Aprataxin Is an AMP-Lysine Hydrolase

Abstract

Ataxia-oculomotor apraxia syndrome 1 (AOA), a neurological disorder characterized by abnormal movements of the head and eye, is associated with mutation of APTX , the gene that encodes aprataxin (a nuclear protein that mediates protein-protein interactions as part of the DNA damage response). Curiously, though, aptx -mutant cells do not show evidence of a major deficit in this response. Noting that APTX mutations associated with AOA involve either a histidine triad (HIT) domain similar to that of Hint (an AMP-lysine hydrolase) or the HIT domain's immediate C-terminal region, Seidle et al. used fluorigenic substrates to show that aprataxin acted as an AMP-lysine and GMP-lysine hydrolase. Aprataxin contains an N-terminal forkhead-associated (FHA) domain and a C-terminal zinc-finger domain, as well as the HIT domain; its AMP-lysine hydrolase activity depended on the Hint active site and also on the presence of the FHA domain, whereas the zinc-finger domain was necessary for protein stability. The authors used SDS-PAGE and Western analysis, together with analysis of biochemical activity against an adenylylated lysine substrate, to show that eight disease-associated mutations were characterized by a major loss of both protein stability and enzymatic activity. A mutation associated with less severe disease displayed a less dramatic loss of protein stability and enzymatic activity. Thus, the authors conclude that it is the loss of the ability of aprataxin to hydrolyze nucleotidylated protein modifications that is associated with the development of AOA. H. F. Seidle, P. Biegnowski, C. Brenner, Disease-associated mutations inactivate AMP-lysine hydrolase activity of aprataxin. J. Biol. Chem. 280 , 20927-20931 (2005). [Abstract] [Full Text]