Analysis of repeated motifs in the talin rod.

The amino acid sequence of the rod portion of talin contains strong periodic patterns with a long period of 32 to 34 residues superimposed on short periods of 7 and 7/2 residues. The rod includes 50 to 60 copies of an irregular repeated motif approximately 34 residues long. The motif itself consists of three sections: a short "leader" segment of about six residues, which has a high proportion of the prolines and acidic residues; a relatively well-conserved hydrophobic "core" pattern of approximately 21 residues; and a highly variable "linker" region of seven residues which joins onto the next leader. The core section sequence has many of the characteristics of an amphipathic helix. The extensive hydrophobic side of this postulated helix has a characteristic surface pattern of large and small hydrophobic residues (mainly Leu and Ala), with a strong periodicity of seven residues. It also has a narrow hydrophilic edge with a highly variable sequence. The core sequence is unlike either a normal helical coiled coil or a leucine zipper, because it contains several helical ridges and grooves. The helical cores probably form a tightly packed hydrophobic central strand for the fibrous tail. The leader and linker sections are highly variable in length, so that the spacing between the starting points of adjacent cores varies between 20 and 40 residues. The most common spacing is 34, and many spacings are close to this length.