Crystal structures of two tandem malectin‐like receptor kinases involved in plant reproduction

• Published in: Acta crystallographica. Section D, Biological crystallography. Biological crystallography., 2018-07, Vol.74 (7), p.671-680
• Main Authors: Moussu, Steven, Augustin, Sebastian, Roman, Andra-Octavia, Broyart, Caroline, Santiago, Julia
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis Proteins - chemistry; Binding Sites; Calcium; Calcium - pharmacology; Calcium ions; Carbohydrates; Catharanthus - enzymology; Catharanthus roseus; Cell interactions; cell signalling; cell‐wall signalling; Crystal structure; Crystallography, X-Ray; Fertilization; Glycosylation; Kinases; malectin‐like receptor kinases; membrane receptors; membrane signalling; Oligosaccharides; Organic chemistry; Organs; Plant Proteins - chemistry; plant reproductive signalling; Plant reproductive structures; Protein Conformation; Protein Domains; Protein Interaction Domains and Motifs; Protein Kinases - chemistry; Protein Kinases - physiology; Proteins; receptor kinases; Receptor mechanisms; Receptors; Reproduction; Research Papers
• ISSN: 2059-7983; 0907-4449; 2059-7983; 1399-0047
• DOI: 10.1107/S205979831800774X

Complex cell‐to‐cell communication between the male pollen tube and the female reproductive organs is required for plant fertilization. A family of Catharanthus roseus receptor kinase 1‐like (CrRLK1L) membrane receptors has been genetically implicated in this process. Here, crystal structures of the CrRLK1Ls ANXUR1 and ANXUR2 are reported at 1.48 and 1.1 Å resolution, respectively. The structures reveal a novel arrangement of two malectin‐like domains connected by a short β‐hairpin linker and stabilized by calcium ions. The canonical carbohydrate‐interaction surfaces of related animal and bacterial carbohydrate‐binding modules are not conserved in plant CrRLK1Ls. In line with this, the binding of chemically diverse oligosaccharides to ANXUR1 and HERCULES1 could not be detected. Instead, CrRLK1Ls have evolved a protein–protein interface between their malectin domains which forms a deep cleft lined by highly conserved aromatic and polar residues. Analysis of the glycosylation patterns of different CrRLK1Ls and their oligomeric states suggests that this cleft could resemble a binding site for a ligand required for receptor activation of CrRLK1Ls. The biochemical and crystallographic characterization of different Catharanthus roseus receptor kinase 1‐like membrane receptors is reported as a first step to understand cell‐wall sensing and signalling mechanisms in plants.