University of Dundee

‘“Diverse PAMPS are synthesized by bacterial cGAS-like enzymes’

Event Date: 
Wednesday, March 20, 2019 - 12:30 to 13:30
Event Location: 
MSI Small Lecture Theatre
Host: 
Professor Paul Crocker FRSE
Event Speaker: 
Dr Aaron Whiteley
Institution: 
Harvard Medical School
Event Type: 
Seminar
Share

Abstract: 

 

 

Humans and bacteria synthesize cyclic dinucleotides that act as second messengers to control diverse cellular processes. Cyclic GMP–AMP (2′3′ cGAMP) is synthesized in humans by cGAS and 3′3′ cGAMP is synthesized in Vibrio cholerae by DncV. cGAS and DncV are <10% identical at the amino acid level but share remarkable structural homology and a conserved nucleotidyltransferase enzyme architecture. Here we report that cGAS / DncV-like nucleotidyltransferases (CD-NTases) comprise a large, unappreciated subfamily of structurally homologous enzymes that are present in nearly every bacterial phyla, and that many of these enzymes synthesize novel nucleotide second messengers. Bioinformatic analysis of greater than 5,600 CD-NTases demonstrated that these genes are distributed within mobile genetic elements and cluster into 8 specific clades. To determine the nucleotide product of each CD-NTase clade, we purified 66 enzymes and performed a biochemical screen. CD-NTases use both purine and pyrimidine nucleotides to synthesize an exceptionally diverse range of cyclic dinucleotides. A series of crystal structures establish CD-NTases as a structurally conserved family and reveal key contacts in the active-site lid that direct purine or pyrimidine selection. CD-NTase products are not restricted to dinucleotides and also include an unexpected class of cyclic trinucleotide compounds.

Cyclic dinucleotides have emerged as potent stimulators of the mammalian innate immune system and biochemical and cellular analysis of novel signaling nucleotides demonstrated that these molecules activate distinct host receptors. We hypothesize that the exceptional biochemical diversity of CD-NTase products may enable both pathogens and commensal microbiota to modulate their interactions of with animal and plant hosts. In addition to cGAS, humans encode at least ten CD-NTase genes, some with unknown function. Our findings will also provide a new foundation to illuminate these and other novel signaling pathways in both the host and bacteria.