Size of aquaporin-4 orthogonal arrays of particles are affected by the palmitoylation state of the M1 isoform

Human aquaporin-4 (AQP4) is a water-channel protein crucial for water-ion homeostasis in the central nervous system. Dysregulation of AQP4 function is linked to neurological conditions like brain edema, neuromyelitis optica, and epilepsy. AQP4 has two isoforms, M1 and M23. The M23 isoform forms large structures known as Orthogonal Arrays of Particles (OAPs), while M1 coats the outer surface of OAPs. The dynamics of OAP aggregation may modulate water permeability and ion homeostasis in the brain. This study shows that the palmitoylation state of M1 influences OAP self-assembly, with depalmitoylated M1 producing OAPs 20 % larger than those formed by palmitoylated M1 at the same concentration. This, along with prior research on M1 aggregation, suggests palmitoylated M1 forms a single outer layer arounf OPAs, whereas depalmitoylated M1 creates a double layer. Single-particle tracking was used to study M23 OAP formation in lipid bilayers under equilibrium conditions. Our data support the idea that M1 regulates M23 OAP size, showing that average OAP size decreases as M1 concentration increases. This study explores the inhibitory effects of M1 on AQP4 M23 assembly and how M1's palmitoylation state affects OAP size regulation. These insights could lead to new therapeutic approaches for managing AQP4 assembly and function in related conditions.