An Integrated Structural Model of the DNA Damage Responsive H3K4me3 Binding WDR76:SPIN1 Complex with the Nucleosome

Serial Capture Affinity Purification (SCAP) is a powerful method to isolate a specific protein complex. When combined with cross linking mass spectrometry (XL-MS) and computational approaches one can build an integrated structural model of the isolated complex. Here, we applied SCAP to dissect a subpopulation of WDR76 in complex with SPIN1, a histone marker reader that specifically recognizes trimethylated histone H3 lysine4 (H3K4me3). In contrast to a previous SCAP analysis of the SPIN1:SPINDOC complex, histones and the H3K4me3 mark were copurified with the WDR76:SPIN1 complex. Next, interaction network analysis of copurifying proteins and microscopy analysis revealed a potential role of the WDR76:SPIN1 complex in the DNA damage response. Since we detected an extensive number of cross-linked sites were found between WDR76, SPIN1, and histones, we first built an integrated structural model of the complex which revealed that SPIN1 recognized the H3K4me3 epigenetic mark while interacting with WDR76. Finally, we then used the powerful Integrative Modeling Platform to build a structural model of WDR76 and SPIN1 bound to the nucleosome.