The relevance of the storage of subunit c of ATP synthase in different forms and models of Batten disease (NCLs)

The discoveries of specific protein storage in the NCLs, particularly of subunit c of ATP synthase in most, and the sphingolipid activator proteins, SAPs or saposins A and D in CLN1, CLN10 and an unassigned form are reviewed. The subunit c stored in the relevant NCLs is the complete mature molecule including an unusual modification found only in animal species, trimethylation of its lysine-43. Because of its strongly hydrophobic and lipid-like properties subunit c is easily overlooked or incorrectly described. This is becoming more of a problem as subunit c is not detected in standard proteomic investigations. Methods are reviewed that allow its unequivocal characterisation. Subunit c storage and cellular storage body accumulation do not cause the neuropathology characteristic of these diseases. The function of the trimethyl group on lysine-43 of subunit c is considered, along with some indications of where its normal turnover may be disrupted in the NCLs. (C) 2015 Elsevier B.V. All rights reserved.