RNA provisions detached from photocells 2448 after transfection
However, as these Trp or Cys residues are conserved in many other plant eLRR proteins as well, they likely contribute to the conformation and stability of the protein rather than to ligand specificity. In addition, another site-directed mutagenesis strategy focused on putative N-linked glycosylation sites, which frequently occur in the eLRR domain of cell surface receptors. Through Asn to Asp substitution, van der Hoorn et al demonstrated that four glycosylation sites contribute to Cf-9 functionality. These four sites are located in putative a-helixes that are exposed at the convex surface of the Cf-9 eLRR domain and are also conserved in many plant eLRR proteins. Glycosylation may contribute to protein conformation, facilitate interactions with the cell wall, or protect proteins from degradation. However, it seems unlikely that these putative glycosylation sites contribute to ligand specificity of Cf-9. Most of the Ve1 glycosylation sites are located at convex face of the eLRR domain, and thus they were not specifically targeted in our study. To the best of our knowledge, no examples of ligand perception at convex side of the eLRR domain have been reported. Moreover, N-linked glycosylation was determined to make only subtle quantitative contributions to FLS2 functionality. In contrast, alanine scanning mutagenesis on the concave b-sheet surface across the Arabidopsis FLS2 eLRR domain identified eLRR9-eLRR15 as contributors to flagellin perception. To identify eLRRs that are required for Ve1 ligand recognition, we focused our attention on the concave b-sheet surface and evaded conserved hydrophobic leucine residues in bsheets that are likely involved in framework of protein. A doublealanine scanning was performed in which two of the five variable, solvent exposed residues in a single eLRR repeat were mutated. Mutagenesis of two non-adjacent amino acids increases the chance of substituting functionally important residues. In this study, we showed that mutant alleles that reveal compromised Ve1 function are restricted to three consecutive eLRR regions, eLRR1-eLRR8, eLRR20-eLRR23 and eLRR32- eLRR37. This is consistent with previously studies, in which Elrr function was found to be determined by solvent-exposed residues in clustered LRRs of the concave b-sheet surface. For example, domain swaps of tomato Cfs revealed that eLRR13-eLRR16 of Cf-4 contribute to ligand specificity, while ligand specificity of Cf-9 is determined by eLRR10-eLRR16. In addition, photoaffinity labelling showed that BAM1 directly interacts with the small peptide ligand CLE9 at the eLRR6-eLRR8 region. Finally, the crystal structure of PGIP showed that the concave surface of eLRR4-eLRR8 is involved in polygalacturonase binding. Similarly, crystallographic studies revealed that brassinosteroid binds to a hydrophobic groove of BRI1 in between the island domain and the concave b-sheet surface of eLRR20-eLRR25. Significantly, crystal structure analysis showed that flg22 binds to the concave surface of FLS2 eLRR3 to eLRR16. This similarly holds true for the eLRR domain of mammalian TLRs, for example, a crystal structure of the TLR4-MD-2-LPS complex demonstrated that the TLR4 interaction with cofactor MD-2 is restricted to the concave b-sheet surface of two eLRR clusters, eLRR2-eLRR5 and eLRR8-eLRR10. Because ligand specificity is often determined by the C1 domain, we previously suggested that this may similarly be true for Ve1. Therefore, the two regions eLRR1-eLRR8 and eLRR20-eLRR23 are proposed to contribute to ligand binding. However, most of the mutant alleles in the C3 domain also abolished Ve1 function. This finding is consistent with previous domain swap experiments between Ve1 and Ve2, which demonstrated that the C3 domain of Ve2 is not able to activate successful immune signaling. Similar to Ve1, alanine scanning of the C3 domain of Cf-9, which is rather conserved when compared with the C3 domain of Ve1, compromised its functionality. This is also consistent with previous mutagenesis studies on Cf-9, where Wulff et al showed that the Ser675Leu mutation in the solvent-exposed resides of the concave side of the Cf-9 eLRR24 in the C3 domain abolished functionality. Similarly, van der Hoorn et al proved that Cf-9 function is compromised upon Asp substitution of Asn697, which is located on the concave side of eLRR25. In addition, a Glu662Val mutation in Cf-4 similarly showed the importance of concave side of the eLRR C3 domain. It has previously been demonstrated that the C3 domains of the Cf-4 and Cf-9 receptors, that perceive sequence-unrelated effector proteins Avr4 and Avr9, respectively, is identical, supporting a role in immune signaling rather than in ligand perception. The classical cadherins are single pass trans-membrane proteins having divergent extracellular domains with five cadherin-type repeats and a conserved cytoplasmic domain. The extracellular regions mediate specific cell-cell interactions. Cadherins expressed on the surface of a cell interact with similar molecules expressed on other cells. These homophilic interactions mediate cell sorting, create cellular sheets like germ layers, epithelia etc., as well as maintain their integrity. Mutations in certain cadherins, Ecadherin and C-cadherin, have been shown to interrupt gastrulation in frog and fish respectively. The intracellular regions of cadherins interact with a number of cytoplasmic proteins, the best characterized of which are catenins like b-catenin, plakoglobin and p120. Through interaction with cytosolic proteins and cytoskeletal elements cadherins coordinate a large range of cellular functions including cytoskeletal reorganization and signal transduction.