1 Crystal structure of archaeal chromatin protein Alba 2-dsDNA complex from Aeropyrum pernix K 1

All thermophilic and hyperthermophilic archaea encode homologs of dimeric Alba (Sac10b) proteins that bind cooperatively at high density to DNA. Here, we report the 2.0 Å resolution crystal structure of an Alba2 (Ape10b2)-dsDNA complex from Aeropyrum pernix K1. A rectangular tube-like structure encompassing duplex DNA reveales the positively charged residues in the monomer-monomer interface of each dimer packing on either side of the bound dsDNA in successive minor grooves. The extended hairpin loop connecting the strands β3-β4 undergoes significant conformational changes upon DNA-binding to accommodate the other Alba2-dimer during oligomerization. Mutational analysis of key interacting residues confirmed the specificity of Alba2-dsDNA interactions.