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Structural modules for receptor dimerization in the S-locus receptor kinase extracellular domain

Authors :
Naithani, Sushma
Chookajorn, Thanat
Ripoll, Daniel R.
Nasrallah, June B.
Source :
Proceedings of the National Academy of Sciences of the United States. July 17, 2007, Vol. 104 Issue 29, p12211, 6 p.
Publication Year :
2007

Abstract

The highly polymorphic S-locus receptor kinase (SRK) is the stigma determinant of specificity in the self-incompatibility response of the Brassicaceae. SRK spans the plasma membrane of stigma epidermal cells, and it is activated in an allele-specific manner on binding of its extracellular region (eSRK) to its cognate pollen coat-localized S-locus cysteine-rich (SCR) ligand. SRK, like several other receptor kinases, forms dimers in the absence of ligand. To identify domains in SRK that mediate ligand-independent dimerization, we assayed eSRK for self-interaction in yeast. We show that SRK dimerization is mediated by two regions in eSRK, primarily by a C-terminal region inferred by homology modeling/fold recognition techniques to assume a PAN_APPLE-like structure, and secondarily by a region containing a signature sequence of the S-domain gene family, which might assume an EGF-like structure. We also show that eSRK exhibits a marked preference for homodimerization over heterodimerization with other eSRK variants and that this preference is mediated by a small, highly variable region within the PAN_APPLE domain. Thus, the extensive polymorphism exhibited by the eSRK not only determines differential affinity toward the SCR ligand, as has been assumed thus far, but also underlies a previously unrecognized allelic specificity in SRK dimerization. We propose that preference for SRK homodimerization explains the codominance exhibited by a majority of SRKs in the typically heterozygous stigmas of self-incompatible plants, whereas an increased propensity for heterodimerization combined with reduced affinity of heterodimers for cognate SCRs might underlie the dominant-recessive or mutual weakening relationships exhibited by some SRK allelic pairs. self-incompatibility | ligand-independent receptor dimerization | yeast two-hybrid

Details

Language :
English
ISSN :
00278424
Volume :
104
Issue :
29
Database :
Gale General OneFile
Journal :
Proceedings of the National Academy of Sciences of the United States
Publication Type :
Academic Journal
Accession number :
edsgcl.167305973