In molecular self-assembly, molecules or parts of molecules spontaneously form ordered structures. Macromolecular assemblies consist of multiple proteins and often contain other molecules such as DNA, RNA, sugars and/or lipids. The assembly of macromolecular complexes in a cell is a highly regulated, multistep process.
Mass photometry characterises these complex particles with efficiency and accuracy, enabling the engineering of new supramolecular structures with great potential for medical research.
GroEL belongs to the family of chaperonins and thus assists in the correct folding and assembly of other proteins in the cell. It consists of 14 monomers forming a cage-like structure. Mass photometry can monitor formation of this complex in the absence or presence of ATP (Figure).
Ribosomes are macromolecular assemblies of protein and RNA, and are central sites for protein synthesis. Bacterial ribosomes (in this example from E. coli) are >2 MDa in size. Magnesium ions play a subtle yet important role in the assembly of intact (70S) complexes. In the absence of magnesium, E. coli ribosomes rapidly disassemble into their 30S and 50S subunits. Mass photometry allows us to monitor these processes (Figure).
An ultra-stable gold-coordinated protein cage displaying reversible assembly
Malay at al., Nature 2019, 569(7756), 438-442
Cage-like protein assemblies have potential uses in medicine, including as vaccines and in drug delivery. In this study, mass photometry was used to follow formation of a TRAP-cage. It showed that a critical concentration of TRAP is required for effective cage formation. Above this critical concentration, the TRAP rings appear to rapidly assemble into an intermediate, partially formed cage, with the cage then forming from this intermediate.