Post-translational Modifications in Apicomplexan Parasites

Redox-active cysteine, a highly reactive sulfhydryl, is one of the major targets of ROS. Formation of disulfide bonds and other oxidative derivatives of cysteine including sulfenic, sulfinic, and sulfonic acids, regulates the biological function of various proteins. We identified novel low-abundant cysteine modifications in cellular GAPDH purified on 2-dimensional gel electrophoresis (2D-PAGE) by employing selectively excluded mass screening analysis for nano ultraperformance liquid chromatography-electrospray-quadrupole-time of flight tandem mass spectrometry, in conjunction with MODi and MODmap algorithm. We observed unexpected mass shifts (Δm=-16, -34, +64, +87, and +103 Da) at redox-active cysteine residue in cellular GAPDH purified on 2D-PAGE, in oxidized NDP kinase A, peroxiredoxin 6, and in various mitochondrial proteins. Mass differences of -16, -34, and +64 Da are presumed to reflect the conversion of cysteine to serine, dehydroalanine (DHA), and Cys-SO2-SH respectively. To determine the plausible pathways to the formation of these products, we prepared model compounds and examined the hydrolysis and hydration of thiosulfonate (Cys-S-SO2-Cys) either to DHA (Δm=-34 Da) or serine along with Cys-SO2-SH (Δm=+64 Da). We also detected acrylamide adducts of sulfenic and sulfinic acids (+87 and +103 Da). These findings suggest that oxidations take place at redox-active cysteine residues in cellular proteins, with the formation of thiosulfonate, Cys-SO2-SH, and DHA, and conversion of cysteine to serine, in addition to sulfenic, sulfinic and sulfonic acids of reactive cysteine.

Post-translational protein modifications can be recognized by B and T lymphocytes and can potentially make "self"-proteins appear foreign to the immune system. Such modifications may directly affect major histocompatibility complex-restricted T cell recognition of processed peptides or may perturb the processing events that generate such peptides. Using the tetanus toxin C fragment protein as a test case, we show that spontaneous deamidation of asparagine residues interferes with processing by the enzyme asparagine endopeptidase (AEP) and contributes to diminished antigen presentation. Deamidation inhibits AEP action either directly, when asparagine residues targeted by AEP are modified, or indirectly, when adjacent Asn residues are deamidated. Thus, deamidation of long-lived self-proteins may qualitatively or quantitatively affect the spectrum of self-peptides displayed to T cells and may thereby contribute to the onset or exacerbation of autoimmune disease.

The increasing dynamic functions of post-translational modifications (PTMs) within protein molecules present outstanding challenges for plant biology even at this present day. Protein PTMs are among the first and fastest plant responses to changes in the environment, indicating that the mechanisms and dynamics of PTMs are an essential area of plant biology. Besides being key players in signaling, PTMs play vital roles in gene expression, gene, and protein localization, protein stability and interactions, as well as enzyme kinetics. In this review, we take a broader but concise approach to capture the current state of events in the field of plant PTMs. We discuss protein modifications including citrullination, glycosylation, phosphorylation, oxidation and disulfide bridges, N-terminal, SUMOylation, and ubiquitination. Further, we outline the complexity of studying PTMs in relation to compartmentalization and function. We conclude by challenging the proteomics community to engage in holistic approaches towards identification and characterizing multiple PTMs on the same protein, their interaction, and mechanism of regulation to bring a deeper understanding of protein function and regulation in plants.

The use of multiple ion chromatograms in on-line HPLC-MS for the characterization of post-translational and chemical modifications of proteins

A symposium at the FASEB meeting in Las Vegas in May 1988 will be devoted to the role of cofactors (vitamins, coenzymes, prosthetic groups) in and as posttranslational protein modifications; the symposium is part of a thematic focus on metabolic regulation. In planning the symposium, we decided to consider metabolic regulation in its broadest context, which should include both the short-term activity modulations in the life of contemporary organisms and the adaptations of special molecular strategies over evolutionary time. We further decided to focus the symposium context on the involvement of cofactors both as catalytic participants in and as substrates or end products of posttranslational modifications. As a preview of the actual symposium, the present discussion is an attempt to enumerate cases of cofactor involvement in these different categories: 1) essential nutrients as participants in posttranslational modifications; 2) cofactors as donor substrates in reversible, regulatory modifications; and 3) cofactor incorporation or generation as covalent constituents of proteins. The actual symposium topics are taken from category 1: vitamin C and protein hydroxylation (K. I. Karivikkio) and vitamin K and protein carboxylation (J. W. Suttie) and category 3: biotinylation (H. G. Wood), phycobiliproteins (A. Glazer), and pyruvoyl enzymes (W. Dowhan).

The identification of post-translational modifications (PTMs) in proteins has been of particular interest in the elucidation of human diseases and the improvement of therapeutic proteins. Herein, we report a novel strategy toward the construction of fingerprint-based PTM-sensing systems as an alternative to conventional specific recognition tools. Our strategy is based on poly-l-lysine (PLL) derivatives with two distinct properties suitable to fingerprint-based protein-sensing: (i) a turn-on fluorescent signal upon binding to proteins and (ii) condition-dependent cross-reactivity toward proteins and PTMs. One type of PLL derivative under varying solution properties (pH value and ionic strength) was sufficient to construct a sensing array that produces unique fluorescence fingerprints for structurally similar mammalian albumins with/without a wide variety of chemical modifications corresponding to PTMs. This approach was also applicable for the recognition of deviations in physicochemical properties of proteins as a result of realistic glycation and phosphorylation events. Multivariate analyses of the thus obtained fingerprints successfully identified analytes with 100% accuracy (qualitatively and quantitatively) in all cases. This study thus demonstrates for the first time a fingerprint-based sensing of proteins with/without PTMs using a single, highly accessible, and tunable synthetic polymer, and accordingly offers a powerful platform for simple high-throughput sensing of PTMs in proteins.

提出了地震微观前兆预报网络系统设计的一整套详细方案，包括地震模型、基岩传感器网络和数据融合、信号处理技术和网络系统设计。本文介绍网络系统设计方案，包括光纤传感器在地震预报网络中的应用、传感器网络平台的选择和网络设计、地震源定位的相干声阵列处理技术、光数据通信技术。

Chapter 1 - Posttranslational Modifications of Proteins and Their Role in Biological Processes and Associated Diseases

Post-translational modification (PTM) of proteins regulates cellular proteostasis by expanding protein functional diversity. This naturally leads to increased proteome complexity as a result of PTM crosstalk. Here, we used the molecular chaperone protein, Heat shock protein-90 (Hsp90), which is subject to a plethora of PTMs, to investigate this concept. Hsp90 is at the hub of proteostasis and cellular signaling networks in cancer and is, therefore, an attractive therapeutic target in cancer. We demonstrated that deletion of histone deacetylase 3 (HDAC3) and histone deacetylase 8 (HDAC8) in human cells led to increased binding of Hsp90 to both ATP and its ATP-competitive inhibitor, Ganetespib. When bound to this inhibitor, Hsp90 from both HDAC3 and HDAC8 knock-out human cells exhibited similar PTMs, mainly phosphorylation and acetylation, and created a common proteomic network signature. We used both a deep-learning artificial intelligence (AI) prediction model and data based on mass spectrometry analysis of Hsp90 isolated from the mammalian cells bound to its drugs to decipher PTM crosstalk. The alignment of data from both methods demonstrates that the deep-learning prediction model offers a highly efficient and rapid approach for deciphering PTM crosstalk on complex proteins such as Hsp90.

Chromatin modifications, epigenetics, and how protozoan parasites regulate their lives

Mass Spectrometry (MS) has revolutionized the way we study biomolecules, especially proteins, their interactions and posttranslational modifications (PTM). As such MS has established itself as the leading tool for the analysis of PTMs mainly because this approach is highly sensitive, amenable to high throughput and is capable of assigning PTMs to specific sites in the amino acid sequence of proteins and peptides. Along with the advances in MS methodology there have been improvements in biochemical, genetic and cell biological approaches to mapping the interactome which are discussed with consideration for both the practical and technical considerations of these techniques. The interactome of a species is generally understood to represent the sum of all potential protein-protein interactions. There are still a number of barriers to the elucidation of the human interactome or any other species as physical contact between protein pairs that occur by selective molecular docking in a particular spatiotemporal biological context are not easily captured and measured.PTMs massively increase the complexity of organismal proteomes and play a role in almost all aspects of cell biology, allowing for fine-tuning of protein structure, function and localization. There are an estimated 300 PTMS with a predicted 5% of the eukaryotic genome coding for enzymes involved in protein modification, however we have not yet been able to reliably map PTM proteomes due to limitations in sample preparation, analytical techniques, data analysis, and the substoichiometric and transient nature of some PTMs. Improvements in proteomic and mass spectrometry methods, as well as sample preparation, have been exploited in a large number of proteome-wide surveys of PTMs in many different organisms. Here we focus on previously published global PTM proteome studies in the Apicomplexan parasites T. gondii and P. falciparum which offer numerous insights into the abundance and function of each of the studied PTM in the Apicomplexa. Integration of these datasets provide a more complete picture of the relative importance of PTM and crosstalk between them and how together PTM globally change the cellular biology of the Apicomplexan protozoa. A multitude of techniques used to investigate PTMs, mostly techniques in MS-based proteomics, are discussed for their ability to uncover relevant biological function.

Emerging trends in protein post-translational modifications of lysine associated with plant stress and development.

This study investigated the dynamics of ubiquitinated proteins after the inflammatory stimulation of RAW 264.7 macrophage-like cells with bacterial lipopolysaccharide. Ubiquitination is a common protein post-translational modification that regulates many key cellular functions. We demonstrated that levels of global ubiquitination and K48 and K63 polyubiquitin chains change after lipopolysaccharide stimulation. Quantitative proteomic analysis identified 1199 ubiquitinated proteins, 78 of which exhibited significant changes in ubiquitination levels following stimulation. Integrating the ubiquitinome data with global proteomic and transcriptomic results allowed us to identify a subset of 88 proteins that were targeted for degradation after lipopolysaccharide stimulation. Using cellular assays and Western blot analyses, we biochemically validated DBC1 (a histone deacetylase inhibitor) as a degradation substrate that is targeted via an orchestrated mechanism utilizing caspases and the proteasome. The degradation of DBC1 releases histone deacetylase activity, linking lipopolysaccharide activation to chromatin remodeling in caspase- and proteasome-mediated signaling.

Cellular phenotype and function is determined by the cellular proteome. Within the cellular proteome there are processes that have a potential to significantly alter the composition of the proteome. One such process is called alternative splicing. Splicing is the removal of introns from a pre-mRNA sequence and the remaining pre-mRNA sequences, called exons, are combined. Alternative splicing modifies the intron-exon combination, and can form novel products from the different arrangement of the coding sequences. This process, due to the high potential for new, possibly unwanted products, is highly regulated and can occur in a tissue and developmental-specific fashion. The misreguation of alternative splicing has been documented in many human diseases. The regulation of alternative splicing involves a complex network of proteins and RNA. Serine-arginine repeat (SR) proteins are a known family of regulatory proteins that bind within exons to promote exon inclusion into the mature mRNA transcript. SR protein activity is regulated by the post-translational modification, phosphorylation. Another post-translational modification of SR proteins known as acetylation has recently been identified. The acetylation of lysine residues on proteins can result in changes in localization, function, and/or structure of modified proteins. The location and function of this post-translational modification on SR proteins has not been determined. Cellular acetylation status of the HepG2 cell line was increased by histone deacetylase (HDAC) inhibition, using the HDAC inhibitors MS-275 and SAHA. RNA from treated cells was isolated for use with RT-PCR arrays developed by Peter Stoilov. Western blotting was used to determine efficacy of HDAC inhibitors on total cellular acetylation. The future goal is to understand how acetylation affects alternative splicing and characterize a new post-translational modification of SR proteins.

The apicomplexan parasite Toxoplasma gondii recognizes, binds, and penetrates virtually any kind of mammalian cell using a repertoire of proteins released from late secretory organelles and a unique form of gliding motility (also named glideosome) that critically depends on actin filaments and myosin. How T. gondii glycosylated proteins mediate host-parasite interactions remains elusive. To date, only limited evidence is available concerning N-glycosylation in apicomplexans. Here we report comprehensive proteomics and glycomics analyses showing that several key components required for host cell-T. gondii interactions are N-glycosylated. Detailed structural characterization confirmed that N-glycans from T. gondii total protein extracts consist of oligomannosidic (Man(5-8)(GlcNAc)2) and paucimannosidic (Man(3-4)(GlcNAc)2) sugars, which are rarely present on mature eukaryotic glycoproteins. In situ fluorescence using concanavalin A and Pisum sativum agglutinin predominantly stained the entire parasite body. Visualization of Toxoplasma glycoproteins purified by affinity chromatography followed by detailed proteomics and glycan analyses identified components involved in gliding motility, moving junction, and other additional functions implicated in intracellular development. Importantly tunicamycin-treated parasites were considerably reduced in motility, host cell invasion, and growth. Collectively these results indicate that N-glycosylation probably participates in modifying key proteins that are essential for host cell invasion by T. gondii.