Role Of Effector Molecules Research Articles

The Role of Cd28 Costimulatory Receptors in Signalling Pathways

Naive T cells require extracellular stimulus signals through the T-cell receptor cascade (TCR). This TCR then recognized the antigens present on the molecules of the major histocompatibility complex (MHC) using the CD4 and CD8 receptor. Upon recognition, TCR- induced signal transduction propagates signals through different molecules and induced secondary signalling. Consequently, intracellular signaling cascades determine the characteristics of immune responses mediated by T- cells. Consequently, rigorous regulation of T-cell activation is crucial for T-cell homeostasis and appropriate immune responses. Dysregulation of TCR signalling can result in energy or autoimmunity. In this review article, we summarize current knowledge on the signalling pathways that govern how the TCR complex transmits signals into cells and the roles of effector molecules that are involved in these pathways.

DsEcp2-1 is a polymorphic effector that restricts growth of Dothistroma septosporum in pine

The detrimental effect of fungal pathogens on forest trees is an increasingly important problem that has implications for the health of our planet. Despite this, the study of molecular plant-microbe interactions in forest trees is in its infancy, and very little is known about the roles of effector molecules from forest pathogens. Dothistroma septosporum causes a devastating needle blight disease of pines, and intriguingly, is closely related to Cladosporium fulvum, a tomato pathogen in which pioneering effector biology studies have been carried out. Here, we studied D. septosporum effectors that are shared with C. fulvum, by comparing gene sequences from global isolates of D. septosporum and assessing effector function in both host and non-host plants. Many of the effectors were predicted to be non-functional in D. septosporum due to their pseudogenization or low expression in planta, suggesting adaptation to lifestyle and host. Effector sequences were polymorphic among a global collection of D. septosporum isolates, but there was no evidence for positive selection. The DsEcp2-1 effector elicited cell death in the non-host plant Nicotiana tabacum, whilst D. septosporum DsEcp2-1 mutants showed increased colonization of pine needles. Together these results suggest that DsEcp2-1 might be recognized by an immune receptor in both angiosperm and gymnosperm plants. This work may lead to the identification of plant targets for DsEcp2-1 that will provide much needed information on the molecular basis of gymnosperm-pathogen interactions in forests, and may also lead to novel methods of disease control.

The role of effector molecules in signal transduction by PII proteins

PII proteins are one of the most widely distributed signal transduction proteins in Nature, being ubiquitous in bacteria, archaea and plants. They act by protein-protein interaction to control the activities of a wide range of enzymes, transcription factors and transport proteins, the great majority of which are involved in cellular nitrogen metabolism. The regulatory activities of PII proteins are mediated through their ability to bind the key effector metabolites 2-OG (2-oxoglutarate), ATP and ADP. However, the molecular basis of these regulatory effects remains unclear. Recent advances in the solution of the crystal structures of PII proteins complexed with some of their target proteins, as well as the identification of the ATP/ADP- and 2-OG-binding sites, have improved our understanding of their mode of action. In all of the complex structures solved to date, the flexible T-loops of PII facilitate interaction with the target protein. The effector molecules appear to play a key role in modulating the conformation of the T-loops and thereby regulating the interactions between PII and its targets.

The role of effector molecules in regulating ribulosebisphosphate carboxylase activity

Ribulosebisphosphate carboxylase can exist in two forms having different kinetic properties. The fraction of enzyme present in each of the two forms is determined by both the absolute and the relative amounts of substrates and other effector molecules in solution with the enzyme. High CO 2 levels induce formation of an active CO 2 form of the enzyme while high ribulosebisphosphate (RuBP) levels cause formation of a much less active form. The CO 2 form is characterized by a high K m(RuBP) , low K m(CO 2) , and relatively high V. The ribulosebisphosphate form has comparatively lower K m(RuBP) and V and higher K m(CO 2) . CO 2 appears to bind before RuBP in the reaction sequence catalyzed by the CO 2 form; this catalytic binding order is apparently reversed in the RuBP form. Steady state rates of enzyme reaction reflect the contributions of both these forms. A brief model, based on the cooperative effects of binding at a small number of catalytic or activator sites in the multimeric enzyme, is presented to account for the changes in enzyme activity with varying substrate and effector molecule concentrations.