Localization of peptidylarginine deiminase type II in a stage-specific immature oligodendrocyte from rat cerebral hemisphere.

Myelin basic protein (MBP) is composed of multiple charged isomers as the products of various posttranslational modifications. The least cationic component contains six citrulline residues converted from arginine residues by peptidylarginine deiminase (PAD). The modified MBP differs markedly from unmodified MBP in the ability to aggregate acidic lipid vesicles. However, the localization of PAD in brain has remained rather elusive. We performed Western blotting and immunocytochemical analyses of PAD type II and found that it was present in stage-specific immature oligodendrocytes but not in either type-1 astrocytes or neurons. We also confirmed that only the oligodendrocyte homogenate contained the PAD activity utilizing a sensitive method to detect citrulline-containing proteins. These data suggest that PAD type II localized in oligodendrocytes is responsible for deiminating MBP.