The research group of Prof.
Chen Yuxing and Prof.
Zhou Congzhao of our hospital analyzed the three-dimensional structure of the complex of human cholesterol efflux transporter ABCG1 and its substrates cholesterol, ATP and sphingomyelin with a resolution of about 3.
3 Å using single-particle cryo-electron microscopy .
A series of structure-based biochemical and cell biology studies revealed the molecular mechanism of cholesterol efflux across membranes via ABCG1 , and found that cholesterol receptors and membrane sphingomyelin molecules are required for efflux activity .
The related research results were published online in Cell Reports on January 25 , 2022 under the title of " Structure and Transport Mechanism of the Human Cholesterol Transporter ABCG1 " .
Cholesterol, as a major component of the plasma membrane of mammalian cells , plays a key role in maintaining membrane fluidity and stability and in the synthesis of bile acids, steroid hormones, and vitamin D
and other metabolic processes .
Excess intracellular cholesterol can be transferred from peripheral tissue cells to the liver via the reverse cholesterol transport (RCT)
When RCT functions abnormally, intracellular cholesterol will accumulate excessively, eventually leading to atherosclerosis, which is currently the number one fatal disease in the world
As a key membrane protein in the RCT pathway, ABCG1 is responsible for transporting cholesterol to the outside of the cell, and its abnormal function is highly correlated with major diseases such as atherosclerosis .
Figure 1 Three-dimensional structure of ABCG1 and its molecular mechanism of cholesterol transport
This paper reports a three-dimensional structure of ABCG1 with an open-to-intracellular conformation
Due to the simultaneous binding of ATP and substrate molecules, the structure is in an intermediate state of alternating conformational changes
Based on structural analysis, biochemical and cell biology experiments, the authors identified the amino acid residues of ABCG1 that bind cholesterol substrates, elucidate the protein - substrate interaction mode, and found a group of amphetamines at the exit of the substrate-binding pocket Acid residues are very important for substrate transport
Corresponding biochemical experiments revealed that ABCG1 activity is also dependent on the cholesterol receptor, high-density lipoprotein HDL
The researchers also used mass spectrometry to identify sphingomyelin components that bind specifically near the protein substrate-binding pocket
Structural analysis and functional experiments revealed that this sphingomyelin molecule is required for ABCG1 -mediated cholesterol transport
Based on the above experimental results, the authors propose a model for the mechanism of ABCG1 -mediated cholesterol efflux: sphingomyelin assists cholesterol binding to ABCG1 and participates in the formation of a complete binding pocket to stabilize substrate molecules, and extracellularly bound HDL promotes cholesterol from ABCG1 substrates Pockets in the outer row (Figure 1 )
The study revealed not only the interaction mode of ABCG1 with cholesterol but also HDLThe importance of cholesterol efflux transport has further improved the regulatory network of cholesterol metabolism, which has important theoretical guiding significance for the prevention and treatment of diseases related to cholesterol metabolism disorders
Professor Chen Yuxing, Professor Zhou Congzhao and Hou Wentao are the co-corresponding authors of the paper, and Dr.
Xu Da is the first author of the paper
Cryo-EM data collection was completed at the Bioimaging Center of the University of Science and Technology of China
The research work was greatly assisted by Researcher Li Yanyan from the School of Life Sciences of West Lake University, Professor Yao Xuebiao and Dr.
Yang Fengrui from the Key Laboratory of Membraneless Organelles and Cell Dynamics of the Ministry of Education, University of Science and Technology of China, and received funding from the Ministry of Science and Technology and the National Natural Science Foundation of China.
and funding from the Chinese Academy of Sciences
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