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Global Chemical Modifications Comparison of Human Plasma

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Global Chemical Modifications Comparison of Human Plasma www.nature.com/scientificreports OPEN Global chemical modifcations comparison of human plasma proteome from two diferent age groups Yongtao Liu1,3, Xuanzhen Pan1,3, Mindi Zhao2 & Youhe Gao1* In this study, two groups of human plasma proteome at diferent age groups (old and young) were used to perform a comparison of global chemical modifcations, as determined by tandem mass spectrometry (MS/MS) combined with non-limiting modifcation identifcation algorithms. The sulfydryl in the cysteine A total of 4 molecular modifcations were found to have signifcant diferences passing random grouping tests: the succinylation and phosphorylation modifcation of cysteine (Cys, C) and the modifcation of lysine (Lys, K) with threonine (Thr, T) were signifcantly higher in the old group than in the young group, while the carbamylation of lysine was lower in the young group. We speculate that there is an increase in certain modifed proteins in the blood of the old people which, in turn, changes the function of those proteins. This change may be one of the reasons why old people are more likely than young people to be at risk for age-related diseases, such as metabolic diseases, cerebral and cardiovascular diseases, and cancer. Te biological processes of living things/organisms can perform and operate in mutual coordination and high- efciency cooperation simultaneously, relying on the synthesis, catalysis, and regulatory reactions in which proteins are involved. Proteins are biological macromolecule with complex structures, and the diference in the high-level structures of proteins determines their diferent biochemical activities, which can perform specifc functions through a higher-level network formed by the combination of proteins 1. Chemical modifcation of proteins refers to the covalent group reaction of amino acid residues or chain ends. In general, a few changes in chemical structure do not afect the biological activity of proteins, which are called modifcation of nonessential parts of the protein. However, in most cases, changes in molecular structure will signifcantly change the physi- cal and chemical properties of the protein, change the conformation of the protein, and make the activity of the protein vary, and then the function that it performs is changed 2. Terefore, even if there is no change in the protein content level, but some small changes in the level of chemical modifcation, the function of the proteins will change signifcantly, which means that the chemical modifcation of the proteins enriches the diferent functions of the protein in another dimension. Te efects of chemical modifcation of proteins on the functions of proteins are mainly shown in the following three aspects: (1) Even if a modifcation occurs, the functions of proteins will be afected. (2) Te same type or diferent type of modifcations of the diferent amino acids have diferent efects on the same protein’s function. (3) Te same protein may undergo many types of chemical modifcation, which makes the biological process in which it participates a more variable and complex process 3. Te main types of chemical modifcations related to proteins are as follows: (1) Post-translational modifcations (PTMs) refer to the chemical modifcation of a protein afer translation 4. Te precursor of post-translationally modifed protein ofen has no biological activity. Post-translational modifcation of a specifc modifed enzyme is usually required for it to become a functional mature protein and perform its specifc biological functions5,6. (2) Chemical-derived modifcation of proteins refers to a kind of modifcation that introduces new groups or removes original/intrinsic groups in the protein side-chain, usually including spontaneous non-enzymatic modifcations, as well as the modifcations introduced by cross-linking agents and artifcial agents. (3) Amino 1Department of Biochemistry and Molecular Biology, Beijing Key Laboratory of Gene Engineering Drug and Biotechnology, Beijing Normal University, Beijing, China. 2Department of Laboratory Medicine, National Geriatrics Center, Beijing Hospital, Beijing, China. 3These authors contributed equally: Yongtao Liu and Xuanzhen Pan. *email: [email protected] SCIENTIFIC REPORTS | (2020) 10:14998 | https://doi.org/10.1038/s41598-020-72196-z 1 Vol.:(0123456789) www.nature.com/scientificreports/ acid substitution refers to the change in protein properties and functions caused by the substitution of amino acids in the protein side-chain by other kinds of amino acids. Tese changes are the types of modifcations that signifcantly afect protein function. Mass spectrometry can not only realize the acquisition of large-scale data and in-depth mining but also achieve the accurate determination of specifc protein targeted modifcations. With the continuous development of scientifc instruments, ultrahigh-resolution and tandem mass spectrometry (MS/MS) provide more abun- dant information or data for proteomics and chemical modifcation research, which also facilitates the accurate identifcation of chemical modifcation sites in the protein chain. In the process of proteomic data analysis, it is usually necessary to search and compare the proteomic database of species, and high-resolution tandem mass spectrometry is the primary method for obtaining a large amount of protein modifcation information. When using the search engine to search the database, known types of protein chemical modifcation were usually set. Tis type of search method is called a restricted search, but it is difcult to identify a new type of modifcation with a type in the product that is unknown 7. Terefore, comprehensive and non-limiting modifcation identi- fcation plays an important role in understanding all the chemical modifcation information contained in the sample proteome. Open-pFind is an open sequence library search algorithm that integrates the UniMod database, analyses, and processes the collected mass spectrum data through an open search to obtain the global chemical modifcation information of samples 8–10. Plasma is an important part of the internal environment and homeostasis, and it plays a role in transporting the substances needed for maintaining the life activities and the wastes generated of the body. Proteins are rich in variety and content in the plasma, and the components are easily afected by metabolism, physiology, and pathol- ogy. All metabolites or wastes in cells and tissues are transported and exchanged through the blood; the study of plasma proteomics may refect the physiological state of the body at a specifc stage. Chemical modifcation levels are another important research area of plasma proteomics. A comprehensive comparison of the changes in plasma proteome chemical modifcation levels will provide multiple dimensions of information for the study of physiological changes in the body 11. At present, there are more than 1,500 kinds of chemical modifcations in the UniMod12, PSI-MOD13, and RESID databases. Tere are many kinds of chemical modifcations in the human plasma proteome, such as N-terminal acetylation, phosphorylation in the side chain, methylation, glycosylation, ubiquitination, and disulfde bonds between two chains. Te plasma proteome can refect the nuances defning the diferences between age and ageing14. A study of the proteome changes in another body fuid, urine, dem- onstrated that this fuid can be analyzed to elucidate body ageing 15. Even the common physiological process of hunger can be analyzed to characterize the urine proteome16. However, the comparison of the global proteome chemical modifcations in two kinds of body fuids (plasma and urine) showed the diferences in modifcations between diferent types of samples17. Based on the importance of chemical modifcations in the human plasma proteome, this study attempted to compare the diferences in the global chemical modifcation levels of the plasma proteome at two diferent age groups, as determined by high-resolution tandem mass spectrometry combined with non-limiting modifcation identifcation (Open-pFind). Results Identifcation of total protein by using the bottom-up proteomics technology. In the label- free proteomic analysis, 20 (10/10) samples were analyzed by LC–MS/MS. Afer retrieving data (.raw) based on pFind studio, the analysis results can be browsed and exported in pBuild studio. Te 120-min liquid chromato- gram gradient was analyzed, and 628–781 kinds of proteins (average 724) and 7,526–11,464 kinds of peptides (average 10,238) were identifed in the plasma samples without high-abundance protein removal. About the raw data of pFind, we had submitted to iProX Datasets (https ://www.iprox .org/page/HMV00 6.html) under the Project ID: IPX0002313000. And the results of pFind were showed in Supplementary Table 1. Comparison of post-translational modifcations of the plasma proteome between the young and old groups. A total of 1,169 modifcations (including low abundance modifcations, that is, each modi- fcation is identifed at least once) were identifed in the plasma samples of the old group, and 1,154 modif- cations (including low abundance modifcations) were identifed in the plasma samples of the young group. Eighty-eight percent of the modifcations are of the same type, and the remaining 12% are related (Fig. 1). Among the 163 unique protein chemical modifcations in the two groups, 158 of them had less than 50% repeatability in each group, and only 5 of them met the conditions of more than 50% reproducibility. Tey are four kinds of modifcations in the old group: Arg → Phe [R], Arg → Trp [R],
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