Submitochondrial distribution and delayed proteolysis of subunit c of the H+-transporting ATP-synthase in ovine ceroid-lipofuscinosis

The neuronal ceroid-lipofuscinose (NCL) are recessively inherited lysosomal storage diseases in children and animals. The major stored protein in many of these diseases is subunit c of the mitochondrial inner membrane H+-tran sporting ATP-synthase. Previous studies of naturally occurring ovine ceroid -lipofuscinosis (OCL) in South Hampshire sheep showed that the genes and tr anscripts for subunit c were normal and inferred that this protein was expr essed normally in mitochondria prior to storage in lysosomes. Accumulation in mitochondria has not been conclusively established and we have therefore used the South Hampshire model to demonstrate approximately 1.8-fold norma l levels of subunit c in mitochondrial inner membranes prepared from liver. Other mitochondrial inner membrane and ATP-synthase proteins that could be detected by mass spectrometry (MS) or two-dimensional electrophoresis (2-D E) were present in normal amounts. The accumulating subunit c showed normal post-translational modification but was abnormally resistant to proteolysi s. These results are consistent with the hypothesis that OCL may result fro m a mitochondrial disorder that affects turnover of correctly expressed sub unit c, although we cannot exclude the possibility that a postmitochondrial defect delays processing of subunit c out of mitochondria.