Cryo-EM structure of the complex between transglutaminase 2 and the 45 kDa domain of fibronectin.

Fibronectin (FN) and transglutaminase 2 (TG2) engage in a high-affinity interaction. This interaction affects anchoring, migration and survival of cells, and high cellular expression of TG2 is associated with metastasis potential of cancers. Previous work has mapped the interaction to involve the N-terminal part of TG2 and an N-terminally located 45 kDa domain of FN (FN45). In particular, the I8 module of FN45 is reported to be necessary and sufficient for TG2 binding. Here, we present the cryo-EM structure of a complex between human TG2 and FN45 at 2.8 Å resolution. In the structure, the distal region of the TG2 N-terminal domain binds the FN45 I8 module, whereas the proximal N-terminal region and adjacent catalytic core segment bind the FN45 I7 module and, to a lesser extent, the FN45 II2 module. The FN45 I7 and FN45 I8 modules have about equal buried surface areas in their interaction with TG2. A glycine residue at position 127 of TG2 is crucial for interaction with Trp553 of the FN45 I8 module. Mutation of this residue to isoleucine, which is carried by transglutaminase 3 that does not bind FN45, abrogates the binding of FN45 to TG2. This finding suggests that the interaction of the FN45 I7 module with TG2 is contingent on the FN45 I8 module making an interaction with TG2. Further, this finding highlights the region surrounding residue 127 of TG2 as a promising target for structure-based design of anticancer drugs aimed at disrupting the TG2-FN interaction.