May function as protective capping of the single-stranded telomeric overhang. May also participate in telomere length regulation during DNA replication. Binds specifically to the T4G4-containing extension on the 3'strand and protects this region of the telomere from nuclease digestion and chemical modification. Heterodimer of an alpha and a beta subunit. The sequence of the A (or alanine) version is shown. The S (or serine) version differs in only two positions, and the K version in only one. There may be other versions in addition to the S, A, and K versions. Belongs to the telombin family.