Comparison of Target Recognition by TRAF1 and TRAF2

Abstract

Although TRAF1 and TRAF2 share common receptors and have extremely conserved amino acid residues, recent studies have shown that key differences in receptor binding preferences with different affinities exist, which might be important for their different functions in TRAF-mediated signal transduction. To better understand TRAF1 and TRAF2 signaling, we analyzed and compared their receptor binding-affinities. Our study revealed that TRADD, TANK, and caspase-2 bind to both TRAF1 and TRAF2 with different affinities in vitro. Sequence and structural analyses revealed that S454 on TRAF2 (corresponding to A369 of TRAF1) is critical for the binding of TRADD, and F347 on TRAF1 (corresponding to L432 of TRAF2) is a critical determinant for high affinity binding of TANK and caspase-2.Int. J. Mol. Sci. 2020, 21, 2895 2 of 12 ubiquitin ligase [23]. Even without E3 ubiquitin ligase activity, anti-and pro-apoptotic functions of TRAF1 have been discovered in immune and neuronal cells, respectively [24,25]. The role of TRAF1 as a positive regulator in insulin resistance and hepatic steatosis was also recently highlighted [26].All TRAFs, except TRAF7, contain a protein-interacting domain, the TRAF domain, at their C-terminus, which is divided into two distinct regions, a TRAF-N coiled-coil and TRAF-C globular subdomain (Figure 1a). Structural studies of the TRAF domains of TRAF1 [27], TRAF2 [28], TRAF3 [29], TRAF4 [30,31], TRAF5 [29], and TRAF6 [2] have revealed that the globular subdomain is composed of seven to eight anti-parallel β-sheet folds (Figure 1b). The functional organization of the TRAF domains comprise mushroom-like trimeric structures [3]. Despite their sequence and structural similarities, each TRAF has its own binding-partner specificity. Although TRAF4 and TRAF6 recognize completely different sequences, it is well established that TRAF1-3 and 5 share almost the same binding motifs.

The structure of TRAF7 coiled-coil trimer provides insight into its function in zebrafish embryonic development

“…We then explored the detailed mechanism of trimerization at the atomic level. The comparison of CC domain structures of TRAF family members, which were collected from the Protein Data Bank archive (PDB) or computationally generated by AlphaFold ( Kim and Park, 2020 ), revealed that TRAF7 has a long CC region similar to TRAF1/2 CC region ( Supplementary Figure S4 ), indicating the potential for occupying a significant space and engaging in interactions with other proteins.…”