Structure of P0 protein: Homology to immunoglobulin superfamily

Homology of the P0 protein to the immunoglobulin-cell adhesion molecule superfamily was examined by comparing their amino acid sequences. The predicted secondary structure of the amino-terminal domain of P0 protein was suggested to be similar to all immunoglobulin domains consisting of two β-sheets with antiparallel β-strands. The amino-terminal domain including two cysteine residues at 21 and 98 showed considerable sequence homology with the variable domains of immunoglobulins. By a homology search using a computor program, significant homologies were found between the amino-terminal domain of P0 protein and the members of immunoglobulin superfamily including cell adhesion molecules such as the neural cell adhesion molecule and the myelin-associated glycoprotein. We concluded that P0 protein is a member of the immunoglobulin-cell adhesion molecule superfamily and may be involved in the primordial immunoglobulin domain. The amino-terminal domain of P0 protein is located on the extracellular side and may function as an adhesion molecule to form the myelin intraperiod line.