NEU1NEU4

NEU1NEU4 is not a single gene or protein, but a way to refer to the two human neuraminidase (sialidase) genes NEU1 and NEU4 together. Both encode enzymes that remove terminal sialic acid residues from glycoproteins, glycolipids, and gangliosides, contributing to the remodeling of glycoconjugates and the regulation of cell signaling, adhesion, and trafficking.

NEU1 encodes neuraminidase 1, a lysosomal enzyme that functions as part of a multienzyme complex with protective protein cathepsin A (CTSA). This complex stabilizes NEU1 and supports its lysosomal activity, where it participates in the degradation of sialoglycoconjugates. NEU1 is broadly expressed, with pronounced activity in tissues such as liver, spleen, and brain. Deficiency of NEU1 causes sialidosis, a lysosomal storage disorder characterized by accumulation of sialoglycoconjugates, with clinical forms ranging from later-onset myoclonus and ataxia (type I) to severe congenital disease (type II).

NEU4 encodes neuraminidase 4, a more versatile sialidase found in multiple isoforms that can localize to lysosomes and mitochondria, and sometimes associate with other intracellular compartments. NEU4 is capable of desialylating a range of substrates, including gangliosides and glycoproteins, and may function at both acidic and near-neutral pH in different cellular contexts. In experimental systems, NEU4 has been linked to roles in cellular differentiation, apoptosis, and cancer cell behavior, but its involvement in a specific heritable human disorder has not been established.

Together, NEU1 and NEU4 represent distinct yet related components of the cellular sialic acid remodeling machinery. They exhibit different subcellular localizations, pH optima, and substrate preferences, reflecting their specialized physiological roles. Research continues to clarify their precise functions in health and disease.