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author:("loko, paschal")
1.  Knowledge management for systems biology a general and visually driven framework applied to translational medicine 
BMC Systems Biology  2011;5:38.
To enhance our understanding of complex biological systems like diseases we need to put all of the available data into context and use this to detect relations, pattern and rules which allow predictive hypotheses to be defined. Life science has become a data rich science with information about the behaviour of millions of entities like genes, chemical compounds, diseases, cell types and organs, which are organised in many different databases and/or spread throughout the literature. Existing knowledge such as genotype - phenotype relations or signal transduction pathways must be semantically integrated and dynamically organised into structured networks that are connected with clinical and experimental data. Different approaches to this challenge exist but so far none has proven entirely satisfactory.
To address this challenge we previously developed a generic knowledge management framework, BioXM™, which allows the dynamic, graphic generation of domain specific knowledge representation models based on specific objects and their relations supporting annotations and ontologies. Here we demonstrate the utility of BioXM for knowledge management in systems biology as part of the EU FP6 BioBridge project on translational approaches to chronic diseases. From clinical and experimental data, text-mining results and public databases we generate a chronic obstructive pulmonary disease (COPD) knowledge base and demonstrate its use by mining specific molecular networks together with integrated clinical and experimental data.
We generate the first semantically integrated COPD specific public knowledge base and find that for the integration of clinical and experimental data with pre-existing knowledge the configuration based set-up enabled by BioXM reduced implementation time and effort for the knowledge base compared to similar systems implemented as classical software development projects. The knowledgebase enables the retrieval of sub-networks including protein-protein interaction, pathway, gene - disease and gene - compound data which are used for subsequent data analysis, modelling and simulation. Pre-structured queries and reports enhance usability; establishing their use in everyday clinical settings requires further simplification with a browser based interface which is currently under development.
PMCID: PMC3060864  PMID: 21375767
2.  Components of a Ubiquitin Ligase Complex Specify Polyubiquitination and Intracellular Trafficking of the General Amino Acid Permease 
The Journal of Cell Biology  2001;153(4):649-662.
Gap1p, the general amino acid permease of Saccharomyces cerevisiae, is regulated by intracellular sorting decisions that occur in either Golgi or endosomal compartments. Depending on nitrogen source, Gap1p is transported to the plasma membrane, where it functions for amino acid uptake, or to the vacuole, where it is degraded. We found that overexpression of Bul1p or Bul2p, two nonessential components of the Rsp5p E3–ubiquitin ligase complex, causes Gap1p to be sorted to the vacuole regardless of nitrogen source. The double mutant bul1Δ bul2Δ has the inverse phenotype, causing Gap1p to be delivered to the plasma membrane more efficiently than in wild-type cells. In addition, bul1Δ bul2Δ can reverse the effect of lst4Δ, a mutation that normally prevents Gap1p from reaching the plasma membrane. Evaluation of Gap1p ubiquitination revealed a prominent polyubiquitinated species that was greatly diminished in a bul1Δ bul2Δ mutant. Both a rsp5-1 mutant and a COOH-terminal truncation of Gap1p behave as bul1Δ bul2Δ, causing constitutive delivery of Gap1p to the plasma membrane and decreasing Gap1p polyubiquitination. These results indicate that Bul1p and Bul2p, together with Rsp5p, generate a polyubiquitin signal on Gap1p that specifies its intracellular targeting to the vacuole.
PMCID: PMC2192387  PMID: 11352928
ubiquitin; Golgi; BUL1; E4; GAP1
3.  Uptake of the ATP-Binding Cassette (ABC) Transporter Ste6 into the Yeast Vacuole Is Blocked in the doa4 Mutant 
Molecular Biology of the Cell  2001;12(4):1047-1059.
Previous experiments suggested that trafficking of the a-factor transporter Ste6 of Saccharomyces cerevisiae to the yeast vacuole is regulated by ubiquitination. To define the ubiquitination-dependent step in the trafficking pathway, we examined the intracellular localization of Ste6 in the ubiquitination-deficient doa4 mutant by immunofluorescence experiments, with a Ste6-green fluorescent protein fusion protein and by sucrose density gradient fractionation. We found that Ste6 accumulated at the vacuolar membrane in the doa4 mutant and not at the cell surface. Experiments with a doa4 pep4 double mutant showed that Ste6 uptake into the lumen of the vacuole is inhibited in the doa4 mutant. The uptake defect could be suppressed by expression of additional ubiquitin, indicating that it is primarily the result of a lowered ubiquitin level (and thus of reduced ubiquitination) and not the result of a deubiquitination defect. Based on our findings, we propose that ubiquitination of Ste6 or of a trafficking factor is required for Ste6 sorting into the multivesicular bodies pathway. In addition, we obtained evidence suggesting that Ste6 recycles between an internal compartment and the plasma membrane.
PMCID: PMC32286  PMID: 11294906

Results 1-3 (3)