Domain‐Level Interaction of <scp>FAP174</scp> ( <scp>MYCBP</scp> ‐1) and <scp>FAP147</scp> ( <scp>MYCBPAP</scp> ) Proteins of the C2a Projection of <i>Chlamydomonas</i> Cilia

The C2a projection of the central pair of flagella in Chlamydomonas reinhardtii harbours the A-kinase anchoring protein FAP65, FAP174, FAP147 and FAP70. FAP174, an RII-like protein with its N-terminal dimerization and docking domain, binds to the amphipathic helices of FAP65. Cryo-EM data do not reveal the entire sequences for FAP174 and FAP147. Hence, the interacting domains within this scaffold remain elusive. This study has identified the interacting domains of FAP174 with FAP147. The FAP147 protein and its MYCBPAP domain (129-639 a.a.) bind to the C-terminus of FAP174 (47-92 a.a.). In silico docking analyses using CABS-Dock to delineate the interaction identified several MYCBPAP-derived peptides, such as p3 (310-339), p4 (319-348), p9 (547-576), p13 (528-557) and p15 (350-379), to form stable interacting complexes with RMSD < 3 Å 2-3 times, and are potentially amphipathic. To gain atomistic details of the interaction, molecular dynamics (MD) simulations of the FAP147 MYCBPAP domain in complex with the FAP174 C-terminus were performed. It revealed stable interfacial contacts, a subset of which overlap with residues within the p15 peptide region of the MYCBPAP domain, while identifying G48, S49, P52, Y55, L79, Q80 and V83 as key interacting residues within the C-terminus of FAP174. Individual alanine substitution of the FAP174 residues, followed by overlay assay with FAP147, retained the interaction, indicating that the interaction does not depend solely on discrete amino acids but on broader interface interactions.