Dissection of the CD40ct by alanine-scanning
mutagenesis. (A and B) TRAF2 and TRAF3
contact overlapping but different sets of amino acid residues in the
CD40ct. The same amount of GST protein and GST fusion proteins
containing either wild-type C17 or one of 17 mutated forms of C17, with
1 aa residue replaced by alanine, was incubated with 293T cell extracts
overexpressing Flu-tagged TRAF2 (A) or TRAF3 (B).
The bound Flu-TRAF2 and Flu-TRAF3 were detected by Western blot
analysis using anti-Flu antibody. (C) The hydroxyl group of
the threonine at position 234 is essential for TRAF binding. The same
amounts of GST protein and GST fusion proteins containing wild-type
C17, T234A, T234S, and T234V were incubated with 293T cell extracts
overexpressing Flu-tagged TRAF2 and TRAF3. The bound Flu-TRAF2 and
Flu-TRAF3 were detected by Western blot analysis using anti-Flu
antibody.