Crystal structure of human dynein light chain Dnlc2A: structural insights into the interaction with IC74.

The human light chain of the motor protein dynein, Dnlc2A, is also a novel TGF-beta-signaling component, which is altered with high frequency in epithelial ovarian cancer. It is an important mediator of dynein and the development of cancer, owing to its ability to bind to the dynein intermediate light chain (DIC) IC74 and to regulate TGF-beta-dependent transcriptional events. Here we report the 2.1-A crystal structure of Dnlc2A using single anomalous diffraction. The proteins form a homodimer in solution and interact mainly through the helix alpha(2), strand beta(3), and the loop following this strand in each protein to generate a 10-stranded beta-sheet core. The surface of the beta-sheet core is mainly positively charged and predicted (by software PPI-Pred) to be the site that interacts with other partners. At the same time, the residues 79-82, 88, and 90 of each molecule formed two holes in the core. Residue 89 of each molecule, which is crucial for the DIC binding function of Dnlc2A, is within the holes. On the basis of these observations, we propose that the homodimer is the structural and functional unit maintained by hydrogen bonding interactions and hydrophobic packing, and that the patch of the surface of the beta-sheet core is the main area of interaction with other partners. Furthermore, the two holes would be the key sites to interact with IC74.