Postsynaptic MAGUK scaffold supercomplexes exhibit nanometer-scale proximity that varies systematically across brain regions, undergoes dynamic remodeling during postnatal development and aging, and is governed by competitive interactions among different MAGUK family members, with genetic disruption of individual scaffolds triggering brain-wide reorganization of this nanoscale architecture that links to synaptic stability and neuropsychiatric disease risk.

How biological complexity emerges from the ordered assembly of molecular building blocks into supramolecular systems remains a central question, particularly in the mammalian brain with its vast synaptic diversity. We introduce NanoSYNMAP, a genetic, optical, and computational platform that integrates FRET with synaptome mapping to quantify nanoscale proximity of proteins in individual synapses brain-wide. We generate the first brain atlas of synaptic nanoarchitecture, based on the proximity of postsynaptic MAGUK supercomplexes. This reveals a molecular logic in which spacing of supramolecular assemblies specifies nanoscale architecture that organizes the global synaptome architecture. Nanoarchitecture varies across brain regions, differentiates during postnatal development, and remodels with aging. Supercomplex proximity reflects scaffold abundance, nanodomain organization, and competitive interactions among MAGUK assemblies. Deletion of a neuropsychiatric risk gene triggers widespread reorganization of nanoscale architecture. These findings establish molecular proximity as a fundamental scalable dimension of synapse diversity in health and disease.