Formation of S-(carboxymethyl)-cysteine in rat liver mitochondrial proteins: effects of caloric and methionine restriction
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Maillard reaction contributes to the chemical modification and cross-linking of proteins. This process plays a significant role in the aging process and determination of animal longevity. Oxidative conditions promote the Maillard reaction. Mitochondria are the primary site of oxidants due to the reactive molecular species production. Mitochondrial proteome cysteine residues are targets of oxidative attack due to their specific chemistry and localization. Their chemical, non-enzymatic modification leads to dysfunctional proteins, which entail cellular senescence and organismal aging. Previous studies have consistently shown that caloric and methionine restrictions, nutritional interventions that increase longevity, decrease the rate of mitochondrial oxidant production and the physiological steady-state levels of markers of oxidative damage to macromolecules. In this scenario, we have detected S-(carboxymethyl)-cysteine (CMC) as a new irreversible chemical modification in mitochondrial proteins. CMC content in mitochondrial proteins significantly correlated with that of the lysine-derived analog N ε-(carboxymethyl)-lysine. The concentration of CMC is, however, one order of magnitude lower compared with CML likely due in part to the lower content of cysteine with respect to lysine of the mitochondrial proteome. CMC concentrations decreases in liver mitochondrial proteins of rats subjected to 8.5 and 25 % caloric restriction, as well as in 40 and 80 % methionine restriction. This is associated with a concomitant and significant increase in the protein content of sulfhydryl groups. Data presented here evidence that CMC, a marker of Cys-AGE formation, could be candidate as a biomarker of mitochondrial damage during aging.
KeywordsAging Carboxymethylated proteins Dietary restriction Oxidative stress Protein damage Protein cysteine content Sulfhydryl groups
This study was supported in part by I + D grants from the Spanish Ministry of Science and Innovation (BFU2008-00335/BFI and BFU2011-23888), and BSCH-UCM (2009–2010) to G.B; grant from the Spanish Ministry of Health (PI11/01532) to M.P.O; and grants from the Spanish Ministry of Science and Innovation (BFU2009-11879/BFI), and the Generalitat of Catalunya (2009SGR00735) to R.P.P. Caro and J. Gómez received predoctoral fellowships from the Ministry of Education and Science. We thank David Argiles for excellent technical assistance. The authors are grateful to the anonymous reviewers for criticisms and suggestions, which improved the manuscript. No competing financial interests exist.
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