Structural highlights
Function
[KAI2_ARATH] Involved in seed germination and seedling development. Essential for plant responses to karrikins, a class of butenolide compounds, structurally similar to strigolactones, released from burning vegetation that stimulate seed germination and enhance seedling photomorphogenesis. KAI2 is not required for strigolactone-mediated responses, but MAX2 is necessary for responses to karrikins and strigolactones.[1] [2] [3] [4]
Publication Abstract from PubMed
Genetic studies in Arabidopsis implicate an alpha/beta-hydrolase, KARRIKIN-INSENSITIVE 2 (KAI2) as a receptor for karrikins, germination-promoting butenolide small molecules found in the smoke of burned plants. However, direct biochemical evidence for the interaction between KAI2 and karrikin and for the mechanism of downstream signaling by a KAI2-karrikin complex remain elusive. We report crystallographic analyses and ligand-binding experiments for KAI2 recognition of karrikins. The karrikin-1 (KAR1) ligand sits in the opening to the active site abutting a helical domain insert but distal from the canonical catalytic triad (Ser95-His246-Asp217) of alpha/beta-hydrolases, consistent with the lack of detectable hydrolytic activity by purified KAI2. The closest approach of KAR1 to Ser95-His246-Asp217 is 3.8 A from His246. Six aromatic side chains, including His246, encapsulate KAR1 through geometrically defined aromatic-aromatic interactions. KAR1 binding induces a conformational change in KAI2 at the active site entrance. A crevice of hydrophobic residues linking the polar edge of KAR1 and the helical domain insert suggests that KAI2-KAR1 creates a contiguous interface for binding signaling partners in a ligand-dependent manner.
Smoke-derived karrikin perception by the alpha/beta-hydrolase KAI2 from Arabidopsis.,Guo Y, Zheng Z, La Clair JJ, Chory J, Noel JP Proc Natl Acad Sci U S A. 2013 Apr 23. PMID:23613584[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Sun XD, Ni M. HYPOSENSITIVE TO LIGHT, an alpha/beta fold protein, acts downstream of ELONGATED HYPOCOTYL 5 to regulate seedling de-etiolation. Mol Plant. 2011 Jan;4(1):116-26. doi: 10.1093/mp/ssq055. Epub 2010 Sep 23. PMID:20864454 doi:10.1093/mp/ssq055
- ↑ Waters MT, Nelson DC, Scaffidi A, Flematti GR, Sun YK, Dixon KW, Smith SM. Specialisation within the DWARF14 protein family confers distinct responses to karrikins and strigolactones in Arabidopsis. Development. 2012 Apr;139(7):1285-95. doi: 10.1242/dev.074567. Epub 2012 Feb 22. PMID:22357928 doi:10.1242/dev.074567
- ↑ Waters MT, Smith SM. KAI2- and MAX2-mediated responses to karrikins and strigolactones are largely independent of HY5 in Arabidopsis seedlings. Mol Plant. 2013 Jan;6(1):63-75. doi: 10.1093/mp/sss127. Epub 2012 Nov 9. PMID:23142794 doi:10.1093/mp/sss127
- ↑ Kagiyama M, Hirano Y, Mori T, Kim SY, Kyozuka J, Seto Y, Yamaguchi S, Hakoshima T. Structures of D14 and D14L in the strigolactone and karrikin signaling pathways. Genes Cells. 2013 Jan 10. doi: 10.1111/gtc.12025. PMID:23301669 doi:10.1111/gtc.12025
- ↑ Guo Y, Zheng Z, La Clair JJ, Chory J, Noel JP. Smoke-derived karrikin perception by the alpha/beta-hydrolase KAI2 from Arabidopsis. Proc Natl Acad Sci U S A. 2013 Apr 23. PMID:23613584 doi:10.1073/pnas.1306265110
