Phase separation reshapes the conformational energy landscape of a chaperone to prime its activity

Proteins adopt various conformations influenced by their cellular surroundings. Among these, biomolecular condensates play a significant role. These condensates concentrate macromolecules, generating non-membrane-enclosed compartments with distinct physicochemical properties. However, the impact of this unique solvent environment on protein structure and dynamics, and consequently their functions, remains unclear due to the challenges in conducting atomic-resolution studies in such high macromolecular content, viscous conditions.

DNAJB1, a class B co-chaperone, is of particular interest as its activity is regulated by a conformational switch. This protein recruits HSP70, a chaperone, to stress granules, enhancing its ATPase activity and promoting disassembly of these granules. To understand the changes in DNAJB1's structure and dynamics within condensates, researchers employed solution NMR spectroscopy. This technique allowed them to observe how DNAJB1's structure transforms within condensates formed by stress-granule proteins.

Upon entering the condensed phase, interactions that maintain DNAJB1 in its closed, autoinhibited state are weakened. This leads to a significant increase in s-ms dynamics (slow motion shear dynamics) and a shift towards an open, HSP70 binding-competent state, which is otherwise sparsely populated. Consequently, DNAJB1, when recruited by condensates, becomes primed for HSP70 binding.

This priming enables DNAJB1 to facilitate HSP70-mediated disassembly of reconstituted condensates and stress granules, even when the typical canonical activation mechanism for DNAJB1 is not functioning. The study concludes that condensates function as conformational regulators, reshaping protein energy landscapes to fine-tune various biochemical processes.