RTK Receptor
Protein kinases are a class of enzymes that have a catalytic component that transfers the gamma (terminal) phosphate from nucleoside triphosphates (typically ATP) to one or more amino acid residues in the side-chain of a protein substrate, causing a conformational change that affects protein activity. The enzymes are divided into two groups based on substrate specificity: serine/threonine-specific and tyrosine-specific.
Structure
Protein kinase domains are found in protein tyrosine kinase proteins and consist of an N-terminal lobe with 5 beta-sheet strands and an alpha helix termed the C-helix, as well as a C-terminal domain with 6 alpha helices (helices D, E, F, G, H, and I). Catalysis is controlled by two loops in the kinase domain’s core. The HRD motif can be found in the catalytic loop (usually with sequence His-Arg-Asp). During catalysis, the aspartic acid of this motif creates a hydrogen bond with the substrate OH group on Tyr. The activation loop, whose location and conformation determine whether the kinase is active or inactive, is the other loop. The DFG motif starts the activation loop (usually with the sequence Asp-Phe-Gly). The Protein Data Bank contains about 1500 3D structures of tyrosine kinases. PDB: 1IRK, the crystal structure of the human insulin receptor’s tyrosine kinase domain, is one example.
Serine/Threonine-specific
A serine/threonine protein kinase enzyme phosphorylates the OH group of serine or threonine amino-acid residues with similar side chains. Serin/threonine kinases account for at least 350 of the 500 or so human protein kinases (STK). A transferase enzyme that transfers phosphates to the oxygen atom of a protein’s serine or threonine side chain is known as a serine/threonine protein kinase. This process is known as phosphorylation. Protein phosphorylation, in particular, is a critical posttranslational alteration that is involved in a variety of biological functions.
Receptor Tyrosine Kinase Signaling
Cell signalling is a cell’s capacity to accept, process, and transmit messages to its surroundings and to itself. Cell signalling is a basic characteristic of all prokaryotic and eukaryotic cellular life. Extracellular signals (or signals that originate outside of a cell) can be physical agents such as mechanical pressure, electricity, temperature, light, or chemical signals (e.g., small molecules, peptides, or gas).