Challenging AQP4 druggability for NMO-IgG antibody binding using molecular dynamics and molecular interaction fields

Abstract

Neuromyelitis optica (NMO) is a multiple sclerosis-like immunopathology disease affecting optic nerves and the spinal cord. Its pathological hallmark is the deposition of a typical immunoglobulin, called NMO-IgG, against the water channel Aquaporin-4 (AQP4). Preventing NMO-IgG binding would represent a valuable molecular strategy for a focused NMO therapy. The recent observation that aspartate in position 69 (D69) is determinant for the formation of NMO-IgG epitopes prompted us to carry out intensive Molecular Dynamics (MD) studies on a number of single-point AQP4 mutants. Here, we report a domino effect originating from the point mutation at position 69: we find that the side chain of T62 is reoriented far from its expected position leaning on the lumen of the pore. More importantly, the strength of the H-bond interaction between L53 and T56, at the basis of the loop A, is substantially weakened. These events represent important pieces of a clear-cut mechanistic rationale behind the failure of the NMO-IgG binding, while the water channel function as well as the propensity to aggregate into OAPs remains unaltered. The molecular interaction fields (MIF)-based analysis of cavities complemented MD findings indicating a putative binding site comprising the same residues determining epitope reorganization. In this respect, docking studies unveiled an intriguing perspective to address the future design of small drug-like compounds against NMO. In agreement with recent experimental observations, the present study is the first computational attempt to elucidate NMO-IgG binding at the molecular level, as well as a first effort toward a less elusive AQP4 druggability.

Comparative molecular dynamics study of neuromyelitis optica-immunoglobulin G binding to aquaporin-4 extracellular domains

“…Such trends are observed also when the two computed C-alpha distances (monomer A vs. B and monomer C vs. D) are considered separately. Taken together, these observations support the key role of T62 as representative of the loop A conformation, in agreement with prior studies [29,30,50]. …”

“…1). Following an approach used before to investigate the conformational effect of mutations in AQP4 [30], we analyzed the distances of alpha carbon atoms averaged along the four monomers (C-alpha AV ). We note that the AQP4 tetramer is axially-symmetric with respect to the z-axis passing through the central pore, as depicted in Fig.…”

“…We recently showed [30] that an alteration of the conformation of residues located in the TM2 region is able to alter the conformation of the entire loop A, hence impairing the formation of the NMO-IgG epitope. Fig.…”

“…All simulations were performed on the FERMI supercomputer at CINECA, Italy. Following a previously applied protocol [30,47], the Root Mean Square Fluctuation (RMSF) were calculated over all the simulated systems upon alignment of the trajectory to all the C-alpha atoms belonging to the monomer under investigation.…”

Effects of Mutations on Structure–Function Relationships of Matrix Metalloproteinase-1

“…Mutations can influence not only the local structure, but also regions which are distant from the mutation sites [19]. In order to explore these effects we analyzed the distance between the THP scissile bond and the catalytic Zn 2+ in all mutants and the WT (Table S3; Figure 4).…”