LYSINE METHYLATION OF MITOCHONDRIAL ATP SYNTHASE SUBUNIT-C STORED IN TISSUES OF DOGS WITH HEREDITARY CEROID-LIPOFUSCINOSIS

Certain forms of ceroid lipofuscinosis, a hereditary degenerative dise ase, are characterized by accumulation of large amounts of subunit c o f mitochondrial ATP synthase in lysosomal storage bodies of numerous t issues. The subunit c protein appears to constitute a major fraction o f the total storage body protein. In previous studies it was demonstra ted that hydrolysates of total storage body protein from affected huma ns and sheep contain significant amounts of epsilon-N-trimethyllysine (TML). This finding suggested that one or both of the two lysine resid ues of subunit c might be methylated in the stored form of the protein . The normal subunit c protein from mitochondria does not appear to be methylated. Using a putative canine model for the juvenile form of ce roid lipofuscinosis, analyses were conducted to determine whether lyso somal storage of subunit c was accompanied by lysine methylation of th is protein. In affected dogs, as in humans and sheep with hereditary c eroid lipofuscinosis, the storage bodies were found to contain large a mounts of subunit c protein, as indicated by polyacrylamide gel electr ophoresis and partial amino acid sequence analysis. The subunit c prot ein partially purified from isolated storage bodies was found to conta in lysine and TML in an almost equimolar ratio. Normal subunit c conta ins 2 lysine residues, one at position 7 and the other at position 43. Removal of the first 7 residues of the partially purifIed protein thr ough sequential Edman degradation resulted in a dramatic increase in t he TML to Lysine ratio in the residual protein. This suggests that lys ine residue 43 is methylated. Confirmation that residue 43 of the stor ed protein is TML was obtained by amino acid sequence analysis after c leavage of the protein with trypsin. This finding strongly suggests th at specific methylation of lysine residue 43 of mitochondrial ATP synt hase plays a central role in the lysosomal storage of this protein.