Lysine Malonylation Is Elevated in Type 2 Diabetic Mouse Models and Enriched in Metabolic Associated Proteins

Post-translational modifications (PTMs)1 have been recognized as a common feature of proteins (1–3). More than 300 types of PTMs have been identified according to the Swiss-Prot database (4, 5). Most of them use small molecular compounds as group donors. For example, adenosine-triphosphate (ATP) is used in phosphorylation, S-adenosylmethionine (SAM) in methylation, and acetyl-CoA in acetylation. Lysine acylations including malonylation (6), succinylation (7), butyrylation (8), propionylation (9), and crotonylation (10) represent a group of PTMs that use intermediates of energy metabolism like malonyl-CoA, succinyl-CoA, butyryl-CoA, propionyl-CoA, and crotonyl-CoA as group donors. Among the lysine acylations, lysine malonylation was first identified in Escherichia coli (E. coli) and HeLa cells using a specific anti-Kmal (anti-malonyllysine) antibody (6). It was found in three proteins in E. coli and 17 proteins in HeLa cells. Using a novel chemical fluorescent probe, another group identified more than 300 malonylated protein candidates in HeLa cells (11). Despite the rapid progress in detection technologies and tools, functional studies of lysine malonylation and its role in human diseases have been lagging behind. Type 2 diabetes is characterized by hyperglycemia and production of glycated proteins. For example, glycated hemoglobin A1c (HbA1c) has been clinically used as diagnostic criteria for diabetes. In addition to glycation, the role of other types of PTMs in type 2 diabetes remains to be revealed. In fact, elevated malonyl-CoA levels have been found in type 2 diabetic patients (12), and prediabetic rats (13). And hepatic overexpression of malonyl-CoA decarboxylase (MCD) decreased malonyl-CoA and reversed insulin resistance (14). Given the use of malonyl-CoA as malonyl donor in lysine malonylation, lysine malonylation is therefore anticipated to be of functional significance in the pathogenesis of type 2 diabetes. In the present study, we observed elevated lysine malonylation in liver tissues of db/db mice after unbiased screening seven types of lysine acylations. We then detected elevated levels of lysine malonylation in liver tissues of more db/db and ob/ob mice. Using an immunoaffinity based proteomic method, we identified a total of 573 malonylated lysine sites from 268 proteins in liver tissues of wt and db/db mice. Elevation of lysine malonylation in five proteins was confirmed by immunoprecipitation coupled with Western blot analysis. Functional analysis of the malonylated proteins showed an apparent enrichment in metabolic pathways, especially those involved in the glucose and fatty acid metabolism. Our study indicates the putative association between protein lysine malonylation and type 2 diabetes.