Characterization of the relative binding
affinities of TRAFs 2, 3, 5, and 6 for the CD40 cytoplasmic tail and
determination of the minimal binding regions within the CD40 C17
region. (A) TRAFs 2 and 3 bind to the CD40ct with much
greater affinity than TRAFs 5 and 6. The same amount of glutathione
beads bound with the GST-mouse CD40ct fusion protein was incubated with
extracts from 293T cells transfected with pEBB-Flu TRAF2, pEBB-Flu
TRAF3, pEBB-Flu TRAF5, or pEBB-Flu TRAF6. The beads were washed, and
bound proteins were detected by Western blot analysis with anti-Flu
antibodies (Fig. 1A Upper). Equal
amounts of extracts (5% of input used for GST pull-down) were analyzed
by Western blot analysis with anti-Flu antibodies to ensure similar
levels of expression of the different Flu-tagged TRAFs (Fig.
1A Lower). (B) The
minimum binding regions of TRAF2 and TRAF3 within the C17 region are
different. Lysates from 293T cells expressing Flu-TRAF2 or Flu-TRAF3
were incubated with GST, GST-C17, GST-C10N, or GST-C10C fusion proteins
immobilized on glutathione beads. The bound proteins then were analyzed
by Western blot analysis with anti-Flu antibodies.