Year: 2011
Type: article
Abstract: Glycation and lipoxidation are two typical contributors to irreversible posttranslational modification in biological systems, which contribute to age-related diseases.In this dissertation, mechanistic studies are reported that elucidate the chemistry of glycation and lipoxodation, and their biological consequences.To understand the contribution of glycation to diabetic cataract, glycated recombinant human αA crystallin was analyzed by mass spectrometry.The data revealed that R12, R65, R103, R112, R157 and R163 were hot spots of dicarbonyl modifications.The most prevalent site for glycation was K166, which was confirmed by the fact that the mutations of K166 can drastically decrease the levels of advanced glycation end products (AGEs).The selectivities were hypothetically attributed to the catalytic effect of glutamate adjacent lysine.The major sugar-derived cross-link was observed at K166-R163, K166-R103, and K166-R117.The latter two cross-link sites suggested a transient attraction between the C-terminus and the edge of β6 and β7 in αA crystallin, which may contribute to the inter-molecular attractions between crystallins.The comparative analysis of carbonyl and oxidant stress in human lens and skin revealed that the major modifications in lens were ornithine, methylglyoxal-derived hydroimidazolone (MG-H1) and carboxymethyllysine (CML), whereas in skin were xx ornithine, FL and glucosepane.The potential explanation to these facts is that lens proteins can more efficiently use glycoxidation to prevent sugar-derived cross-links.Most AGEs accumulated with aging both in lens and skin.However, diabetes had no impact on MG-H1, glyoxal hydroimidazolone, CML and carboxylethyllysine.These observations suggested that current diabetes medication can ameliorate dicarbonyl stress, but not glycation and consequent cross-linking.The strikingly high MG-H1 level in human lens originated from the high concentration of ascorbic acid in lens.Finally, modifications derived from epoxyketooctadecenoic acids (EKODEs) were investigated.Both the reactions of EKODE I and II with buanethiol are initiated with Michael addition.The resulting adducts can be converted to epoxy ring opening products through an intra-molecular [1, 2] shift or [1, 5] shift of butylthio.The thiolysis reactions were prompted by both heat and light.Similar reactions were observed in the reactions of EKODEs with cyeteine, and the modifications of EKODEs to histidine were dominated by Michael adducts.
Author: Jianye Zhang
Institution: Case Western Reserve University
Language: English
Subfield: Clinical Biochemistry
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2599923116