The human centromere protein B (CENP-B), a centromeric heterochromatin component, forms a homodimer that specifically binds to a distinct DNA sequence (the CENP-B box), which appears within every other α-satellite repeat. Previously, we determined the structure of the human CENP-B DNA-binding domain, CENP-B-(1-129), complexed with the CENP-B box DNA. In the present study, we determined the crystal structure of its dimerization domain (CENP-B-(540-599)), another functional domain of CENP-B, at 1.65-Å resolution. CENP-B-(540-599) contains two α-helices, which are folded into an antiparallel configuration. The CENP-B-(540-599) dimer formed a symmetrical, antiparallel, four-helix bundle structure with a large hydrophobic patch in which 23 residues of one monomer form van der Waals contacts with the other monomer. In the CENP-B-(540-599) dimer, the N-terminal ends of CENP-B-(540-599) are oriented on opposite sides of the dimer. This CENP-B dimer configuration may be suitable for capturing two distant CENP-B boxes during centromeric heterochromatin formation.
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