Project description:The ubiquitous redox coenzyme nicotinamide adenine dinucleotide (NAD) acts as a non-canonical cap structure on prokaryotic and eukaryotic ribonucleic acids. Here we find that in budding yeast, NAD-RNAs are abundant (>1400 species), short (<170 nt), and mostly correspond to mRNA 5'-ends. The modification percentage is low (<5%). NAD is incorporated during the initiation step by RNA polymerase II, which uses distinct promoters with a YAAG motif for this purpose. Most NAD-RNAs are 3'-truncated. At least three decapping enzymes, Rai1, Dxo1, and Npy1, guard against NAD-RNA at different cellular locations, targeting overlapping transcript populations. NAD-mRNAs do not support translation in vitro. Our work indicates that in budding yeast, most of the NAD incorporation into RNA seems to be accidental and undesirable to the cell, which has evolved a diverse surveillance machinery to prematurely terminate, decap and reject NAD-RNAs.
Project description:A progressive loss of protein homeostasis is characteristic of aging and a driver of neurodegeneration. To investigate this process quantitatively, we characterized proteome dynamics during brain aging in the short-lived vertebrate Nothobranchius furzeri combining transcriptomics and proteomics. We detected a progressive reduction in the correlation between protein and mRNA mainly due to post-transcriptional mechanisms that account for over 40% of the age-regulated proteins. These changes cause a progressive loss of stoichiometry in several protein complexes, including ribosomes, which show impaired assembly and are enriched in protein aggregates in old brains. Mechanistically, we show that reduction of proteasome activity is an early event during brain aging and is sufficient to induce proteomic signatures of aging and loss of stoichiometry in vivo. Using longitudinal transcriptomic data, we show that the magnitude of early life decline in proteasome levels is the major risk factor for mortality. Our work defines causative events in the aging process that can be targeted to prevent loss of protein homeostasis and delay the onset of age-related neurodegeneration.
Project description:Mass spectrometry-based whole proteome analysis of parental and RFX7 knock-out U2OS cells treated with 10 µM Nutlin-3a or DMSO solvent control. Ten biological replicates were used.
Project description:Reveal a specific set of proteins important to maintain centromere integrity, through quantitative PICh (Proteomics of Isolated Chromatin). Centromeric chromatin was pulled down through RNA probes annealing specifically to a 300bp-long conserved centromeric sequence.
Project description:Many proteins undergo glycosylation in the endoplasmic reticulum (ER) and the Golgi apparatus. Altered glycosylation can manifest in serious, sometimes fatal malfunctions. We recently showed that mutations in the cytoplasmic protein GDP-mannose pyrophosphorylase A (GMPPA) cause a syndrome characterized by alacrima, achalasia, mental retardation and myopathic alterations. GMPPA acts as feedback inhibitor of GDP-mannose pyrophosphorylase B (GMPPB), which provides GDP-mannose as a substrate for protein glycosylation. Loss of GMPPA enhances incorporation of mannose into glycochains of various proteins, including α-dystroglycan (α-DG), a protein that links the extracellular matrix with the cytoskeleton. Here, we show that loss of GMPPA affects the functionality of the Golgi apparatus using different approaches. First, we show a fragmentation of the Golgi apparatus in skeletal muscle fibers and in neurons of GMPPA KO mice. A major reorganization is also evident by mass spectrometry of KO tissues with a regulation of several ER- and Golgi-resident proteins. We further show that loss of GMPPA increases the retention of α-DG in the ER. Notably, mannose supplementation can mimic changes in ER and Golgi structure and function in WT cells. In summary, our data underline the importance of a balanced mannose homeostasis for structure and function of the secretory pathway.
Project description:Apicomplexan parasites use Ca2+-regulated exocytosis to secrete essential virulence factors from specialized organelles called micronemes. Ca2+-dependent protein kinases (CDPKs) are required for microneme exocytosis; however, the molecular events that regulate trafficking and fusion of micronemes with the plasma membrane remain unresolved. Here, we combine sub-minute resolution phosphoproteomics and bio-orthogonal labeling of kinase substrates in Toxoplasma gondii to identify 163 proteins phosphorylated in a CDPK1-dependent manner. In addition to known regulators of secretion, we identify uncharacterized targets with predicted functions across signaling, gene expression, trafficking, metabolism, and ion homeostasis. One of the CDPK1 targets is a putative HOOK activating adaptor. In other eukaryotes, HOOK homologs form the FHF complex with FTS and FHIP to activate dynein-mediated trafficking of endosomes along microtubules. We show the FHF complex is partially conserved in T. gondii, consisting of HOOK, an FTS homolog, and two parasite-specific proteins (TGGT1_306920 and TGGT1_316650). CDPK1 kinase activity and HOOK are required for the rapid apical trafficking of micronemes as parasites initiate motility. Moreover, parasites lacking HOOK or FTS display impaired microneme protein secretion, leading to a block in the invasion of host cells. Taken together, our work provides a comprehensive catalog of CDPK1 targets and reveals how vesicular trafficking has been tuned to support a parasitic lifestyle.
Project description:Proteome analysis by data-independent acquisition (DIA) has become a powerful approach to obtain deep proteome coverage, and has gained recent traction for label-free analysis of single cells. However, optimal experimental design for DIA-based single-cell proteomics has not been fully explored, and performance metrics of subsequent data analysis tools remain to be evaluated. Therefore, we here present DIA-ME, a data analysis strategy that exploits the co-analysis of low-input samples with a so-called matching enhancer (ME) of higher input, to increase sensitivity, proteome coverage, and data completeness. We evaluate the matching specificity of DIA-ME by a two-proteome model, and demonstrate that false discovery and false transfers are maintained at low levels when using DIA-NN software, while preserving quantification accuracy. We apply DIA-ME to investigate the proteome response of U-2 OS cells to interferon gamma (IFN-γ) in single cells, and recapitulate the time-resolved induction of IFN-γ response proteins as observed in bulk material. Moreover, we observe co- and anti-correlating patterns of protein expression within the same cell, indicating mutually exclusive protein modules and the co-existence of different cell states. Collectively our data show that DIA-ME is a powerful, scalable, and easy-to-implement strategy for single-cell proteomics.
Project description:The small nucleotide ppGpp is a conserved regulatory molecule in prokaryotes that tunes growth rate in response to nutrient availability. How ppGpp regulates growth remains poorly defined. In Escherichia coli, ppGpp directly binds RNA polymerase to modulate transcription, but it likely has other targets. Here, we develop a capture-compound mass spectrometry approach to identify more than 50 putative ppGpp targets that control many key cellular processes, including translation, polyamine synthesis, and nucleotide metabolism. We validate several proteins as bona fide ppGpp targets in vivo. In particular, we demonstrate that ppGpp inhibits the enzymes Gsk and PurF to block purine salvage and de novo synthesis, respectively. Our results indicate that downregulating ATP and GTP synthesis is a critical facet of growth control by ppGpp. Collectively, our results provide new insight into ppGpp-based growth control in E. coli and candidates for future exploration. The capture compounds developed will also enable identification of ppGpp targets in other species, including many pathogens.