Chapter 55 - Transmembrane Receptor Oligomerization

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This chapter provides a brief description on how oligomerization is utilized by the major cell transmembrane receptor classes. The cell-surface receptors possessing intrinsic tyrosine kinase activity (RTK) minimally require a dimeric state for their full activity. RTK dimerization occurs as a result of ligand binding, and the ligand-bound monomer then recruits another monomer into the complex, allowing for the interaction of the kinase domains and their subsequent transphosphorylation. The initial phosphorylation events usually occur on the activation loop and help stabilize the open conformation, thereby allowing access of adenosine triphosphate (ATP) and substrate to their respective binding sites within the kinase domain. The cytokine receptors are composed of numerous kinds of transmembrane receptors that are characterized by conserved patterns of amino acid residues in their ectodomains and the lack of enzymatic activity within their endodomains. They associate with non-receptor tyrosine kinases such as the Janus kinases (JAK) or Src family kinases. The class I cytokine receptors are the growth hormone receptor (GHR) and erythropoietin receptor (EPOR) that function as homodimers. EPOR appears to exist at the cell surface as an inactive dimer and this state is mediated by the transmembrane domain. Type II cytokine receptors consist primarily of receptors for interferons and interleukin-10 (IL-10). The receptors for interferon-γ (IFNγR) and IL-10 (IL-10R) have a similar structure in that they are each composed of two type 1 receptors and two type 2 receptors forming a heterotetramer.

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