Assesment of protein gene product (pgp9.5) enzyme activity against potential Peptide substrate.

OBJECTIVE: PGP9.5 is a human neuron specific ubiquitin carboxyl-terminal hydolase that has been shown by immunuhistochemistry to be present selectively in ubiquitinated inclusions in chronic human degenerative disease. Paraffin sections known to contain ubiquitinprotein conjugate immunureactivity in neurofibrillary tangles (NFT), cortical Lewy bodies, Rosenthal fibres and in Pick bodies were immunostained with PGP9.5. In Alzheimer's disease loosely arranged globose-type neurofibrillary tangles (NFTs) were immunostained together with neuritis surrounding senile plaques (SP). While PGP9.5 has been demonstrated to have ubiquitin carboxy-terminal ethyl esterase activity, there has not been clear identification of its substrate specificity. The main aim was, therefore, to purify PGP9.5 and study its carboxyl-terminal hydrolase activity using, as substrates, synthetic peptides that were chosen to reflect the known possible functions of the enzyme.
MATERIALS AND METHODS: Ubiquitin is cleaved from conjugates by ubiquitin carboxyl-terminal hydrolases, one of which is protein gene product 9.5 (PGP 9.5). PGP9.5 was purified to homogeneity from human post-mortem brain tissue, its identity confirmed by protein sequence determination. Potential peptide substrates were incubated with PGP 9.5 and assayed by HPLC.
RESULTS: Overlap region of ubiquitin in branched gene products were not substrates. Evidence was obtained for cleavage of linearly-conjugated polyubiquitin.
CONCLUSION: Degradation of abnormal proteins by ubiquitin system depends on binding structure of ubiquitins. It has been shown that only linear ubiquitis are substrate for the PGP 9.5. The importance of it is not well understood.