J-protein co-chaperone system mediates selective autophagy targeting of pathogenic protein aggregates

Molecular Mechanism and Rationale

The J-protein co-chaperone system functions as a critical autophagy adapter mechanism that selectively targets pathogenic protein conformers for autophagic degradation through distinct molecular recognition and trafficking pathways. DNAJB6 and DNAJB2, in complex with HSP70 chaperones (HSPA8 and HSPA1A), operate as autophagy selectivity factors that recognize and deliver specific classes of misfolded proteins to the autophagosome formation machinery. The core hypothesis proposes that J-protein-HSP70 complexes function as molecular bridges between protein quality control recognition and autophagic clearance mechanisms.

Molecular Mechanism and Rationale

The J-protein co-chaperone system functions as a critical autophagy adapter mechanism that selectively targets pathogenic protein conformers for autophagic degradation through distinct molecular recognition and trafficking pathways. DNAJB6 and DNAJB2, in complex with HSP70 chaperones (HSPA8 and HSPA1A), operate as autophagy selectivity factors that recognize and deliver specific classes of misfolded proteins to the autophagosome formation machinery. The core hypothesis proposes that J-protein-HSP70 complexes function as molecular bridges between protein quality control recognition and autophagic clearance mechanisms.

DNAJB6 acts as a selective autophagy receptor for amyloid-like aggregates through direct interaction with LC3/GABARAP family proteins via a cryptic LC3-interacting region (LIR) motif within its S/T-rich domain. Upon binding to β-sheet-rich pathological structures, DNAJB6 undergoes conformational changes that expose this LIR motif, enabling recruitment of nascent autophagosomes. The DNAJB6-HSPA8 complex simultaneously engages with ULK1 kinase and WIPI2 to promote localized autophagosome nucleation around aggregate foci. This mechanism creates aggregate-specific autophagy initiation sites that bypass normal bulk autophagy regulation.

DNAJB2 operates through a distinct pathway involving p62/SQSTM1-mediated selective autophagy of stress granule components and soluble misfolded proteins. The DNAJB2-HSPA1A complex recognizes K63-polyubiquitin chains on stress-damaged proteins and facilitates their recruitment to p62 condensates. This process involves cooperative binding between DNAJB2's substrate-binding domain and p62's UBA domain, creating high-avidity interactions that promote phase separation and autophagosome targeting. The differential autophagy routing is regulated by mTORC1 signaling and AMPK-mediated phosphorylation of DNAJB2 at serine residues that modulate p62 binding affinity.

Preclinical Evidence

In autophagy-deficient ATG7 knockout neuronal cultures, DNAJB6 overexpression fails to clear huntingtin aggregates despite maintaining binding capacity, while restoration of ATG7 fully rescues clearance activity. DNAJB6 co-localizes with LC3-positive puncta in aggregate-bearing cells, and mutation of predicted LIR motifs abolishes both LC3 interaction and neuroprotective effects.