 These tandem repeats commonly fold together to form a solenoid protein domain, termed leucine-rich repeat domain.Typically, each repeat unit has beta strand-turn-alpha helix structure, and the assembled domain, composed of many such repeats, has a horseshoe shape with an interior parallel beta sheet and an exterior array of helices.One face of the beta sheet and one side of the helix array are exposed to solvent and are therefore dominated by hydrophilic residues.