA operon: gerAA, gerAB, and gerAC. The GerAB subunit has recently been shown to function as the nutrient sensor, but beyond contributing to complex stability, no additional functions have been attributed to the other two subunits. Here, we investigate the role of GerAA. We resurrect a previously characterized allele of gerA (termed gerA*) that carries a mutation in gerAA and show it constitutively activates germination even in the presence of a wild-type copy of gerA. Using an enrichment strategy to screen for suppressors of gerA*, we identified mutations in all three gerA genes that restore a functional receptor. Characterization of two distinct gerAB suppressors revealed that one (gerAB-E105K) reduces the GerA complexs ability to respond to L-alanine, while another (gerAB-F259S) disrupts the germinant signal downstream of L-alanine recognition. These data argue against models in which GerAA is directly or indirectly involved in germinant sensing. Rather, our data suggest that GerAA is responsible for transducing the nutrient signal sensed by GerAB. While the steps downstream of gerAA have yet to be uncovered, these results validate the use of a dominant-negative genetic approach in elucidating the gerA signal transduction pathway. ImportanceEndospore formers are a broad group of bacteria that can enter dormancy upon starvation and exit dormancy upon sensing the return of nutrients. How dormant spores sense and respond to these nutrients is poorly understood. Here, we identify a key step in the signal transduction pathway that is activated after spores detect the amino acid L-alanine. We present a model that provides a more complete picture of this process that is critical for allowing dormant spores to germinate and resume growth.

microbiology↗