phosphorelay signal transduction system

Definition

Target type: biologicalprocess

A conserved series of molecular signals found in prokaryotes and eukaryotes; involves autophosphorylation of a histidine kinase and the transfer of the phosphate group to an aspartate that then acts as a phospho-donor to response regulator proteins. [PMID:9191038]

The phosphorelay signal transduction system is a complex and highly conserved mechanism used by bacteria, plants, and some eukaryotic organisms to relay signals across cellular compartments. It involves a series of phosphorylation events, where a phosphate group is transferred from one protein to another, ultimately leading to the activation of specific target proteins. Here's a detailed description of the process:

**1. Sensor Kinase Activation:**
The process starts with the activation of a sensor kinase, a transmembrane protein embedded in the cell membrane. These kinases typically have two domains: a sensory domain exposed to the external environment and a catalytic kinase domain located in the cytoplasm. When the sensor kinase detects a specific environmental signal, such as changes in nutrient availability, osmotic pressure, or stress, it undergoes a conformational change. This change activates the kinase domain, enabling it to autophosphorylate itself on a conserved histidine residue.

**2. Phosphate Transfer to a Histidine Phosphotransfer Protein:**
Once the sensor kinase is phosphorylated, it transfers the phosphate group to a second protein called a histidine phosphotransfer protein (Hpt). Hpt is a soluble protein that acts as a mobile phosphate carrier. The phosphate group is transferred from the histidine residue on the sensor kinase to a conserved histidine residue on the Hpt protein.

**3. Phosphate Transfer to a Response Regulator:**
The phosphorylated Hpt protein then interacts with a response regulator protein, typically located in the cytoplasm. The response regulator also contains a conserved histidine residue, but it can also be phosphorylated on a conserved aspartate residue. The phosphate group is transferred from the histidine residue of Hpt to the aspartate residue of the response regulator.

**4. Response Regulator Activation and Target Protein Regulation:**
Phosphorylation of the response regulator activates its function, often by triggering a conformational change. This activated response regulator can then interact with and regulate downstream target proteins, such as transcription factors, enzymes, or other signaling molecules. The specific target protein and the nature of its regulation depend on the particular phosphorelay system.

**5. Signal Deactivation:**
To ensure proper signal transduction and prevent continuous activation, the phosphorelay system includes mechanisms for signal deactivation. This typically involves the action of phosphatases that remove the phosphate group from the phosphorylated proteins, resetting the system to its inactive state.

**Overall, the phosphorelay signal transduction system functions as a complex molecular switch that allows organisms to respond to environmental cues and regulate cellular processes. The system is highly versatile, enabling organisms to adapt to various stimuli and maintain cellular homeostasis.**'
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Proteins (1)

Compounds (1)