Structural principles of leucine‐rich repeat (LRR) proteins

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Abstract
LRR‐containing proteins are present in over 2000 proteins from viruses to eukaryotes. Most LRRs are 20–30 amino acids long, and the repeat number ranges from 2 to 42. The known structures of 14 LRR proteins, each containing 4–17 repeats, have revealed that the LRR domains fold into a horseshoe (or arc) shape with a parallel β‐sheet on the concave face and with various secondary structures, including α‐helix, 310‐helix, and pII helix on the convex face. We developed simple methods to charactere quantitatively the arc shape of LRR and then applied them to all known LRR proteins. A quantity of 2Rsin(φ/2), in which R and φ are the radii of the LRR arc and the rotation angle about the central axis per repeating unit, respectively, is highly conserved in all the LRR proteins regardless of a large variety of repeat number and the radius of the LRR arc. The radii of the LRR arc with β‐α structural units are smaller than those with β‐310 or β‐pII units. The concave face of the LRR β‐sheet forms a surface analogous to a part of a Möbius strip. Proteins 2004;54:000–000.