Fig. 4: Binding and degradation of SAM-AMP by ancillary CRISPR proteins.
From: Antiviral type III CRISPR signalling via conjugation of ATP and SAM
a, CorA binds SAM-AMP and SAH-AMP, but not cA3 (1 µM 32P-labelled ligand incubated with 0, 0.0625, 0.125, 0.35, 0.75, 1.5 and 3.3 µM CorA), illustrated by acrylamide gel electrophoresis and phosphorimaging. Uncropped gels are shown in Supplementary Data Fig. 4. b, Two views of the predicted structure of the pentameric CorA channel, with one subunit coloured green. c, NrN specifically degrades SAM-AMP to SAM and AMP. HPLC analysis of samples in which purified SAM-AMP was incubated with NrN and NrNΔ, an inactive variant with D85A/H86A/H87A mutations. C. botulinum lyase degrades SAM-AMP to generate MTA and l-homoserine lactone (not UV visible). Small amounts of MTA are present in the SAM-AMP sample purified from E. coli. Uncropped HPLC traces are available in Supplementary Data Fig. 4. d, Schematic representation of the reactions catalysed by NrN and SAM-AMP lyase.
