Identification of an amelin isoform located in axons

A new axonal isoform of amelin, an analogue of the erythrocyte spectrin binding protein termed protein 4.1 has been identified in mouse brain. This new isoform has a molecular weight of 93 kDa, and migrates to a more acidic pH (pH 7.5-8.0) than the previously described amelin E (pH 8.5) on two dimensional NEPHGE-SDS PAGE. The 93 kDa protein looks nearly identical to amelin E on two dimensional chymotryptic iodopeptide mapping, and both share partial homology with rbc protein 4.1. The new isoform is located in axons, and the soma of neurons in mouse cerebellum, while amelin E is located in neuronal soma and dendrites. The axonal amelin antibody detects a 97 kDa protein in embryonic tissue which diminishes during development; and a 93 kDa protein which is first seen at postnatal day 1 of mouse brain ontogeny, increasing constantly to its adult concentrations. This time course of expression is quite different than amelin E, which is present at embryonic day 15 and diminishes constantly reaching its lowest concentration in the adult brain. We hypothesize that axonal amelin and amelin E may play important roles in the interaction of brain spectrin(240/235) and brain spectrin(240/235E) with f-actin and neuronal membranes.