Focal adhesion kinase (FAK) is a tyrosine kinase found in focal adhesions, intracellular signaling complexes that are formed following engagement of the extracellular matrix by integrins. The C-terminal 'focal adhesion targeting' (FAT) region is necessary and sufficient for localising FAK to focal adhesions. The crystal structure of FAT shows it forms a four-helix bundle that resembles those found in two other proteins involved in cell adhesion, alpha-catenin and vinculin [1]. The binding of FAT to the focal adhesion protein, paxillin, requires the integrity of the helical bundle, whereas binding to another focal adhesion protein, talin, does not.

1: The focal adhesion targeting (FAT) region of focal adhesion kinase is a four-helix bundle that binds paxillin. Hayashi I, Vuori K, Liddington RC; Nat Struct Biol 2002;9:101-106. PMID:11799401

2: Focal adhesion targeting: the critical determinant of FAK regulation and substrate phosphorylation. Shen Y, Schaller MD; Mol Biol Cell 1999;10:2507-2518. PMID:10436008