Rich Repeat

An example of a leucine-rich repeat protein, a porcine ribonuclease inhibitor
Identifiers
Symbol	LRR_1
Pfam	PF00560
Pfam clan	CL0022
InterPro	IPR001611
SCOP	2bnh
SUPERFAMILY	2bnh
OPM protein	1xwd
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Leucine rich repeat variant
a leucine-rich repeat variant with a novel repetitive protein structural motif
Identifiers
Symbol	LRV
Pfam	PF01816
Pfam clan	CL0020
InterPro	IPR004830
SCOP	1lrv
SUPERFAMILY	1lrv
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

LRR adjacent
internalin h: crystal structure of fused n-terminal domains.
Identifiers
Symbol	LRR_adjacent
Pfam	PF08191
InterPro	IPR012569
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Leucine rich repeat N-terminal domain
dimeric bovine tissue-extracted decorin, crystal form 2
Identifiers
Symbol	LRRNT
Pfam	PF01462
InterPro	IPR000372
SMART	LRRNT
SCOP	1m10
SUPERFAMILY	1m10
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Leucine rich repeat N-terminal domain
the crystal structure of pgip (polygalacturonase inhibiting protein), a leucine rich repeat protein involved in plant defense
Identifiers
Symbol	LRRNT_2
Pfam	PF08263
InterPro	IPR013210
SMART	LRRNT
SCOP	1m10
SUPERFAMILY	1m10
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Leucine rich repeat C-terminal domain
third lrr domain of drosophila slit
Identifiers
Symbol	LRRCT
Pfam	PF01463
InterPro	IPR000483
SMART	LRRCT
SCOP	1m10
SUPERFAMILY	1m10
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

LRV protein FeS4 cluster
a leucine-rich repeat variant with a novel repetitive protein structural motif
Identifiers
Symbol	LRV_FeS
Pfam	PF05484
Pfam clan	CL0020
InterPro	IPR008665
SCOP	1lrv
SUPERFAMILY	1lrv
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

A leucine-rich repeat (LRR) is a protein structural motif that forms an α/β horseshoe fold.^[1][2] It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine. These 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. The region between the helices and sheets is the protein's hydrophobic core and is tightly sterically packed with leucine residues.

Leucine-rich repeats are frequently involved in the formation of protein–protein interactions.^[3][4]

Examples

Leucine-rich repeat motifs have been identified in a large number of functionally unrelated proteins.^[5] The best-known example is the ribonuclease inhibitor, but other proteins such as the tropomyosin regulator tropomodulin and the toll-like receptor also share the motif. In fact, the toll-like receptor possesses 10 successive LRR motifs which serve to bind pathogen- and danger-associated molecular patterns.

Although the canonical LRR protein contains approximately one helix for every beta strand, variants that form beta-alpha superhelix folds sometimes have long loops rather than helices linking successive beta strands.

One leucine-rich repeat variant domain (LRV) has a novel repetitive structural motif consisting of alternating alpha- and 3(10)-helices arranged in a right-handed superhelix, with the absence of the beta-sheets present in other leucine-rich repeats.^[6]

Associated domains

Leucine-rich repeats are often flanked by N-terminal and C-terminal cysteine-rich domains.

They also co-occur with LRR adjacent domains. These are small, all beta strand domains, which have been structurally described for the protein Internalin (InlA) and related proteins InlB, InlE, InlH from the pathogenic bacterium Listeria monocytogenes. Their function appears to be mainly structural: They are fused to the C-terminal end of leucine-rich repeats, significantly stabilising the LRR, and forming a common rigid entity with the LRR. They are themselves not involved in protein-protein-interactions but help to present the adjacent LRR-domain for this purpose. These domains belong to the family of Ig-like domains in that they consist of two sandwiched beta sheets that follow the classical connectivity of Ig-domains. The beta strands in one of the sheets is, however, much smaller than in most standard Ig-like domains, making it somewhat of an outlier.^[7][8][9]

An iron sulphur cluster is found at the N-terminus of some proteins containing the leucine-rich repeat variant domain (LRV). These proteins have a two-domain structure, composed of a small N-terminal domain containing a cluster of four Cysteine residues that houses the 4Fe:4S cluster, and a larger C-terminal domain containing the LRV repeats.^[6] Biochemical studies revealed that the 4Fe:4S cluster is sensitive to oxygen, but does not appear to have reversible redox activity.

See also

• Leucine zipper

References

Further reading

External links

• Eukaryotic Linear Motif resource motif class LIG_SCF_Skp2-Cks1_1
• SCOP LRR fold
• CATH Alpha-beta horseshoe architecture
• LRRML: a conformational database of leucine-rich repeats

This article incorporates text from the public domain Pfam and InterPro IPR012569

This article incorporates text from the public domain Pfam and InterPro IPR013210

This article incorporates text from the public domain Pfam and InterPro IPR000372

This article incorporates text from the public domain Pfam and InterPro IPR000483

This article incorporates text from the public domain Pfam and InterPro IPR004830

This article incorporates text from the public domain Pfam and InterPro IPR004830