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Articles by Lijun Chen
Total Records ( 2 ) for Lijun Chen
  Lijun Chen , Ke Wang , Youming Shao , Jin Huang , Xiaofeng Li , Jufang Shan , Dianqing Wu and Jie J. Zheng
  Dickkopf (Dkk) proteins are antagonists of the canonical Wnt signaling pathway and are crucial for embryonic cell fate and bone formation. Wnt antagonism of Dkk requires the binding of the C-terminal cysteine-rich domain of Dkk to the Wnt coreceptor, LRP5/6. However, the structural basis of the interaction between Dkk and low density lipoprotein receptor-related protein (LRP) 5/6 is unknown. In this study, we examined the structure of the Dkk functional domain and elucidated its interactions with LRP5/6. Using NMR spectroscopy, we determined the solution structure of the C-terminal cysteine-rich domain of mouse Dkk2 (Dkk2C). Then, guided by mutagenesis studies, we docked Dkk2C to the YWTD β-propeller domains of LRP5/6 and showed that the ligand binding site of the third LRP5/6 β-propeller domain matches Dkk2C best, suggesting that this domain binds to Dkk2C with higher affinity. Such differential binding affinity is likely to play an essential role in Dkk function in the canonical Wnt pathway.
  Ke Wang , Yazhou Zhang , Xiaofeng Li , Lijun Chen , He Wang , Jianguo Wu , Jie Zheng and Dianqing Wu
  Wnt signaling is involved in a wide range of developmental, physiological, and pathophysiological processes and is negatively regulated by Dickkopf1 (Dkk1). Dkk1 has been shown to bind to two transmembrane proteins, the low density lipoprotein receptor-related proteins (LRP) 5/6 and Kremen. Here, we show that Dkk1 residues Arg197, Ser198, and Lys232 are specifically involved in its binding to Kremen rather than to LRP6. These residues are localized at a surface that is at the opposite side of the LRP6-binding surface based on a three-dimensional structure of Dkk1 deduced from that of Dkk2. We were surprised to find that the Dkk1 mutants carrying a mutation at Arg197, Ser198, or Lys232, the key Kremen-binding residues, could antagonize Wnt signaling as well as the wild-type Dkk1. These mutations only affected their ability to antagonize Wnt signaling when both LRP6 and Kremen were coexpressed. These results suggest that Kremen may not be essential for Dkk1-mediated Wnt antagonism and that Kremen may only play a role when cells express a high level of LRP5/6.
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