Hsp47 Promotes Biogenesis of Multi-subunit Neuroreceptors in the Endoplasmic Reticulum

Protein homeostasis (proteostasis) deficiency is an important contributing factor to neurodegenerative, neurological, and metabolic diseases. However, how the proteostasis network orchestrates the folding and assembly of multi-subunit membrane proteins is not well understood. Previous proteomics studies identified Hsp47 (Gene: SERPINH1 ), a heat shock protein in the endoplasmic reticulum lumen, as the most enriched interacting chaperone for gamma-aminobutyric type A (GABA _A ) receptors. Here, we show that Hsp47 enhances neuronal GABA _A receptor functional surface expression, acting after Binding immunoglobulin Protein (BiP) to preferentially bind the folded conformation of GABA _A receptors. Therefore, Hsp47 promotes the subunit-subunit interaction, the receptor assembly process, and the anterograde trafficking of GABA _A receptors. These Hsp47 properties are also extended to other Cys-loop receptors, including nicotinic acetylcholine receptors. Therefore, in addition to its known function as a collagen chaperone, this work establishes that Hsp47 also plays a critical and general role in the maturation of multi-subunit neuroreceptors.