S100beta inhibits the phosphorylation of the L-MAG cytoplasmic domain by PKA.
The myelin-associated glycoprotein (MAG) is a cell adhesion molecule expressed by myelinating glia, existing as two isoforms that differ only by their cytoplasmic domains. We have studied the in vitro phosphorylation of recombinant rat MAG cytoplasmic domains by three kinases for which consensus sequences exist within this domain, revealing phosphorylation of the L-MAG-specific domain by protein kinase A (PKA). Phosphorylation of the L-MAG cytoplasmic domain by PKA was decreased in the presence of S100beta, providing a functional significance to the interaction between L-MAG and S100beta, and further indicating that L-MAG may play a role in myelinating glial cell signalling processes.