Structural analysis of the protein shell of the propanediol utilisation metabolosome
Abstract
Propanediol metabolism occurs within a proteinaceous organelle in several bacterial
species including Citrobacter freundii and Lactobacillus reuteri. The propanediol
utilisation (Pdu) microcompartment shell is built from thousands of hexagonal
shaped protein oligomers made from seven different types of protein subunits. In
this Thesis, I investigate and analyse the structure and assembly of the bacterial
microcompartment shell proteins.
One of the shell proteins characterised in this work, PduT, has a tandem canonical
bacterial microcompartment (BMC) repeat within the subunit and forms trimers with
pseudo-hexagonal symmetry. This trimeric assembly forms a flat approximately
hexagonally shaped disc with a central pore that is suitable for binding a 4Fe-4S
cluster. The essentially cubic shaped 4Fe-4S cluster conforms to the threefold
symmetry of the trimer with one free iron, the role of which could be to supply
electrons to an associated microcompartment enzyme, PduS.
The major shell protein PduB has a tandem permuted BMC repeat within the subunit
and also forms trimers with pseudo-hexagonal symmetry. This shell protein closely
resembles its homologous counterpart, EtuB; both possess three small pores formed
within the subunits rather than a single pore at the centre of the pseudo-hexameric
disc. The crystal structure of PduB provides insights into how substrates such as
glycerol are able to use these pores as substrate channels. PduB appears to be able to
pack within a sheet of PduA molecules, suggesting how the facet of the shell may be
assembled.
The higher order packing of shell proteins was investigated using PduA. Residues
important for the packing of molecules into sheets were mutated and the effects on
crystal morphology and on the shape of structures formed within the bacterial cell
were assessed. PduA appears to assemble into straws in the bacterial cell and
mutation of these residues has a profound influence on the structures produced.
Authors
Pang, AllanCollections
- Theses [3834]