Further analyses of APRIL/APRIL-receptor/glycosaminoglycan interactions by biochemical assays linked to computational studies

A proliferation-inducing ligand (APRIL) is a member of the tumor necrosis factor superfamily. APRIL is quite unique in this superfamily for at least for two reasons: (i) it binds to glycosaminoglycans (GAGs) via its positively charged N-terminus; (ii) one of its signaling receptors, the transmembrane activator and CAML interactor (TACI), was also reported to bind GAGs. Here, as provided by biochemical evidences with the use of an APRIL deletion mutant linked to computational studies, APRIL-GAG interaction involved other regions than the APRIL N-terminus. Preferential interaction of APRIL with heparin followed by chondroitin sulfate E was confirmed by in silico analysis. Both computational and experimental approaches did not reveal the heparan sulfate binding to TACI. Together, computational results corroborated experiments contributing with atomistic details to the knowledge on this biologically relevant trimolecular system. Additionally, a rigorous highthroughput analysis of the free energy calculations data was performed to critically evaluate the applied computational methodologies.