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

Protein homeostasis (proteostasis) deficiency is recognized as a contributing factor to many neurodegenerative, neurological, and metabolic diseases. However, how the proteostasis network orchestrates the folding and assembly of multi-subunit membrane proteins is not completely understood. In this investigation, we focus on characterizing the biogenesis pathway of a multi-subunit neuroreceptor, the gamma-aminobutyric acid type A (GABAA) receptor. Previous proteomics studies identified Hsp47 (Gene: SERPINH1), a heat shock protein in the endoplasmic reticulum lumen, as the most enriched GABAA receptor-interacting chaperone. Here, we show that Hsp47 enhances neuronal GABAA receptor functional surface expression, acting after Binding immunoglobulin Protein (BiP), to preferentially bind the folded conformation of GABAA receptors. Therefore, Hsp47 promotes the subunit-subunit interaction, the receptor assembly process, and the anterograde trafficking of GABAA 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. ### Competing Interest Statement The authors have declared no competing interest.