Jizong Wang

Allosteric receptor activation by the plant peptide hormone phytosulfokine

Phytosulfokine (PSK) is a disulfated pentapeptide that has a ubiquitous role in plant growth and development. PSK is perceived by its receptor PSKR, a leucine-rich repeat receptor kinase (LRR-RK). The mechanisms underlying the recognition of PSK, the activation of PSKR and the identity of the components downstream of the initial binding remain elusive. Here we report the crystal structures of the extracellular LRR domain of PSKR in free, PSK- and co-receptor-bound forms. The structures reveal that PSK interacts mainly with a β-strand from the island domain of PSKR, forming an anti-β-sheet. The two sulfate moieties of PSK interact directly with PSKR, sensitizing PSKR recognition of PSK. Supported by biochemical, structural and genetic evidence, PSK binding enhances PSKR heterodimerization with the somatic embryogenesis receptor-like kinases (SERKs). However, PSK is not directly involved in PSKR–SERK interaction but stabilizes PSKR island domain for recruitment of a SERK. Our data reveal the structural basis for PSKR recognition of PSK and allosteric activation of PSKR by PSK, opening up new avenues for the design of PSKR-specific small molecules.

Deposition of PTFE thin films by ion beam sputtering and a study of the ion bombardment effect

Abstract Ion beam sputtering technique was employed to prepare thin films of Polytetrafluroethylene (PTFE). Simultaneous ion beam bombardment during film growth was also conducted in order to study the bombardment effects. Infrared absorption (IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis was used to evaluate the materials integrity. It was found that PTFE thin films could be grown at room temperature by direct sputtering of a PTFE target. The films composition and structure were shown to be dependent on the sputtering energy. Films deposited by single sputtering at higher energy (∼1500 eV) were structurally quite similar to the original PTFE material. Simultaneous ion beam bombarding during film growth caused defluorination and structural changes. Mechanism for sputtering deposition of such a polymeric material is also discussed.

Signature motif-guided identification of receptors for peptide hormones essential for root meristem growth.

Peptide-mediated cell-to-cell signaling has crucial roles in coordination and definition of cellular functions in plants. Peptide-receptor matching is important for understanding the mechanisms underlying peptide-mediated signaling. Here we report the structure-guided identification of root meristem growth factor (RGF) receptors important for plant development. An assay based on a signature ligand recognition motif (Arg-x-Arg) conserved in a subfamily of leucine-rich repeat receptor kinases (LRR-RKs) identified the functionally uncharacterized LRR-RK At4g26540 as a receptor of RGF1 (RGFR1). We further solved the crystal structure of RGF1 in complex with the LRR domain of RGFR1 at a resolution of 2.6 Å, which reveals that the Arg-x-Gly-Gly (RxGG) motif is responsible for specific recognition of the sulfate group of RGF1 by RGFR1. Based on the RxGG motif, we identified additional four RGFRs. Participation of the five RGFRs in RGF-induced signaling is supported by biochemical and genetic data. We also offer evidence showing that SERKs function as co-receptors for RGFs. Taken together, our study identifies RGF receptors and co-receptors that can link RGF signals with their downstream components and provides a proof of principle for structure-based matching of LRR-RKs with their peptide ligands.

Structural insights into the negative regulation of BRI1 signaling by BRI1-interacting protein BKI1

Brassinosteroids (BRs) are essential steroid hormones that have crucial roles in plant growth and development. BRs are perceived by the cell-surface receptor-like kinase brassinosteroid insensitive 1 (BRI1). In the absence of BRs, the cytosolic kinase domain (KD) of BRI1 is inhibited by its auto-inhibitory carboxyl terminus, as well as by interacting with an inhibitor protein, BRI1 kinase inhibitor 1 (BKI1). How BR binding to the extracellular domain of BRI1 leads to activation of the KD and dissociation of BKI1 into the cytosol remains unclear. Here we report the crystal structure of BRI1 KD in complex with the interacting peptide derived from BKI1. We also provide biochemical evidence that BRI1-associated kinase 1 (BAK1) plays an essential role in initiating BR signaling. Steroid-dependent heterodimerization of BRI1 and BAK1 ectodomains brings their cytoplasmic KDs in the right orientation for competing with BKI1 and transphosphorylation.

Structural insights into ligand recognition and activation of plant receptor kinases

The large family of membrane-localized receptor kinases (RKs) has important roles in many aspects of plant physiology. RKs function to perceive external signals, leading to RK activation and downstream signaling. Progress has been recently made in structural elucidation of the mechanisms underlying ligand recognition and activation of RKs. These structural studies mainly on leucine-rich repeat RKs (LRR-RKs) support the idea that ligand-induced dimerization is an essential step for RK activation, though the modes for dimerization vary. Here we review the structural knowledge with an emphasis on the ligand recognition and activation mechanisms that are likely conserved in a subfamily of LRR-RKs.

Simulation of nacre with TiN/Pt multilayers and a study of their mechanical properties

Abstract TiN/Pt multilayers with individual layer thickness between 1 and 8 nm have been prepared by ion beam sputtering deposition to simulate the nacreous structure in natural nacre. Both the hardness and toughness were systematically investigated together with a study of structures of the multilayer. It was found that [111] texture developed during the alternative deposition of TiN and Pt. The multilayer toughness was higher than that of pure TiN. The hardness was greater than the volume weighted mean of the hardness of two components (i.e. TiN and Pt). Both the multilayer hardness and toughness showed a strong dependence on the individual layer thickness arrangement. When the individual thickness was properly adjusted, the multilayer can even be harder than its hard component (TiN) while the toughness was also greatly improved. Annealing experiment indicated that such an enhancement was an intrinsic property of the multilayers. Some suggestions for microdesigning of materials are thus proposed.

Simulation of nacre with TiC/Teflon multilayers and a study of their properties

Abstract Ion beam sputter deposition was employed to prepare nanoscale multilayers of TiC and a polymeric material, Teflon. The multilayers were synthesized to simulate nacre not only on laminated structures but also on individual layer thicknesses. The laminated architecture was studied as well as the structures of individual layers. Multilayer toughness and hardness were systematically investigated. It was found that the toughness of TiC/Teflon multilayers was significantly improved in comparison with monolithic TiC. But the multilayer hardness experienced a serious decrease. The individual layer thickness arrangement had an influence on both the multilayer hardness and the toughness.

Study on nanostructural morphology of Si3N4/TiN multilayer synthesized by ion beam assisted deposition

Abstract The structure and morphology of Si 3 N 4 /TiN multilayer synthesized by ion beam assisted deposition (IBAD) were studied by X-ray diffraction (XRD), Auger electron spectrum (AES) and Field-emmision scanning electron microscopy (FESEM). It was found that a well-defined multilayer structure was formed. The multilayer was composed of polycrystalline TiN and amorphous Si 3 N 4 . The compositions were determined as N:Ti=1 and N:Si=0.9, respectively. Ion beam etching technique was employed to prepare special specimen for FESEM morphology observation. Cross-sectional FESEM was also conducted. Results showed that the Si 3 N 4 layers consisted of granular particles of about 100 nm in size and the particles in TiN layers were much smaller.

Structural Insight into Recognition of Plant Peptide Hormones by Plant Receptor Kinases

Plant growth and development are precisely regulated by the plant hormone systems. Peptide hormone signaling is initiated upon perception by their receptors, which belong to the membrane-anchored receptor kinases (RKs). Activation of RKs by peptide hormones induces downstream events in cytoplasm. Recent structural studies provide significant insight into the molecular mechanisms underlying peptide hormone recognition by their receptors. Structural comparison suggests a conserved mechanism of receptor binding among a subset of peptide hormones. Here we provide a summary of these structural data and suggest some directions for future structural studies.