A structural study has identified a moving loop that controls how some microbial rubisco enzymes join together. Binding a small molecule pulls the loop aside, allowing paired components to form a larger assembly. Comparisons across several enzymes reveal different routes to similar structures, adding detail to how protein assemblies evolved within this carbon-metabolism family.
Rubisco, an enzyme family involved in carbon metabolism, can take different shapes as smaller protein units join together. A peer-reviewed structural investigation found that a flexible loop controls this transition in some microbial examples. When a molecule binds to the enzyme, the loop moves away from a position that would otherwise obstruct another pair of protein units, allowing a larger structure to form.[1]
The team sought structural material from 14 enzymes across evolutionary branches and obtained enough soluble protein from seven. Among these, some enzymes changed from paired units into structures containing ten subunits, while others stayed paired or kept their larger arrangement regardless of binding. X-ray-based measurements and electron microscopy helped distinguish these behaviours and locate the moving region within the protein.[1]
Assembly responses differed between two microbial enzymes when selected amino acids were changed. A similar final architecture can therefore coexist with different requirements for molecule binding. The result contributes a structural account of diversity in protein evolution. Its scope is controlled experiments on this rubisco group: the study established neither greater crop yields nor a measured increase in carbon fixation from the larger assemblies.[1]
