Characterization of nucleotide pyrophosphatase-5 as an oligomannosidic glycoprotein in rat brain

Membrane glycoproteins of neural cells play crucial roles in axon guidance, synaptogenesis, and neuronal transmission. We have here characterized membrane glycoproteins containing terminal alpha-mannose residues in rat brain membranes. Affinity purification using Galanthus nivalis agglutinin, that is highly specific for terminal alpha-mannose residues, revealed a 50-kDa protein as well as 80-kDa SHPS-1 and 45-kDa beta2 subunit of Na,K-ATPase in rat brain membranes. Combination of N-terminal peptide sequencing and mass spectrometry indicated that the 50-kDa protein was rat nucleotide pyrophosphatase-5 (NPP-5). In contrast to other NPPs, NPP-5 was a type-I transmembrane protein. Northern blot analysis showed that NPP-5 was highly expressed in brain, but also expressed in other peripheral tissues. However, we could not detect either the NPP activity or the lysophospholipase D activity in the immunoprecipitates with antibodies to NPP-5 from rat brain membranes. These data, therefore, suggest that NPP-5 is a neural oligomannosidic glycoprotein that may participate in neural cell communications.