Downstream of Ras is a highly conserved cascade of three protein kinases-

Ras → Raf → MEK → MAP kinase

TLS Online TPP Program

#Id: 9618

#XL - T Zoology

Neuregulins 1, 2, 3, and 4, bind to HER4 that, like HER1, can also form homodimers.

TLS Online TPP Program

#Id: 9619

#XL - T Zoology

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)

TLS Online TPP Program

#Id: 9620

#XL - T Zoology

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

TLS Online TPP Program

#Id: 9621

#XL - T Zoology

Kinase domains typically contain two regions:

N and C lobes

TLS Online TPP Program

#Id: 9622

#XL - T Zoology

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

TLS Online TPP Program

#Id: 9623

#XL - T Zoology

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