Subunit c is part of the mitochondrial ATPase enzyme, the enzyme that synthesize

Question

Subunit c is part of the mitochondrial ATPase enzyme, the enzyme that synthesizes ATP from ADP in imping that occurs during electron transport. Subunit c is a small (75-amino e ATPase formed from subunits y, 8, and acid) hydrophobic protein associated with the central stalk of tl e. Subunit c forms is a transmembrane protein that forms oligomeric rings in the membrane domain of the mitochondrial ATPase. Its sequence is highly conserved among mammals. Subunit c has been found in high concentrations in lysosomes, the organelle responsible for the degradation of all cellular macromolecules. Accumulation of a specific molecule in the lysosome may indicate that the lysosomal hydrolase responsible for the breakdown of that molecule is missing or nonfunctional. Alternatively, the defect may lie in the molecule itself, a modification of the target molecule may render it resistant to lysosomal hydrolysis. In either case, failure to break down the macromolecule results in its accumulation in the lysosomes, and for reasons that are not completely understood, accumulation of even one type of molecule in the lysosomes leads to neurodegenerative disease. Accumulation of subunit c has been found in one such neurodegenerative disease, Batten disease. Subunit c from lysosomal storage bodies has been isolated and been found to be modified at lysine 43. Modification of this lysine was thought to be responsible for the disease. Recently, research scientists in Cambridge and New Zealand isolated subunit c from bovine heart mitochondria and found that the same lysine 43 modification was present in the normal bovine ATPase enzyme as in the subunit c from lysosomal storage bodies from individuals with Batten disease. We examine their results in this case study. The researches concluded that this modification is completely normal and is not responsible for causing Batten disease. The specific function of this lysine modification is unknown at this time

Explanation / Answer

Ans. The modification of lysine 43 occurs post translationally. In this modification the associated amino acid lies in the polar loop region and links the two transmembrane alpha helices of the protein. The additional mass of about 42 arises due to the trimethylation at the N terminal of the amino acid. The function of the trimethylysine derivative would be obscure in the ATP synthase complex. The trimethylated residue provides site for cardiolipin binding.

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