SPATIALLY-LOCALIZED SCAFFOLD PROTEINS MAY FACILITATE TO TRANSMIT LONG-RANGE SIGNALS

Scaffold proteins play an important role in the promotion of signal transmission and specificity during cell signaling. In cells, signaling proteins that make up a pathway are often physically orgnaized into complexes by scaffold proteins [1]. Previous work [2] has shown that spatial localization of scaffold can enhance signaling locally while simultaneously suppressing signaling at a distance, and the membrane confinement of scaffold proteins may result in a precipitous spatial gradient of the active product protein, high close to the membrane and low within the cell. However, cell-fate decisions critically depend on the temporal pattern of product protein close to the nucleus. In this paper, when phosphorylation signals cannot be transfered by diffusion only, two mechanisms have been proposed for long-range signaling within cells： multiple locations of scaffold proteins and dynamical movement of scaffold proteins. Thus, here we have unveiled how the spatial propagation of the phosphorylated product protein within a cell depends on the spatially and temporal localized scaffold proteins. A class of novel and fast numerical methods for solving stiff reaction diffusion equations with complex domains is briefly introduced.

Homer signaling pathways as effective therapeutic targets for ischemic and traumatic brain injuries and retinal lesions

Ischemic and traumatic insults to the central nervous system account for most serious acute and fatal brain injuries and are usually characterized by primary and secondary damage.Secondary damage presents the greatest challenge for medical staff;however,there are currently few effective therapeutic targets for secondary damage.Homer proteins are postsynaptic scaffolding proteins that have been implicated in ischemic and traumatic insults to the central nervous system.Homer signaling can exert either positive or negative effects during such insults,depending on the specific subtype of Homer protein.Homer 1b/c couples with other proteins to form postsynaptic densities,which form the basis of synaptic transmission,while Homer 1a expression can be induced by harmful external factors.Homer 1c is used as a unique biomarker to reveal alterations in synaptic connectivity before and during the early stages of apoptosis in retinal ganglion cells,mediated or affected by extracellular or intracellular signaling or cytoskeletal processes.This review summarizes the structural features,related signaling pathways,and diverse roles of Homer proteins in physiological and pathological processes.Upregulating Homer 1a or downregulating Homer 1b/c may play a neuroprotective role in secondary brain injuries.Homer also plays an important role in the formation of photoreceptor synapses.These findings confirm the neuroprotective effects of Homer,and support the future design of therapeutic drug targets or gene therapies for ischemic and traumatic brain injuries and retinal disorders based on Homer proteins.

Scaffold protein RACK1A positively regulates leaf senescence by coordinating the EIN3-miR164-ORE1 transcriptional cascade in Arabidopsis

Plants have adopted versatile scaffold proteins to facilitate the crosstalk between multiple signaling pathways. Leaf senescence is a well-programmed developmental stage that is coordinated by various external and internal signals. However,the functions of plant scaffold proteins in response to senescence signals are not well understood. Here, we report that the scaffold protein RACK1A(RECEPTOR FOR ACTIVATED C KINASE1A) participates in leaf senescence mediated by ethylene signaling via the coordination of the EIN3-miR164-ORE1 transcriptional regulatory cascade. RACK1A is a novel positive regulator of ethylene-mediated leaf senescence. The rack1a mutant exhibits delayed leaf senescence, while transgenic lines overexpressing RACK1A display early leaf senescence. Moreover, RACK1A promotes EIN3(ETHYLENE INSENSITIVE 3) protein accumulation, and directly interacts with EIN3 to enhance its DNA-binding activity. Together, they then associate with the miR164 promoter to inhibit its transcription, leading to the release of the inhibition on downstream ORE1(ORESARA 1) transcription and the promotion of leaf senescence.This study reveals a mechanistic framework by which RACK1A promotes leaf senescence via the EIN3-miR164-ORE1 transcriptional cascade, and provides a paradigm for how scaffold proteins finely tune phytohormone signaling to control plant development.

Rationally designed bioactive milk-derived protein scaffolds enhanced new bone formation

Recently,a number of studies reported that casein was composed of various multifunctional bioactive peptides such as casein phosphopeptide andβ-casochemotide-1 that bind calcium ions and induce macrophage chemotaxis,which is crucial for bone homeostasis and bone fracture repair by cytokines secreted in the process.We hypothesized that the effects of the multifunctional biopeptides in casein would contribute to improving bone regeneration.Thus,we designed a tissue engineering platform that consisted of casein and polyvinyl alcohol,which was a physical-crosslinked scaffold(milk-derived protein;MDP),via simple freeze-thaw cycles and performed surface modification using 3,4-dihydroxy-L-phenylalanine(DOPA),a mussel adhesive protein,for immobilizing adhesive proteins and cytokines for recruiting cells in vivo(MDP-DOPA).Both the MDP and MDP-DOPA groups proved indirectly contribution of macrophages migration as RAW 264.7 cells were highly migrated toward materials by contained bioactive peptides.We implanted MDP and MDP-DOPA in a mouse calvarial defect orthotopic model and evaluated whether MDP-DOPA showed much faster mineral deposition and higher bone density than that of the no-treatment and MDP groups.The MDP-DOPA group showed the accumulation of host M2 macrophages and mesenchymal stem cells(MSCs)around the scaffold,whereas MDP presented mostly M1 macrophages in the early stage.

Overproduction of OsRACK1A,an effector-targeted scaffold protein promoting OsRBOHB-mediated ROS production,confers rice floral resistance to false smut disease without yield penalty

Grain formation is fundamental for crop yield but is vulnerable to abiotic and biotic stresses.Rice grain production is threatened by the false smut fungus Ustilaginoidea virens,which specifically infects rice floral organs,disrupting fertilization and seed formation.However,little is known about the molecular mechanisms of the U.virens-rice interaction and the genetic basis of floral resistance.Here,we report that U.virens secretes a cytoplasmic effector,UvCBP1,to facilitate infection of rice flowers.Mechanistically,UvCBP1 interacts with the rice scaffold protein OsRACK1A and competes its interaction with the reduced nicotinamide adenine dinucleotide phosphate oxidase OsRBOHB,leading to inhibition of reactive oxygen species(ROS)production.Although the analysis of natural variation revealed no OsRACK1A variants that could avoid being targeted by UvCBP1,expression levels of OsRACK1A are correlated with field resistance against U.virens in rice germplasm.Overproduction of OsRACK1A restores the OsRACK1A-OsRBOHB association and promotes OsRBOHB phosphorylation to enhance ROS production,conferring rice floral resistance to U.virens without yield penalty.Taken together,our findings reveal a new pathogenic mechanism mediated by an essential effector from a flower-specific pathogen and provide a valuable genetic resource for balancing disease resistance and crop yield.

MAP Kinases in Immune Responses

MAP kinases are evolutionarily conserved signaling regulators from budding yeast to mammals and play essential roles in both innate and adaptive immune responses.There are three main families of MAPKs in mammals.Each of them has its own activators,inactivators,substrates and scaffolds,which altogether form a fine signaling network in response to different extracellular or intracellular stimulation.In this review,we summarize recent advances in understanding of the regulation of MAP kinases and the roles of MAP kinases in innate and adaptive immune responses.Cellular & Molecular Immunology.2005;2(1):20-27.

Pathogen-inducible OsMPKKI 0.2-OsMPK6 cascade phosphorylates the Raf-like kinase OsEDRI and inhibits its scaffold function to promote rice disease resistance

Mitogen-activated protein kinase(MAPK)cascades regulate a myriad of plant biological processes,including disease resistance.Plant genomes encode a large number of MAPK kinase kinases(MAPKKKs)that can be divided into two subfamilies,namely MEKK-like kinases and Raf-like kinases.Thus far,the func-tions of MEKK-like MAPKKKs have been relatively well characterized,but the roles of Raf-like MAPKKKs in.plant MAPK cascades remain less understood.Here,we report the role of OsEDR1,a Raf-like MAPKKK,in the regulation of the MAPK cascade in rice response tp the bacterial pathogen Xanthomonas oryzae pv.oryzicola(Xoc).We found that OsEDR1 inhibits OsMPKK10.2(a MAPK kinase)activity through physical interaction.Upon Xoc infection,OsMPKK10.2 is phosphorylated at S304 to activate OsMPK6(a MAPK).Interestingly,activated OsMPK6 phosphorylates OsEDR1 at S861,which destabilizes OsEDR1 and thus releases the inhibition of OsMPKK10.2,leading to increased OsMPKK10.2 activity and enhanced resistance of rice plants to Xoc.Taken together,these results provide new insights into the functions of Raf-like ki-nases in the regulation of the MAPK cascade in plant immunity.

Improved L -phenylglycine synthesis by introducing an engineered cofactor self-sufficient system

L-phenylglycine(L-phg)is a valuable non-proteinogenic amino acid used as a precursor to β-lactam antibiotics,antitumor agent taxol and many other pharmaceuticals.L-phg synthesis through microbial bioconversion allows for high enantioselectivity and sustainable production,which will be of great commercial and environmental value compared with organic synthesis methods.In this work,an L-phg synthesis pathway was built in Escher-ichia coli resulting in 0.23 mM L-phg production from 10 mM L-phenylalanine.Then,new hydroxymandelate synthases and hydroxymandelate oxidases were applied in the L-phg synthesis leading to a 5-fold increase in L-phg production.To address 2-oxoglutarate,NH_(4)^(+),and NADH shortage,a cofactor self-sufficient system was introduced,which converted by-product L-glutamate and NAD^(+)to these three cofactors simultaneously.In this way,L-phg increased 2.5-fold to 2.82 mM.Additionally,in order to reduce the loss of these three cofactors,a protein scaffold between synthesis pathway and cofactor regeneration modular was built,which further improved the L-phg production to 3.72 mM with a yield of 0.34 g/g L-phe.This work illustrated a strategy applying for whole-cell biocatalyst converting amino acid to its value-added chiral amine in a cofactor self-sufficient manner.