Binding Interaction Between Two Mutant Myocilin Olfactomedin Domain Monomers in a Homodimer

In myocilin-associated glaucoma, pathogenic missense mutations accumulate mainly in the olfactomedin domain (mOLF) of myocilin. This makes the protein susceptible to aggregation, where mOLF-mOLF dimerization is possibly an initial stage. Nevertheless, there are no molecular level studies that have probed the nature of interactions occurring between two mOLF domains and the key characteristics of the resulting dimer complex. In this work, we used AlphaFold2 to obtain an I477N mutant mOLF structure with high quality followed by a stable I477N mOLF-mOLF homodimer model using molecular docking combined with molecular dynamics simulations. Moreover, molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) methods coupled with per-residue energy decomposition studies are carried out to identify the key residues involved in the binding interaction. Based on these results, we provide insights into the molecular level understanding of the intermolecular interaction between two mOLF domains in an I477N homodimer. Hydrogen bonds, salt bridges, and favorable van der Waals interactions are observed in the binding interface of the homodimer. Additionally, our results suggest that I477N mutant mOLF aggregation could be a multistep process, beginning with an initial mOLF-mOLF dimerization mainly mediated by residues such as Asp395 and Arg681. Also, the peptides P1 (residues 326-337) and P3 (residues 426-442) of the mOLF domain, previously identified as pertinent for myocilin aggregation, could potentially contribute to a subsequent stage of myocilin aggregation, the first step being mOLF-mOLF dimerization.