A Major Shell Protein of 1,2-Propanediol Utilization Microcompartment Conserves the Activity of Its Signature Enzyme at Higher Temperatures

A classic example of an all-protein natural nano-bioreactor, the bacterial microcompartment is a prokaryotic organelle that confines enzymes in a small volume enveloped by an outer protein shell. These protein compartments metabolize specific organic molecules, allowing bacteria to survive in restricted nutrient environments. In this work, 1,2-propanediol utilization microcompartment (PduMCP) was used as a model to study the effect of molecular confinement on the stability and catalytic activity of native enzymes in the microcompartment. A combination of enzyme assays, spectroscopic techniques, binding assays, and computational analysis were used to evaluate the impact of the major shell protein PduBB ' on the stability and activity of PduMCP ' s signature enzyme, dioldehydratase PduCDE. While free PduCDE shows similar to 45 % reduction in its optimum activity (activity at 37 degrees C) when exposed to a temperature of 45 degrees C, it retains similar activity up to 50 degrees C when encapsulated within PduMCP. PduBB ', a major component of the outer shell of PduMCP, preserves the catalytic efficiency of PduCDE under thermal stress and prevents temperature-induced unfolding and aggregation of PduCDE in vitro. We observed that while both PduB and PduB ' interact with the enzyme with micromolar affinity, only the PduBB ' combination influences its activity and stability, highlighting the importance of the unique PduBB ' combination in the functioning of PduMCP.

Automated summary

The bacterial microcompartment is a prokaryotic organelle that confines enzymes in a small volume enveloped by an outer protein shell. This study found that the major shell protein PduBB' preserves the catalytic activity and stability of enzymes within the microcompartment, preventing unfolding and aggregation under thermal stress.