Distribution of soluble N-ethylmaleimide fusion protein attachment proteins (SNAPS) in the rat nervous system

Soluble N-ethylmaleimide-sensitive fusion protein (NSF) attachment protein (SNAP) plays an essential role in vesicular transport and the release of neurotransmitters and hormones through associations with NSF and SNAP receptors (SNAREs). Three isoforms (α, β and γ) of SNAP are expressed in mammals. We have generated isoform-specific antibodies and studied the expression and distribution of these SNAP isoforms in the rat nervous system. Each antibody specifically recognized α-, β- or γ-SNAP in an isoform-specific manner in immunoblots of brain homogenate. α- And γ-SNAP were ubiquitously expressed in various tissues, whereas β-SNAP was expressed only in brain. After subcellular fractionation of brain homogenates, all three isoforms were recovered in both soluble and particulate fractions. Immunohistochemistry revealed that α- and β-SNAP were generally differentially distributed both in synaptic and non-synaptic regions, including brain white matter. The presynaptic location of both α- and β-SNAP was confirmed by immunoelectron microscopy. At the neuromuscular junction, immunoreactive α-SNAP was identified in synaptic vesicles, while in the cerebellum, β-SNAP was present in the presynaptic membranes of basket neuron and mossy fiber terminals. From these results we suggest that both α- and β-SNAP may play an important role in neurotransmitter release as well as in constitutive vesicular transport.