Identification of a brain-specific human cerebrospinal fluid glycoprotein, beta-trace protein

A prominent human cerebrospinal fluid (CSF) protein, P5, identified at mass 19-24 kDa and charge 5.5, by two-dimensional electrophoresis (2DE) and silver staining, has been previously demonstrated to be reduced in quantity in the CSF of patients with multiple sclerosis and schizophrenia. We report the purification and partial amino acid sequences from five tryptic fragments of P5. These sequences are not those of any known sequence in the Protein Identification Resource (PIR release 31) database. Synthetic peptides from two of the sequences were used to raise rabbit polyclonal antibodies. These antibodies detected P5 on 2DE blots of normal CSF proteins and other proteins of the same mass with a charge distribution between 5.17-8.5. These proteins comprise 5-10% of the total CSF protein and their mass, charge, abundance and predominance in CSF over plasma are consistent with a protein that had been initially characterized with antibodies, beta-trace protein. Glycosidase studies confirm that most of these proteins are due to sialic acid modifications that are N-linked to an 18 kDa protein, but other charge and mass variations also exist. 2DE blots of 26 types of human tissue and body fluid were immunostained. Of these, anti-P5 serum detected proteins of the same mass and charge as beta-trace protein only in brain samples. Proteins of different mass and charge from beta-trace protein were clearly immunostained in samples of eight tissues.(ABSTRACT TRUNCATED AT 250 WORDS)