Highlights d The activities of LSD1 and HDAC1 are closely coupled in the CoREST complex d Both LSD1 and HDAC1 exist in two different kinetic states d CoREST has a bi-lobed, flexible structure with the two enzymes located at opposite ends d CoREST interacts with methylated nucleosomes via LSD1, but not HDAC1 or RCOR1

The von Willebrand factor (VWF) and coagulation factor VIII (FVIII) are intricately involved in hemostasis. A tight, noncovalent complex between VWF and FVIII prolongs the half-life of FVIII in plasma, and failure to form this complex leads to rapid clearance of FVIII and bleeding diatheses such as hemophilia A and von Willebrand disease (VWD) type 2N. High-resolution insight into the complex between VWF and FVIII has so far been strikingly lacking. This is particularly the case for the flexible a3 region of FVIII, which is imperative for high-affinity binding. Here, a structural and biophysical characterization of the interaction between VWF and FVIII is presented with focus on two of the domains that have been proven pivotal for mediating the interaction, namely the a3 region of FVIII and the TIL'E' domains of VWF. Binding between the FVIII a3 region and VWF TIL'E' was here observed using NMR spectroscopy, where chemical shift changes were localized to two b-sheet regions on the edge of TIL'E' upon FVIII a3 region binding. Isothermal titration calorimetry and NMR spectroscopy were used to characterize the interaction between FVIII and TIL'E' as well as mutants of TIL'E', which further highlights the importance of the b-sheet region of TIL'E' for high-affinity binding. Overall, the results presented provide new insight into the role the FVIII a3 region plays for complex formation between VWF and FVIII and the b-sheet region of TIL'E' is shown to be important for FVIII binding. Thus, the results pave the way for further high-resolution insights into this imperative complex.Editor: David Eliezer. SIGNIFICANCE The complex between von Willebrand factor (VWF) and factor VIII (FVIII) is imperative for hemostasis, and failure to form this complex leads to bleeding diatheses such as hemophilia A and von Willebrand disease (VWD). The FVIII a3 acidic region is shown to interact with VWF TIL'E', and the a3 binding region is localized to two b-sheet regions on the periphery of TIL'. Characterizations of the interaction between FVIII and mutants of VWF TIL'E' further highlight the importance of the b-sheet region for binding. The insight into VWF:FVIII complex formation facilitate the design of improved hemophilia A treatments, whereas the analysis of VWD mutations provides a link between genetic pathology and clinical phenotype to facilitate targeted management of patients with VWD.