Dr. Jon Marles-Wright, Institute of Structural and Molecular Biology, School of Biological Sciences, University of Edinburgh.
Wednesday 13th May, 1.00 p.m., Stacey Lecture Theatre 1
Encapsulins are a class of metabolic compartments that are widely distributed in bacterial and archaeal lineages. These compartments sequester enzymes with peroxidase activity within their central cavity and protect their host cell from oxidative damage resulting from the activity of these enzymes. The encapsulin shell is formed by a protein that is resembles a virus capsid protein and appears to be a case of a genomically integrated bacteriophage that has become defective for replication which has been put to use by its host. The enzymes within encapsulins fall into two classes: dye dependent peroxidases; and ferritin-like proteins. The dye dependent peroxidase enzymes are a well characterised family of heme-dependent enzymes that have a radical mechanism of action and are able to degrade ado-dyes. The ferritin-like proteins found in encapsulins represent a new class of this family of iron-oxidising enzymes. We have determined the X-ray crystal structure of the encapsulated ferritin from the Rhodococcus Jostii encapsulin. This protein has a half-ferritin sequence motif and forms a ‘ring-donut’ structure with the active site formed by two protein chains. This arrangement is starkly different to the classical ferritin cage and has consequences for its role in iron storage. By encapsulating this ferritin within a large capsid, bacteria and archaea are able to store ten times as much iron within its cage in comparison to the classical ferritins.