Metalloprotease MP100: a synaptic protease in rat brain.

Proteases are expressed widely throughout the nervous system and perform essential functions. We have earlier characterized and cloned the metalloprotease MP100, an enzyme originally described as a beta-amyloid precursor protein (beta-APP) processing candidate. In the present study we describe the cellular and subcellular localization of MP100 in rat brain. A punctuate intracellular immunostaining in cortical, hippocampal and cerebellar neurons suggests its high abundance in vesicular intracellular structures. The MP100 staining pattern resembled that of the presynaptic protein synaptophysin. In gel filtration chromatography of isolated rat brain synaptosomal membranes, MP100 co-fractionated with synaptophysin and beta-APP. Furthermore, pre-embedding immunoelectron microscopy of the cerebellum revealed MP100 to be localized at synaptic sites. All together, these data might indicate a role for MP100 in functions such as proteolytic modification of synaptic proteins.