From Proteopediaproteopedia link
Crystal Structure of TRF2 TRFH domain and APOLLO peptide complex
[DCR1B_HUMAN] Defects in DCLRE1B may be a cause of Hoyeraal-Hreidarsson syndrome (HHS) [MIM:300240]. HHS is a multisystem disorder affecting males and is characterized by aplastic anemia, immunodeficiency, microcephaly, cerebellar hypoplasia, and growth retardation. Note=An aberrant splice variant designated Apollo-Delta has been found in a patient with Hoyeraal-Hreidarsson syndrome. Apollo-Delta hampers the proper replication of telomeres, leading to major telomeric dysfunction and cellular senescence, but maintains its DNA interstrand cross-link repair function in the whole genome.
[TERF2_HUMAN] Binds the telomeric double-stranded 5'-TTAGGG-3' repeat and plays a central role in telomere maintenance and protection against end-to-end fusion of chromosomes. In addition to its telomeric DNA-binding role, required to recruit a number of factors and enzymes required for telomere protection, including the shelterin complex, TERF2IP/RAP1 and DCLRE1B/Apollo. Component of the shelterin complex (telosome) that is involved in the regulation of telomere length and protection. Shelterin associates with arrays of double-stranded 5'-TTAGGG-3' repeats added by telomerase and protects chromosome ends; without its protective activity, telomeres are no longer hidden from the DNA damage surveillance and chromosome ends are inappropriately processed by DNA repair pathways. Together with DCLRE1B/Apollo, plays a key role in telomeric loop (T loop) formation by generating 3' single-stranded overhang at the leading end telomeres: T loops have been proposed to protect chromosome ends from degradation and repair. Required both to recruit DCLRE1B/Apollo to telomeres and activate the exonuclease activity of DCLRE1B/Apollo. Preferentially binds to positive supercoiled DNA. Together with DCLRE1B/Apollo, required to control the amount of DNA topoisomerase (TOP1, TOP2A and TOP2B) needed for telomere replication during fork passage and prevent aberrant telomere topology. Recruits TERF2IP/RAP1 to telomeres, thereby participating in to repressing homology-directed repair (HDR), which can affect telomere length.   [DCR1B_HUMAN] 5'-3' exonuclease that plays a central role in telomere maintenance and protection during S-phase. Participates in the protection of telomeres against non-homologous end-joining (NHEJ)-mediated repair, thereby ensuring that telomeres do not fuse. Plays a key role in telomeric loop (T loop) formation by being recruited by TERF2 at the leading end telomeres and by processing leading-end telomeres immediately after their replication via its exonuclease activity: generates 3' single-stranded overhang at the leading end telomeres avoiding blunt leading-end telomeres that are vulnerable to end-joining reactions and expose the telomere end in a manner that activates the DNA repair pathways. Together with TERF2, required to protect telomeres from replicative damage during replication by controlling the amount of DNA topoisomerase (TOP1, TOP2A and TOP2B) needed for telomere replication during fork passage and prevent aberrant telomere topology. Also involved in response to DNA damage: plays a role in response to DNA interstrand cross-links (ICLs) by facilitating double-strand break formation. In case of spindle stress, involved in prophase checkpoint.        
Publication Abstract from PubMed
Mammalian telomeres are protected by a six-protein complex, shelterin. Shelterin contains two closely related proteins, TRF1 and TRF2, which recruit various proteins to telomeres. Here we dissect the interactions of TRF1 and TRF2 with their shared binding partner, TIN2, and other shelterin accessory factors. TRF1 recognizes TIN2 using a conserved molecular surface in its TRF homology (TRFH) domain. However, this same surface does not act as a TIN2 binding site in TRF2, and TIN2 binding to TRF2 is mediated by a region outside the TRFH domain. Instead, the TRFH docking site of TRF2 binds a shelterin accessory factor Apollo, which does not interact with the TRFH domain of TRF1. Conversely, the TRFH domain of TRF1, but not of TRF2, interacts with another shelterin associated factor PinX1.
A Shared Docking Motif in TRF1 and TRF2 Used for Differential Recruitment of Telomeric Proteins.,Chen Y, Yang Y, van Overbeek M, Donigian JR, Baciu P, de Lange T, Lei M Science. 2008 Jan 17;. PMID:18202258
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.