Dynamic chaperone–client-interactions characterized at atomic resolution

Molecular chaperones are essential in cellular protein homeostasis. Central mechanistic aspects of chaperone function are not well understood at the atomic level, including how chaperones recognize clients, in which conformational states clients are bound, and how chaperone–client interactions are integrated into functional cycles. Solution NMR spectroscopy is the only method to resolve dynamic chaperone–client interactions at atomic resolution, giving us enormous potential to address these questions. Our initial work on the homotrimeric holdase chaperone Skp with bound outer membrane proteins provided the first atomic-level description of a natural full-length chaperone­­–client complex [1, 2]. Subsequent work showed how periplasmic chaperones shape individual client folding trajectories at the membrane bilayer [3]. We now find that the monomeric state of the chaperone Skp is intrinsically disordered, and that oligomerization initiates folding via a “stapling” mechanism. This coupled oligomerization, folding and client-binding mechanism is a unique mechanistic example of how an ATP-independent chaperone can modulate its activity.
An atomic-resolution characterization of the Spy–Im7 model system revealed general principles how Spy and other chaperones selectively recognize the flexible, locally frustrated regions of partially folded clients [4,5]. These mechanistic insights were fruitfully used to investigate the functional role of chaperones in Parkinson’s disease. Parkinson’s disease is a common neurodegenerative disorder manifested by intracellular aggregates of the intrinsically disordered protein α-Synuclein. Systematic investigations identified a general chaperone interaction motif at the α-Synuclein amino-terminus. A dominant regulatory role of chaperones on cytosolic α-Synuclein was validated with in-cell NMR spectroscopy and the functional basis for the effects of known post-translational modifications could be reconstituted. The data reveal how molecular chaperones control the state of intracellular α-Synuclein and how the disturbance of these interactions leads to progress of pathologically relevant aggregates.

Written by .S. Hiller¹, B. M. Burmann¹, G. Mas¹, R. Riek², J. A. Gerez^{2 -
1}Biozentrum, University of Basel, 4056 Basel, Switzerland.
²Laboratory of Physical Chemitrsy, ETH Zürich, 8093 Zurich, Switzerland.