Scientists in the UK have proposed a mechanism to explain how bacterial proteins act as 'molecular chaperones', proteins that assist in the folding of other proteins into their 3D structures.

Andrew Miller and colleagues at Imperial College London studied the interactions of GroEL and GroES, Escherichia coli chaperone proteins, with a model protein called zinc-cytochrome c. They found that the refolding of zinc-cytochrome c was slower when the chaperones were present. 

Miller suggests that the GroEL and GroES proteins play a thermodynamic role in controlling the rate of correct protein folding. He proposed that the two chaperone proteins help to prevent aggregation of partially folded intermediates by a mechanism called 'passive kinetic partitioning'. In this mechanism a chaperone protein binds the intermediates then releases them in a controlled way. The chaperone stops the intermediates forming clusters by keeping them at low concentrations.

Despite the fact that a protein's 3D structure is predetermined by its core amino acid sequence, proteins often need assistance to fold/refold - hence molecular chaperones are common in all organisms. GroEL and GroES are particularly remarkable, because they assist the folding/refolding of many different proteins, said Miller. A number of scientists are now trying to determine the exact function of these chaperones. 

'The passive kinetic partitioning mechanism should be adopted as the cleanest and simplest way to characterise the core function of the GroEL/GroES molecular chaperone,' said Miller.

Katherine Vickers