Selective protein degradation by ligand-targeted enzymes: towards the creation of catalytic antagonists.
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Alcohol Dehydrogenase↗
Biomedical subjects
Benjamin G Davis
Publications and source records attributed to Benjamin G Davis.
Chemical modification of biocatalysts.
Although several powerful methods exist for the redesign of enzyme structure and function these are typically limited to the 20 most abundant proteinogenic amino acids. The use of chemical modification overcomes this limitation to allow virtually unlimited alteration of amino acid sidechain structures. If heterogeneous mixtures of enzyme products are to be avoided, however, the required chemistry should be efficient, selective and compatible with aqueous conditions. Recent advances have been made in the modification of proteinases, aminotransferases and redox enzymes.
Endopeptidases↗
Chemically modified "polar patch" mutants of subtilisin in peptide synthesis with remarkably broad substrate acceptance: designing combinatorial biocatalysts.
A significant enhancement of the applicability of the serine protease subtilisin Bacillus lentus (SBL) in peptide synthesis was achieved by using the strategy of combined site-directed mutagenesis and chemical modification to create chemically modified mutant (CMM) enzymes. The introduction of polar and/or homochiral auxiliary substituents, such as X=oxazolidinones, alkylammonium groups, and carbohydrates at position 166 at the base of the primary specificity S(1) pocket created SBL CMMs S166C-S-X with strikingly broad structural substrate specificities. These CMMs are capable of catalyzing the coupling reactions of not only L-amino acid esters but also D-amino acid esters as acyl donors with glycinamide to give the corresponding dipeptides in good yields. These powerful enzymes are also applicable to the coupling of L-amino acid acyl donors with alpha-branched acyl acceptor, L-alaninamide. Typical increases in isolated yields of dipeptides of 60-80 % over SBL-WT (e.g. 0 % yield of Z-D-Glu-GlyNH(2) using SBL-WT-->74 % using S166C-S-(CH(2))(2) NMe(3) (+)) demonstrate the remarkable synthetic utility of this "polar patch" strategy. Such wide-ranging systems displaying broadened and therefore similarly high, balanced yields of products (e.g. 91 % Z-L-Ala-GlyNH(2) and 86 % yield of Z-D-Ala-GlyNH(2) using S166C-S-(3R,4S)-indenooxazolidinone) may now allow the use of biocatalysts in parallel library synthesis.
Bacillus↗
Functional divergence in the glutathione transferase superfamily in plants. Identification of two classes with putative functions in redox homeostasis in Arabidopsis thaliana.
Searches with the human Omega glutathione transferase (GST) identified two outlying groups of the GST superfamily in Arabidopsis thaliana which differed from all other plant GSTs by containing a cysteine in place of a serine at the active site. One group consisted of four genes, three of which encoded active glutathione-dependent dehydroascorbate reductases (DHARs). Two DHARs were predicted to be cytosolic, whereas the other contained a chloroplast targeting peptide. The DHARs were also active as thiol transferases but had no glutathione conjugating activity. Unlike most other GSTs, DHARs were monomeric. The other class of GST comprised two genes termed the Lambda GSTs (GSTLs). The recombinant GSTLs were also monomeric and had glutathione-dependent thiol transferase activity. One GSTL was cytosolic, whereas the other was chloroplast-targeted. When incubated with oxidized glutathione, the putative active site cysteine of the GSTLs and cytosolic DHARs formed mixed disulfides with glutathione, whereas the plastidic DHAR formed an intramolecular disulfide. DHAR S-glutathionylation was consistent with a proposed catalytic mechanism for dehydroascorbate reduction. Roles for the cytosolic DHARs and GSTLs as antioxidant enzymes were also inferred from the induction of the respective genes following exposure to chemicals and oxidative stress.
Amino Acid Sequence↗
Novel cyclic sugar imines: carbohydrate mimics and easily elaborated scaffolds for aza-sugars.
[reaction: see text] Representative simple or polyhydroxylated, pyrrolidine (e.g, DRAM) or piperidine (e.g., DNJ) imines not only are potential carbohydrate-processing enzyme inhibitors that may be formed as regioisomeric variants but also are scaffolds that may be rapidly elaborated to diversely functionalized aza-sugars through highly diastereoselective organometallic additions.
Aza Compounds↗
Drug delivery systems based on sugar-macromolecule conjugates.
The specificity of carbohydrate-protein interactions can greatly outstrip that of many other ligand-binding systems; such is the enormous density of information that sugars can convey. In addition, macromolecules allow for the fine-tuning of active drug delivery through their great ability to undergo site-specific modification and their inherent physicochemical properties. Once combined, these two factors suggest that sugar-macromolecule conjugates, targeted using endogenous carbohydrate binding proteins, are a promising route to the 'magic bullet'.
Animals↗