Proteomics of bovine myelin sheath: Characterization of a truncated form of P0 by MALDI-TOF/TOF mass spectrometry

The glycoprotein PO, the major structural protein of the peripheral nerve myelin, plays a critical role in holding myelin lamellae together via interaction of both extracellular and cytoplasmic domains. Mutations in the human PO gene give rise to severe and progressive forms of dominantly inherited peripheral neuropathies like CMT1B. Here we report on the characterization of a bovine PO-derived protein of nearly 26 kD that corresponds to the PO protein truncated in its cytoplasmic domain. Matrix assisted laser desorption ionization (MALDI)-time-of-flight/time-of-flight (TOF/TOF) mass spectrometry (MS) analysis on its tryptic digest has provided a peptide mapping, the main difference of which from the normal PO analog was represented by the absence of the cluster of peaks at m/z 1513.7501, 1530.7701, and 1546.7651. The latter corresponds to the PO fragment QTPVLYAMLDHSR and to its pyroglutamic and methionine-oxidized derivatives. The species at 1530.7701 covering the sequence 186-198 of P0 is not an artifact and might have a functional role in the myelin architecture. RI NAPOLI, ANNA/B-5250-2011; Di Donna, Leonardo/D-5707-2011