PEPR 1 and PEPR2 (Perception of the Arabidopsis Danger Signal Peptide 1 or 2) are homolog kinases that act as enzymes on other proteins. They attach a phosphate group to specific proteins, called phosphorylation. These reactions can cause the function of the phosphorylated proteins to change. Both PEPR 1 and PEPR 2 can be classified as receptor kinases, which serve an important role in immunity in plants. Receptor kinases have the ability to change the conformation of receptors by adding the phosphate group. These specific receptor kinases serve as a pattern recognition receptor, or PRR, that can quickly and efficiently recognize many different molecular patterns or signatures that are unique to each pathogen. They can also detect different danger signals released from the host and respond accordingly. More specifically, the proteins contain leucine-rich repeat segments that interact outside of the cell. This leucine-rich repeat is a structural motif present in some proteins that has specific functions due to its folded structure. This fold can contain many repeating amino acids, but the most common is the hydrophobic leucine, hence the name. PEPR1 and PEPR2 are present in plants and are involved in several immune system processes. Their ability to change the conformation of receptors can have an effect on signaling processes within plants, allowing the plant to have a system of immunity in place in case of an infection or pathogen.
Discovery
The PEPR1 and PEPR2 kinases that bind to the receptors AtPEPR1 and AtPEPR2, respectively were identified. Through photolabeling with a radioactively marked ligand, an AtPep1 receptor was able to be purified and later duplicated. This led to the discovery of the first damage associated molecular pattern or DAMP/pattern recognition receptor couple in Arabidopsis, otherwise known as the thale cress, which is a small flowering plant common in Eurasia. This discovered receptor was coined PEPR1, PEP receptor 1. Further analysis of the Arabidopsis genome established a very genetically similar homologue of PEPR1, PEPR2, or PEP receptor 2.
Research
PEPR 1 and PEPR2 have been studied by multiple researchers for their properties and functions in immune system processes. Many of these studies involve isolating and crystallizing the proteins and have been performed in the natural setting, in vivo, as well as in an artificial lab environment, in vitro. The proteins function as inhibitors that potentially help plants have immunity to different substances by working with other compounds in the plant. Pep1, a receptor in the plant, can be controlled by PEPR1 and PEPR2, along with other proteins and enzymes such as “botrytis-induced kinase 1 (BIK1) and PBS1-like 1 (PBL1)”. More specifically, when exposed to the Pep1 receptor, the proteins act as kinases when interacting with BIK1.
Function
The receptor kinase properties of PEPR1 and PEPR2 allow them to perform important duties within plants. Plants have complex and detailed signaling systems, and receptor kinases ensure that these systems function properly. The receptor kinases recognize elements associated with pathogens that interact with the plant to ensure that the plant can protect itself from foreign, harmful substances. Using these properties, receptor kinases are very important in the immune system of a plant.
PEPR 1 and PEPR 2 are homologs, meaning they have similar properties and structures, yet they have distinguishing reactions when exposed to different compounds. For example, both kinases act as receptors of AtPeps. However, they respond to the compound differently. The kinases each preferentially interact with a different AtPep, giving them unique functions depending on their environments. According to research done on PEPR1 and PEPR2, their function is very important not only in immunity, but in important signaling pathways as well, such as the jasmonic acid-ethylene pathway and the salicylic acid pathways. These unique responses may make it possible for PEPR 1 and PEPR 2 to be a link between both "local and systemic immunity" systems.
Structure
PEPR1 and PEPR2 share a unique structural component because they contain extracellular leucine-rich repeat motifs (LRR motifs). Studies have been conducted to discover the structure of PEPR1 or PEPR2, sometimes in complex with certain proteins and in specific environments. When complexed with AtPep1, it forms a crystalline structure in which the units contain two copies of PEPR1 and AtPep1 and are not symmetrical. In this complex, PEPR1 does not oligomerize as some other protein receptors would. The receptor kinase also contains a leucine rich repeat section that consists of 27 repeats.
