Structural Basis of DNA Bridging by Barrier-to-Autointegration Factor

• Published in: Biochemistry (Easton) 2000-08, Vol.39 (31), p.9130-9138
• Main Authors: Umland, Timothy C, Wei, Shui-Qing, Craigie, Robert, Davies, David R
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Barrier-to-autointegration factor; Binding Sites - genetics; Computer Simulation; Crystallography, X-Ray; Dimerization; DNA; DNA - chemistry; DNA Mutational Analysis; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; Helix-Turn-Helix Motifs - genetics; Humans; lamina-associated polypeptide 2; Models, Molecular; Molecular Sequence Data; Moloney murine leukemia virus - chemistry; Moloney murine leukemia virus - genetics; Mutagenesis, Site-Directed; Nuclear Magnetic Resonance, Biomolecular; Nuclear Proteins; Protein Folding; Retrovirus; Selenomethionine - chemistry; Solutions; Virus Integration
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi000572w

Barrier-to-autointegration factor (BAF) is a host cell protein that plays a crucial role in retroviral integration. Preintegration complexes (PICs) stripped of BAF lose their normal integration activity, which can be restored by incubation with purified BAF. BAF bridges double-stranded DNA both intra- and intermolecularly in a non-sequence-specific manner, leading to the formation of a nucleoprotein network. BAF also binds to the nuclear protein lamina-associated polypeptide 2 (LAP2), and is localized with chromatin during interphase and mitosis. The crystal structure of homodimeric human BAF has been determined to 1.9 Å resolution. The fold of the BAF monomer resembles that of the second domain of RuvA. This comparison revealed the presence of the helix−hairpin−helix (HhH) nonspecific DNA binding motif within BAF. A novel feature of BAF's HhH motif is the occupation of the metal binding site by the ε-amino group of Lys 6, providing an alternative means of sequestering positive charge. Mutational analysis corroborates the HhH motif's prominent role in DNA binding and argues against a previously proposed helix−turn−helix (HTH) binding site located in another region of the monomer. A model of BAF bridging DNA via the HhH motif is proposed.