Isethionate sulfite-lyase (IslA) is a glycyl radical enzyme that catalyzes the degradation of isethionate into acetaldehyde and sulfite through the cleavage of a C-S bond. This conversion is a necessary step within taurine catabolism in anaerobic bacteria like Bilophila wadsworthia. IslA is activated by the its activating enzyme IslB which uses S-adenoslymethionine (SAM) as the initial radical donor. Structure IslA, like all other characterized glycyl radical enzymes, is a dimeric protein. The monomer of IslA contains a barrel consisting of an alpha helix than envelopes two five-stranded half-beta barrels positioned antiparallel to each other. Hidden within this barrel is the active site of the enzyme. It is believed that the positioning of the active site within the barrel protects the radical species (formed during the activation of the enzyme) from solvent quenching. Bacterial microcompartments Within the same gene cluster that encodes IslA and IslB enzymes are several genes that encode shell proteins of bacterial microcompartments (BMCs). It has been found that the IslA and IslB enzymes are likely contained within BMCs which isolate the products of IslA (acetaldehyde and sulfite) from the cytosol. It is believed that isolating these products from the cytosol, the bacteria is able to limit their harmful effects. The flavin molecules, which are also present in the BMCs, may be used to shuttle electrons to the IslB enzyme which is necessary to install the glycyl radical on the IslA enzyme upon activation. References Lyases