Structural insights into higher-order assembly and function of the bacterial microcompartment protein PduA [Microbiology]

May 29th, 2014 by Pang, A., Frank, S., Brown, I., Warren, M. J., Pickersgill, R. W.

Bacterial microcompartments are large proteinaceaous assemblies that are found in the cytoplasm of some bacteria. These structures consist of proteins constituting a shell that houses a number of enzymes involved in specific metabolic processes. The 1,2-propanediol utilizing microcompartment is assembled from 7 different types of shell proteins, one of which is PduA. It is one of the more abundant components of the shell and intriguingly can form nanotubule-like structures when expressed on its own in the cytoplasm of E. coli. We propose a model that accounts for the size and appearance of these PduA structures and underpin our model using a combinatorial approach. Making strategic mutations at Lys26, Val51 and Arg79, we targeted residues predicted to be important for PduA assembly. We present the effect of the amino acid residue substitution on the phenotype of the PduA higher-order assemblies (TEM) and the crystal structure of the Lys26Asp mutant with one glycerol molecule bound to the central pore. Our results support the view that the hexamer-hexamer interactions seen in PduA crystals persists in the cytoplasmic structures and reveal the profound influence of the two key amino acids, Lys26 and Arg79, on tiling, not only in the crystal lattice but also in the bacterial cytoplasm. Understanding and controlling PduA assemblies is valuable in order to inform manipulation for synthetic biology and biotechnological applications.