Jenny Ottosson

A Human Protein Atlas for Normal and Cancer Tissues Based on Antibody Proteomics

Antibody-based proteomics provides a powerful approach for the functional study of the human proteome involving the systematic generation of protein-specific affinity reagents. We used this strategy to construct a comprehensive, antibody-based protein atlas for expression and localization profiles in 48 normal human tissues and 20 different cancers. Here we report a new publicly available database containing, in the first version, ∼400,000 high resolution images corresponding to more than 700 antibodies toward human proteins. Each image has been annotated by a certified pathologist to provide a knowledge base for functional studies and to allow queries about protein profiles in normal and disease tissues. Our results suggest it should be possible to extend this analysis to the majority of all human proteins thus providing a valuable tool for medical and biological research.

A Genecentric Human Protein Atlas for Expression Profiles Based on Antibodies

An attractive path forward in proteomics is to experimentally annotate the human protein complement of the genome in a genecentric manner. Using antibodies, it might be possible to design protein-specific probes for a representative protein from every protein-coding gene and to subsequently use the antibodies for systematical analysis of cellular distribution and subcellular localization of proteins in normal and disease tissues. A new version (4.0) of the Human Protein Atlas has been developed in a genecentric manner with the inclusion of all human genes and splice variants predicted from genome efforts together with a visualization of each protein with characteristics such as predicted membrane regions, signal peptide, and protein domains and new plots showing the uniqueness (sequence similarity) of every fraction of each protein toward all other human proteins. The new version is based on tissue profiles generated from 6120 antibodies with more than five million immunohistochemistry-based images covering 5067 human genes, corresponding to ∼25% of the human genome. Version 4.0 includes a putative list of members in various protein classes, both functional classes, such as kinases, transcription factors, G-protein-coupled receptors, etc., and project-related classes, such as candidate genes for cancer or cardiovascular diseases. The exact antigen sequence for the internally generated antibodies has also been released together with a visualization of the application-specific validation performed for each antibody, including a protein array assay, Western blot analysis, immunohistochemistry, and, for a large fraction, immunofluorescence-based confocal microscopy. New search functionalities have been added to allow complex queries regarding protein expression profiles, protein classes, and chromosome location. The new version of the protein atlas thus is a resource for many areas of biomedical research, including protein science and biomarker discovery.

A global view of protein expression in human cells, tissues, and organs

Defining the protein profiles of tissues and organs is critical to understanding the unique characteristics of the various cell types in the human body. In this study, we report on an anatomically comprehensive analysis of 4842 protein profiles in 48 human tissues and 45 human cell lines. A detailed analysis of over 2 million manually annotated, high‐resolution, immunohistochemistry‐based images showed a high fraction (>65%) of expressed proteins in most cells and tissues, with very few proteins (<2%) detected in any single cell type. Similarly, confocal microscopy in three human cell lines detected expression of more than 70% of the analyzed proteins. Despite this ubiquitous expression, hierarchical clustering analysis, based on global protein expression patterns, shows that the analyzed cells can be still subdivided into groups according to the current concepts of histology and cellular differentiation. This study suggests that tissue specificity is achieved by precise regulation of protein levels in space and time, and that different tissues in the body acquire their unique characteristics by controlling not which proteins are expressed but how much of each is produced.

Size as a parameter for solvent effects on Candida antarctica lipase B enantioselectivity

Changes in solvent type were shown to yield significant improvement of enzyme enantioselectivity. The resolution of 3-methyl-2-butanol catalyzed by Candida antarctica lipase B, CALB, was studied in eight liquid organic solvents and supercritical carbon dioxide, SCCO(2). Studies of the temperature dependence of the enantiomeric ratio allowed determination of the enthalpic (Delta(R-S)Delta H(++)) as well as the entropic (Delta(R-S)Delta S(++)) contribution to the overall enantioselectivity (Delta(R-S)Delta G(++)= -RTlnE). A correlation of the enantiomeric ratio, E, to the van der Waals volume of the solvent molecules was observed and suggested as one of the parameters that govern solvent effects on enzyme catalysis. An enthalpy-entropy compensation relationship was indicated between the studied liquid solvents. The enzymatic mechanism must be of a somewhat different nature in SCCO(2), as this reaction in this medium did not follow the enthalpy-entropy compensation relation.

Rational design of enantioselective enzymes requires considerations of entropy

Entropy was shown to play an equally important role as enthalpy for how enantioselectivity changes when redesigning an enzyme. By studying the temperature dependence of the enantiomeric ratio E of an enantioselective enzyme, its differential activation enthalpy (ΔR‐SΔH‡) and entropy (ΔR‐SΔS‡) components can be determined. This was done for the resolution of 3‐methyl‐2‐butanol catalyzed by Candida antarctica lipase B and five variants with one or two point mutations. ΔR‐SΔS‡ was in all cases equally significant as ΔR‐SΔH‡ to E. One variant, T103G, displayed an increase in E, the others a decrease. The altered enantioselectivities of the variants were all related to simultaneous changes in ΔR‐SΔH‡ and ΔR‐SΔS‡. Although the changes in ΔR‐SΔH‡ and ΔR‐SΔS‡ were of a compensatory nature the compensation was not perfect, thereby allowing modifications of E. Both the W104H and the T103G variants displayed larger ΔR‐SΔH‡ than wild type but exhibited a decrease or increase, respectively, in E due to their different relative increase in ΔR‐SΔS‡.

Substrate entropy in enzyme enantioselectivity: An experimental and molecular modeling study of a lipase

The temperature dependence of the enantioselectivity of Candida antarctica lipase B for 3‐hexanol, 2‐butanol, 3‐methyl‐2‐butanol, 3,3‐dimethyl‐2‐butanol, and 1‐bromo‐2‐butanol revealed that the differential activation entropy, ΔR−SΔS‡, was as significant as the differential activation enthalpy, ΔR−SΔH‡, to the enantiomeric ratio, E. 1‐Bromo‐2‐butanol, with isosteric substituents, displayed the largest ΔR−SΔS‡. 3‐Hexanol displayed, contrary to other sec‐alcohols, a positive ΔR−SΔS‡. In other words, for 3‐hexanol the preferred R‐enantiomer is not only favored by enthalpy but also by entropy. Molecular dynamics (MD) simulations and systematic search calculations of the substrate accessible volume within the active site revealed that the (R)‐3‐hexanol transition state (TS) accessed a larger volume within the active site than the (S)‐3‐hexanol TS. This correlates well with the higher TS entropy of (R)‐3‐hexanol. In addition, this enantiomer did also yield a higher number of allowed conformations, N, from the systematic search routines, than did the S‐enantiomer. The substrate accessible volume was greater for the enantiomer preferred by entropy also for 2‐butanol. For 3,3‐dimethyl‐2‐butanol, however, neither MD‐simulations nor systematic search calculations yielded substrate accessible volumes that correlate to TS entropy. Ambiguous results were achieved for 3‐methyl‐2‐butanol.

Influence of acyl chain length on the enantioselectivity of Candida antarctica lipase B and its thermodynamic components in kinetic resolution of sec-alcohols

Abstract The enantioselectivity, E, of Candida antarctica lipase B (CALB) was found to be strongly influenced by the chain length of the achiral acyl donor employed in the transesterification of 3-methyl-2-butanol. Of the four studied acyl donors, the longest, vinyl octanoate, afforded the highest enantioselectivity. This was true over the temperature range studied, 6–70°C. Measurements of the temperature dependence of E allows for separation of the enthalpic and entropic components of enantioselectivity. Changes in E with chain length were mainly caused by changes in the entropic component except for the reaction with vinyl propionate, which differed from the others also in the enthalpic component. Optimisation of acyl donor adds one more possibility to improve the yield of enantiopurity in the production of optically active compounds apart from optimisation of solvent, temperature, water activity, and choice of enzyme.

Increased levels of recombinant human proteins with the Escherichia coli strain Rosetta(DE3).

The effect of two Escherichiacoli expression strains on the production of recombinant human protein fragments was evaluated. High-throughput protein production projects, such as the Swedish Human Protein Atlas project, are dependent on high protein yield and purity. By changing strain from E. coli BL21(DE3) to E. coli Rosetta(DE3) the overall success rate of the protein production has increased dramatically. The Rosetta(DE3) strain compensates for a number of rare codons. Here, we describe how the protein expression of human gene fragments in E. coli strains BL21(DE3) and Rosetta(DE3) was evaluated in two stages. Initially a test set of 68 recombinant proteins that previously had been expressed in BL21(DE3) was retransformed and expressed in Rosetta(DE3). The test set generated very positive results with an improved expression yield and a significantly better purity of the protein product which prompted us to implement the Rosetta(DE3) strain in the high-throughput protein production. Except for analysis of protein yield and purity the sequences were also analyzed regarding number of rare codons and rare codon clusters. The content of rare codons showed to have a significant effect on the protein purity. Based on the results of this study the atlas project permanently changed expression strain to Rosetta(DE3).

The Temperature Dependence of Enzymatic Kinetic Resolutions Reveals the Relative Contribution of Enthalpy and Entropy to Enzymatic Enantioselectivity

The temperature dependence of the enantioselectivity of several lipase-calalyzed hydrolysis and acylation reactions of racemic esters and alcohols has been determined. From the results we estimated ...

Enhancing the protein production levels in Escherichia coli with a strong promoter

In biotechnology, the use of Escherichia coli for recombinant protein production has a long tradition, although the optimal production conditions for certain proteins are still not evident. The most favorable conditions for protein production vary with the gene product. Temperature and induction conditions represent parameters that affect total protein production, as well as the amount of soluble protein. Furthermore, the choice of promoter and bacterial strain will have large effects on the production of the target protein. In the present study, the effects of three different promoters (T7, trc and lacUV5) on E. coli production of target proteins with different characteristics are presented. The total amount of target protein as well as the amount of soluble protein were analyzed, demonstrating the benefits of using a strong promoter such as T7. To understand the underlying causes, transcription levels have been correlated with the total amount of target protein and protein solubility in vitro has been correlated with the amount of soluble protein that is produced. In addition, the effects of two different E. coli strains, BL21(DE3) and Rosetta(DE3), on the expression pattern were analyzed. It is concluded that the regulation of protein production is a combination of the transcription and translation efficiencies. Other important parameters include the nucleotide‐sequence itself and the solubility of the target protein.