Roland Krause

Functional organization of the yeast proteome by systematic analysis of protein complexes

Most cellular processes are carried out by multiprotein complexes. The identification and analysis of their components provides insight into how the ensemble of expressed proteins (proteome) is organized into functional units. We used tandem-affinity purification (TAP) and mass spectrometry in a large-scale approach to characterize multiprotein complexes in Saccharomyces cerevisiae. We processed 1,739 genes, including 1,143 human orthologues of relevance to human biology, and purified 589 protein assemblies. Bioinformatic analysis of these assemblies defined 232 distinct multiprotein complexes and proposed new cellular roles for 344 proteins, including 231 proteins with no previous functional annotation. Comparison of yeast and human complexes showed that conservation across species extends from single proteins to their molecular environment. Our analysis provides an outline of the eukaryotic proteome as a network of protein complexes at a level of organization beyond binary interactions. This higher-order map contains fundamental biological information and offers the context for a more reasoned and informed approach to drug discovery.

Comparative assessment of large-scale data sets of protein–protein interactions

Comprehensive protein–protein interaction maps promise to reveal many aspects of the complex regulatory network underlying cellular function. Recently, large-scale approaches have predicted many new protein interactions in yeast. To measure their accuracy and potential as well as to identify biases, strengths and weaknesses, we compare the methods with each other and with a reference set of previously reported protein interactions.

The Human Phenotype Ontology in 2017

Deep phenotyping has been defined as the precise and comprehensive analysis of phenotypic abnormalities in which the individual components of the phenotype are observed and described. The three components of the Human Phenotype Ontology (HPO; www.human-phenotype-ontology.org) project are the phenotype vocabulary, disease-phenotype annotations and the algorithms that operate on these. These components are being used for computational deep phenotyping and precision medicine as well as integration of clinical data into translational research. The HPO is being increasingly adopted as a standard for phenotypic abnormalities by diverse groups such as international rare disease organizations, registries, clinical labs, biomedical resources, and clinical software tools and will thereby contribute toward nascent efforts at global data exchange for identifying disease etiologies. This update article reviews the progress of the HPO project since the debut Nucleic Acids Research database article in 2014, including specific areas of expansion such as common (complex) disease, new algorithms for phenotype driven genomic discovery and diagnostics, integration of cross-species mapping efforts with the Mammalian Phenotype Ontology, an improved quality control pipeline, and the addition of patient-friendly terminology.

Mutation in the Transcriptional Regulator PhoP Contributes to Avirulence of Mycobacterium tuberculosis H37Ra Strain

Attenuated strains of mycobacteria can be exploited to determine genes essential for their pathogenesis and persistence. To this goal, we sequenced the genome of H37Ra, an attenuated variant of Mycobacterium tuberculosis H37Rv strain. Comparison with H37Rv revealed three unique coding region polymorphisms. One polymorphism was located in the DNA-binding domain of the transcriptional regulator PhoP, causing the proteins diminished DNA-binding capacity. Temporal gene expression profiles showed that several genes with reduced expression in H37Ra were also repressed in an H37Rv phoP knockout strain. At later time points, genes of the dormancy regulon, typically expressed in a state of nonreplicating persistence, were upregulated in H37Ra. Complementation of H37Ra with H37Rv phoP partially restored its persistence in a murine macrophage infection model. Our approach demonstrates the feasibility of identifying minute but distinct differences between isogenic strains and illustrates the consequences of single point mutations on the survival stratagem of M. tuberculosis.

Modular decomposition of protein-protein interaction networks

We introduce an algorithmic method, termed modular decomposition, that defines the organization of protein-interaction networks as a hierarchy of nested modules. Modular decomposition derives the logical rules of how to combine proteins into the actual functional complexes by identifying groups of proteins acting as a single unit (sub-complexes) and those that can be alternatively exchanged in a set of similar complexes. The method is applied to experimental data on the pro-inflammatory tumor necrosis factor-α (TNF-α)/NFκB transcription factor pathway.

De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy.

Epileptic encephalopathies are a phenotypically and genetically heterogeneous group of severe epilepsies accompanied by intellectual disability and other neurodevelopmental features. Using next-generation sequencing, we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy (one mutation recurred three times independently). Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia. Functional studies of the two mutations associated with this phenotype showed almost complete loss of function with a dominant-negative effect. Two further individuals presented with a different and more severe epileptic encephalopathy phenotype. They carried mutations inducing a drastic gain-of-function effect leading to permanently open channels. These results establish KCNA2 as a new gene involved in human neurodevelopmental disorders through two different mechanisms, predicting either hyperexcitability or electrical silencing of KV1.2-expressing neurons.

Identification of tightly regulated groups of genes during Drosophila melanogaster embryogenesis.

Time‐series analysis of whole‐genome expression data during Drosophila melanogaster development indicates that up to 86% of its genes change their relative transcript level during embryogenesis. By applying conservative filtering criteria and requiring ‘sharp’ transcript changes, we identified 1534 maternal genes, 792 transient zygotic genes, and 1053 genes whose transcript levels increase during embryogenesis. Each of these three categories is dominated by groups of genes where all transcript levels increase and/or decrease at similar times, suggesting a common mode of regulation. For example, 34% of the transiently expressed genes fall into three groups, with increased transcript levels between 2.5–12, 11–20, and 15–20 h of development, respectively. We highlight common and distinctive functional features of these expression groups and identify a coupling between downregulation of transcript levels and targeted protein degradation. By mapping the groups to the protein network, we also predict and experimentally confirm new functional associations.

Biomarkers of postoperative delirium and cognitive dysfunction

Elderly surgical patients frequently experience postoperative delirium (POD) and the subsequent development of postoperative cognitive dysfunction (POCD). Clinical features include deterioration in cognition, disturbance in attention and reduced awareness of the environment and result in higher morbidity, mortality and greater utilization of social financial assistance. The aging Western societies can expect an increase in the incidence of POD and POCD. The underlying pathophysiological mechanisms have been studied on the molecular level albeit with unsatisfying small research efforts given their societal burden. Here, we review the known physiological and immunological changes and genetic risk factors, identify candidates for further studies and integrate the information into a draft network for exploration on a systems level. The pathogenesis of these postoperative cognitive impairments is multifactorial; application of integrated systems biology has the potential to reconstruct the underlying network of molecular mechanisms and help in the identification of prognostic and diagnostic biomarkers.

CHD2 variants are a risk factor for photosensitivity in epilepsy

Photosensitivity in epilepsy is common and has high heritability, but its genetic basis remains uncertain. Galizia et al. reveal an overrepresentation of unique variants of CHD2 — which encodes the transcriptional regulator ‘chromodomain helicase DNA-binding protein 2’ — in photosensitive epilepsies, and show that chd2 knockdown in zebrafish causes photosensitivity.

70S-scanning initiation is a novel and frequent initiation mode of ribosomal translation in bacteria

Significance Until now, two initiation modes for bacterial translation have been described: (i) the standard 30S-binding mode, where the small ribosomal subunit selects the initiation site on an mRNA with the help of three initiation factors (IFs), and (ii) the rare initiation of leaderless mRNAs, which are mRNAs carrying the initiation AUG within the first 5 nt at the 5′-end. The existence of a third “70S-scanning” mode for bacterial initiation was conjectured in past decades but has remained experimentally unproven. Here, we demonstrate the existence of a 70S-scanning mode of initiation and characterize its mechanistic features. The three initiation modes demonstrate specific patterns of requirements for IF1 and IF3. According to the standard model of bacterial translation initiation, the small ribosomal 30S subunit binds to the initiation site of an mRNA with the help of three initiation factors (IF1–IF3). Here, we describe a novel type of initiation termed “70S-scanning initiation,” where the 70S ribosome does not necessarily dissociate after translation of a cistron, but rather scans to the initiation site of the downstream cistron. We detailed the mechanism of 70S-scanning initiation by designing unique monocistronic and polycistronic mRNAs harboring translation reporters, and by reconstituting systems to characterize each distinct mode of initiation. Results show that 70S scanning is triggered by fMet-tRNA and does not require energy; the Shine–Dalgarno sequence is an essential recognition element of the initiation site. IF1 and IF3 requirements for the various initiation modes were assessed by the formation of productive initiation complexes leading to synthesis of active proteins. IF3 is essential and IF1 is highly stimulating for the 70S-scanning mode. The task of IF1 appears to be the prevention of untimely interference by ternary aminoacyl (aa)-tRNA•elongation factor thermo unstable (EF-Tu)•GTP complexes. Evidence indicates that at least 50% of bacterial initiation events use the 70S-scanning mode, underscoring the relative importance of this translation initiation mechanism.