Lys & Arg have four ionisations zones

1. 1--------pK1 – charge +2

2. pK1---------pK2 charge +1

3. pK2---------pKr charge 0

4. pKr---------14 charge -1

TLS Online TPP Program

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#XL - T Zoology

Most cells lack RIII, TGF-β binds directly to the RII

dimer, but Active RII kinase activity is not sufficient to generate an intracellular signal

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#XL - T Zoology

RI will not bind to RII unless RII is bound to TGF-β.

TLS Online TPP Program

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#XL - T Zoology

RII phosphorylates serine and threonine in the juxtamembrane segment of the RI (ligand induced receptor hetero-oligomerization), releasing the inhibition of RI kinase activity.

TLS Online TPP Program

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#XL - T Zoology

Active type I receptor kinase phosphorylates a Smad

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#XL - T Zoology

Three types of Smad proteins function in the TGF-β signaling pathway: 

R-Smads (Smad2 and Smad3)

Co-Smads (Smad4)

I-Smads (Smad7)

TLS Online TPP Program

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#XL - T Zoology

Smad2/3 become phosphorylated by active RI receptors and together with Smad4 move into the nucleus to activate gene transcription