Post-translationally modified proteins make up the majority of the proteome and establish, to a large part, the impressive level of functional diversity in higher, multi-cellular organisms. Most eukaryotic post-translational protein modifications (PTMs) denote reversible, covalent additions of small chemical entities such as phosphate-, acyl-, alkyl- and glycosyl-groups onto selected subsets of modifiable amino acids. In turn, these modifications induce highly specific changes in the chemical environments of individual protein residues, which are readily detected by high-resolution NMR spectroscopy. In the following, we provide a concise compendium of NMR characteristics of the main types of eukaryotic PTMs: serine, threonine, tyrosine and histidine phosphorylation, lysine acetylation, lysine and arginine methylation, and serine, threonine O-glycosylation. We further delineate the previously uncharacterized NMR properties of lysine propionylation, butyrylation, succinylation, malonylation and crotonylation, which, altogether, define an initial reference frame for comprehensive PTM studies by high-resolution NMR spectroscopy.

Cellular oxidative stress serves as a common denominator in many neurodegenerative disorders, including Parkinson's disease. Here we use in-cell NMR spectroscopy to study the fate of the oxidation-damaged Parkinson's disease protein alpha-synuclein (α-Syn) in non-neuronal and neuronal mammalian cells. Specifically, we deliver methionine-oxidized, isotope-enriched α-Syn into cultured cells and follow intracellular protein repair by endogenous enzymes at atomic resolution. We show that N-terminal α-Syn methionines Met1 and Met5 are processed in a stepwise manner, with Met5 being exclusively repaired before Met1. By contrast, C-terminal methionines Met116 and Met127 remain oxidized and are not targeted by cellular enzymes. In turn, persisting oxidative damage in the C-terminus of α-Syn diminishes phosphorylation of Tyr125 by Fyn kinase, which ablates the necessary priming event for Ser129 modification by CK1. These results establish that oxidative stress can lead to the accumulation of chemically and functionally altered α-Syn in cells.

S129-phosphorylated alpha-synuclein (α-syn) is abundantly found in Lewy-body inclusions of Parkinson's disease patients. Residues neighboring S129 include the α-syn tyrosine phosphorylation sites Y125, Y133, and Y136. Here, we use time-resolved NMR spectroscopy to delineate atomic resolution insights into the modification behaviors of different serine and tyrosine kinases targeting these sites and show that Y125 phosphorylation constitutes a necessary priming event for the efficient modification of S129 by CK1, both in reconstituted kinase reactions and mammalian cell lysates. These results suggest that α-syn Y125 phosphorylation augments S129 modification under physiological in vivo conditions.

Aggregation of hyperphosphorylated TDP-43 is the hallmark pathological feature of the most common molecular form of frontotemporal lobar degeneration (FTLD–TDP) and in the vast majority of cases with amyotrophic lateral sclerosis (ALS–TDP). However, most of the specific phosphorylation sites remain to be determined, and their relevance regarding pathogenicity and clinical and pathological phenotypic diversity in FTLD–TDP and ALS–TDP remains to be identified. Here, we generated a novel antibody raised against TDP-43 phosphorylated at serine 375 (pTDP-43S375) located in the low-complexity domain, and used it to investigate the presence of S375 phosphorylation in a series (n = 44) of FTLD–TDP and ALS–TDP cases. Immunoblot analysis demonstrated phosphorylation of S375 to be a consistent feature of pathological TDP-43 species, including full-length and C-terminal fragments, in all FTLD–TDP subtypes examined (A–C) and in ALS–TDP. Of particular interest, however, detailed immunohistochemical analysis showed striking differences in the immunoreactivity profile of inclusions with the pTDP-43S375 antiserum among pathological subtypes. TDP-43 pathology of ALS–TDP, FTLD–TDP type B (including cases with the C9orf72 mutation), and FTLD–TDP type C all showed strong pTDP-43S375 immunoreactivity that was similar in amount and morphology to that seen with an antibody against TDP-43 phosphorylated at S409/410 used as the gold standard. In stark contrast, TDP-43 pathology in sporadic and genetic forms of FTLD–TDP type A (including cases with GRN and C9orf72 mutations) was found to be almost completely negative by pTDP-43S375 immunohistochemistry. These data suggest a subtype-specific, conformation-dependent binding of pTDP-43S375 antiserum to TDP-43 aggregates, consistent with the idea of distinct structural TDP-43 conformers (i.e., TDP-43 strains) as the molecular basis for the phenotypic diversity in TDP-43 proteinopathies.

Cell signaling is governed by dynamic changes in kinase and phosphatase activities, which are difficult to assess with discontinuous readout methods. Here, we introduce an NMR-based reporter approach to directly identify active kinases and phosphatases in complex physiological environments such as cell lysates and to measure their individual activities in a semicontinuous fashion. Multiplexed NMR profiling of reporter phosphorylation states provides unique advantages for kinase inhibitor studies and reveals reversible modulations of cellular enzyme activities under different metabolic conditions.

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