1. Structural insights into the activation of autoinhibited human lipid flippase ATP8B1 upon substrate binding.
- Author
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Meng-Ting Cheng, Yu Chen, Zhi-Peng Chen, Xin Liu, Zhiyong Zhang, Yuxing Chen, Wen-Tao Hou, and Cong-Zhao Zhou
- Subjects
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MEMBRANE lipids , *BILE acids , *LIPIDS , *ADENOSINE triphosphatase , *PHOSPHATIDYLSERINES , *COMMERCIAL products - Abstract
The human P4 ATPase ATP8B1 in complex with the auxiliary noncatalytic protein CDC50A or CDC50B mediates the transport of cell-membrane lipids from the outer to the inner membrane leaflet, which is crucial to maintain the asymmetry of membrane lipids. Its dysfunction usually leads to an imbalance of bile-acid circulation and eventually causes intrahepatic cholestasis diseases. Here, we found that both ATP8B1-CDC50A and ATP8B1-CDC50B possess a higher ATPase activity in the presence of the most favored substrate phosphatidylserine (PS), and, moreover, that the PS-stimulated activity could be augmented upon the addition of bile acids. The 3.4-Å cryo-electron microscopy structures of ATP8B1-CDC50A and ATP8B1-CDC50B enabled us to capture a phosphorylated and autoinhibited state, with the N- and C-terminal tails separately inserted into the cytoplasmic interdomain clefts of ATP8B1. The PS-bound ATP8B1-CDC50A structure at 4.0-Å resolution indicated that the autoinhibited state could be released upon PS binding. Structural analysis combined with mutagenesis revealed the residues that determine the substrate specificity and a unique positively charged loop in the phosphorylated domain of ATP8B1 for the recruitment of bile acids. Together, we supplemented the Post-Albers transport cycle of P4 ATPases with an extra autoinhibited state of ATP8B1, which could be activated upon substrate binding. These findings not only provide structural insights into the ATP8B1-mediated restoration of human membrane lipid asymmetry during bile-acid circulation, but also advance our understanding of the molecular mechanism of P4 ATPases. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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