Molecular Machines

Proteins are fundamentally important to life, since they perform all of functions within living organisms. It is the protein’s structure that defines its biological function within a cell, however, protein function is a dynamical process. Therefore, to understand completely how a protein functions, we must also understand how it moves.

Using single molecule measurements of proteins, it is possible to directly observe and manipulate protein motions, and to study how they are influenced by interactions with other molecules. From such experiments, the rates of folding, unfolding, association and dissociation as well as stabilities of the proteins under different conditions can also be found.

The experimental systems used in the lab, custom-built dual-beam optical traps, provide sub-nanometre spatial and pico-Newton force resolution. Using this setup, in combination with biochemical functional assays, molecular machines are studied in detail.

Molecular chaperones are essential proteins for cell viability, which assist in the folding, unfolding, assembly and disassembly of their client proteins. They can also maintain protein stability under conditions of stress. Several different chaperones are studied in the Rief group.

Heat shock protein 90 (Hsp90) is a molecular chaperone which is one of the most abundant proteins found in eukaryotic cells. Its abundance underlines its importance, as it is known to be involved in the assembly and regulation of cellular signalling systems which, in turn, ensure that cell growth is regulated.

The open and closed conformations of Hsp90 from crystal structures (PDB accession codes: 2CG9 and 2IOQ)

Heat shock protein 70 (Hsp70) is another important class of molecular chaperones. They assist in a variety of cellular process, including the folding of nascent polypeptide chains, assembly of protein complexes and the control of the biological activity of folded proteins.

E.coli Hsp70: DnaK structure from NMR (PDB accession code: 2KHO)