Linking the Salmonella enterica 1,2-Propanediol Utilization Bacterial Microcompartment Shell to the Enzymatic Core via the Shell Protein PduB

Abstract

MCPs are unique, genetically encoded organelles used by many bacteria to survive in resource-limited environments. There is significant interest in understanding the biogenesis and function of these organelles, both as potential antibiotic targets in enteric pathogens and also as useful tools for overcoming metabolic engineering bottlenecks.

In Vitro Analysis of Bacterial Microcompartments and Shell Protein Superstructures by Confocal Microscopy

“…Together, these data tentatively support interactions between EPs and the N terminus of PduB and between EPs and PduA. These data are consistent with the hypothesis that PduB ( 38 , 39 ) and PduA are likely to be primary factors in facilitating shell-cargo interactions.…”

Kinetic Growth of Multicomponent Microcompartment Shells

“…This establishes a baseline that we can then compare to the behavior of multicomponent shells. This understanding also helps us to select components that replicate behavior seen in experiment such as PduB being responsible for assembly on a phase separated cargo globule . Assembly of a single shell protein is characterized by only two parameters, the shell-cargo interaction, U SC , and the shell–shell interaction, U SS (Figure (d)).…”

“…Cargo–cargo interactions are always set to a value such that the cargo spontaneously phase separates (Figure (b)) into a liquid droplet. The segregation of cargo has been shown in the Pdu microcompartment system …”

“…Recent experimental results for the Pdu MCP system highlight the need for this type of analysis. Specifically, the deletion of one minority shell protein, PduB (see Figure (a) and (b)), causes the MCP to form empty shells that do not assemble around enzymatic cargo. − To accurately describe how removal of specific hexamers changes the assembly pathway, , models must contain multiple different types of shell proteins. Here, we include three different types of coarse-grained hexameric shell proteins shown in Figure (c) and (d) and a phase separated cargo.…”

“…Core-first assembly can be further divided into en masse assembly, where many shell proteins bind the template and then anneal into a final structure, and assembly via elongation where a nucleus of shell proteins is formed on the template followed by growth one shell protein at a time into a full, closed shell . However, experiments , have led to the idea that cargo-encapsulating shells may be nucleating separately from the enzyme cargo and thus the shell assembly is bulk-nucleated instead of cargo-nucleated. The coarse-grained model explored in this work with three shell protein components describes this scenario.…”