The expression of recombinant large myelin-associated glycoprotein cytoplasmic domain and the purification of native myelin-associated glycoprotein from rat brain and peripheral nerve

The myelin-associated glycoprotein (MAG) is a transmembrane protein of the immunoglobulin superfamily existing as two isoforms (L-MAG and S-MAG) that are differentially expressed by myelinating glial cells of the central and peripheral nervous systems, where MAG represents 1 and 0.1% of the total my elin proteins, respectively. The polypeptide chains of the two isoforms dif fer only by the carboxy terminus of their respective cytoplasmic domains, w hich most probably determine the isoform-specific functions. Here, we descr ibe the expression of the L-MAG cytoplasmic domain as a GST fusion protein. The recombinant protein was used to raise polyclonal antibodies against th e L-MAG-specific carboxy terminus and against the region of the MAG cytopla smic domain common to both S-MAG and L-MAG. These antibodies, which functio n in dot blotting; Western blotting, and immunoprecipitation, were used to immunopurify native MAG from both rat brain and peripheral nerves in quanti ties and purity sufficient for the realization of most biochemical and func tional studies. The antibodies and the recombinant and native MAG; proteins provide much needed tools for the study of the common and isoform-specific properties and functions of L-MAG and S-MAG. (C) 1999 Academic Press.