A common binding motif in the ET domain of BRD3 forms polymorphic structural interfaces with host and viral proteins

The extra-terminal (ET) domain of BRD3 is conserved among BET proteins (BRD2, BRD3, BRD4), interacting with multiple host and viral protein-protein networks. Solution NMR structures of complexes formed between BRD3-ET domain with either the 79-residue murine leukemia virus integrase (IN) C-terminal domain (IN329-408), or its 22-residue IN tail peptide (TP) (IN386-407) alone, reveal similar intermolecular three-stranded {beta}-sheet formation. 15N relaxation studies reveal a 10-residue linker region (IN379-388) tethering the SH3 domain (IN329-378) to the ET-binding motif (IN389-405)-ET complex. This linker has restricted flexibility, impacting its potential range of orientations in the IN - nucleosome complex. The complex of the ET-binding peptide of host NSD3 protein (NSD3148-184) and BRD3-ET domain includes a similar three-stranded {beta}-sheet interaction, but the orientation of the {beta}-hairpin is flipped compared to the two IN : ET complexes. These studies expand our understanding of molecular recognition polymorphism in complexes of ET-binding motifs with viral and host proteins. HighlightsO_LIThe BRD3 ET domain binds to key peptide motifs of diverse host and viral proteins. C_LIO_LIThese complexes reveal conformational plasticity in molecular recognition. C_LIO_LINMR studies demonstrate restricted interdomain motion in the IN CTD / ET complex. C_LIO_LIA cost-effective approach is described for producing isotopically-labeled peptides. C_LI Etoc BlurbWe address structurally how the MLV Integrase (IN) usurps the host function of the BET protein through comparative studies of the IN : Brd3 ET complex with that of the host NSD3. MLV integration and thus its pathogenesis is driven through protein interactions of the IN : BET family.