Solution structure of the DNA-binding domain of human telomeric protein, hTRF1

Mammalian telomeres consist of long tandem arrays of the double-stranded TTAGGG sequence motif packaged by a telomere repeat binding factor, TRF1. The DNA-binding domain of TRF1 shows sequence homology to each of three tandem repeats of the DNA-binding domain of the transcriptional activator c-Myb. The isolated c-Myb-like domain of human TRF1 (hTRF1) binds specifically to telomeric DNA as a monomer, in a similar manner to that of homeodomains. So far, the only three-dimensional structure of a telomeric protein to be determined is that of a yeast telomeric protein, Rap 1p. The DNA-binding domain of Rap 1p contains two subdomains that are structurally closely related to c-Myb repeats. We set out to determine the solution structure of the DNA-binding domain of hTRF1 in order to establish its mode of DNA binding.

The solution structure of the DNA-binding domain of hTRF1 has been determined and shown to comprise three helices. The architecture of the three helices is very similar to that of each Rap 1p subdomain and also to that of each c-Myb repeat. The second and third helix form a helix-turn-helix (HTH) variant. The length of the third helix of hTRF1 is similar to that of the second subdomain of Rap 1p.

The hTRF1 DNA-binding domain is likely to bind to DNA in a similar manner to that of the second subdomain of Rap 1p. On the basis of the Rap 1p-DNA complex, a model of the hTRF1 DNA-binding domain in complex with human telomeric DNA was constructed. In addition to DNA recognition by the HTH variant, a flexible N-terminal arm of hTRF1 is likely to interact with DNA.