The three known RLRs (RIG-I, MDA5, and LGP2) are CARD-containing RNA helicases that recognize viral RNAs, usually from RNA viruses such as influenza, measles, and West Nile.

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#Id: 9619

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HER2 (mouse Erb-B2), cannot bind any ligand, it can form a heterodimer with ligand-activated HER1, HER3, or HER4 (Erb-B1, 3, or 4)

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HER3 (Erb-B3) can bind ligands but lacks a functional kinase domain and can signal only when heterodimerizes with HER2 (Erb-B2

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#Id: 9621

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Kinase domains typically contain two regions:

N and C lobes

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Monomeric state of the EGF receptor,

activation loop is situated in the active site of the kinase near the interface of the N and C lobes, blocking the site’s activity; in this way the kinase is maintained in the inactive or “off” state

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Asymmetric kinase dimer 

Receptor dimerization brings the kinase domains of the two subunits close together, so that the C lobe of one kinase domain binds to the N lobe of the other kinase domain

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#Id: 9624

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Two Mechanisms Down-Regulate Signaling from RTKs

1. Phosphotyrosine phosphatases

2. Receptor-mediated endocytosis followed by degradation in lysosomes