Transport mechanism of human bilirubin transporter ABCC2 tuned by the inter-module regulatory domain

• Published in: Nature communications 2024-02, Vol.15 (1), p.1061-12, Article 1061
• Main Authors: Mao, Yao-Xu, Chen, Zhi-Peng, Wang, Liang, Wang, Jie, Zhou, Cong-Zhao, Hou, Wen-Tao, Chen, Yuxing
• Format: Article
• Language: English
• Subjects: 101/28; 631/45/612/1237; 631/535/1258/1259; 631/57/2283; 692/699/317; 82/83; ABC transporter; Adenosine diphosphate; Adenosine Triphosphate - metabolism; Affinity; ATP-Binding Cassette Transporters - metabolism; Bile ducts; Bilirubin; Binding; Cryoelectron Microscopy; Docks; Dubin-Johnson syndrome; Electron microscopy; Erythrocytes; Hepatocytes; Humanities and Social Sciences; Humans; Jaundice; Life span; Liver diseases; Membrane Transport Proteins; Modules; multidisciplinary; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins - genetics; Multidrug Resistance-Associated Proteins - metabolism; Science; Science (multidisciplinary); Structural analysis; Substrate specificity; Substrates; Translocation
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-45337-5

Bilirubin is mainly generated from the breakdown of heme when red blood cells reach the end of their lifespan. Accumulation of bilirubin in human body usually leads to various disorders, including jaundice and liver disease. Bilirubin is conjugated in hepatocytes and excreted to bile duct via the ATP-binding cassette transporter ABCC2, dysfunction of which would lead to Dubin-Johnson syndrome. Here we determine the structures of ABCC2 in the apo, substrate-bound and ATP/ADP-bound forms using the cryo-electron microscopy, exhibiting a full transporter with a regulatory (R) domain inserted between the two half modules. Combined with substrate-stimulated ATPase and transport activity assays, structural analysis enables us to figure out transport cycle of ABCC2 with the R domain adopting various conformations. At the rest state, the R domain binding to the translocation cavity functions as an affinity filter that allows the substrates of high affinity to be transported in priority. Upon substrate binding, the R domain is expelled from the cavity and docks to the lateral of transmembrane domain following ATP hydrolysis. Our findings provide structural insights into a transport mechanism of ABC transporters finely tuned by the R domain. Human ABC transporter ABCC2 transports conjugated bilirubin from hepatocyte to bile duct, dysfunction of which causes Dubin-Johnson syndrome. Here, the authors provide structural insights into the substrate specificity of ABCC2 and the transport mechanism regulated by the R domain.