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  • Gutierrez Arenas, Omar, et al. (författare)
  • Detection of competitive enzyme inhibition with end point progress curve data
  • 2006
  • Ingår i: Analytical Biochemistry. - 0003-2697 .- 1096-0309. ; 358:1, s. 11-19
  • Tidskriftsartikel (refereegranskat)abstract
    • A model for a dimensionless factor, the inhibition detection limit (IDL), which describes the limit of detection of competitive inhibition for end point assays as a function of the proportion of substrate converted into product, has been developed. For a given end point enzymatic assay, the IDL function has a maximum that is dependent on the error structure parameters (four parameters) of the assay, the value of [S]o/K(ms), and the extent of product inhibition (K(ms)/K(mp)). Accordingly, the substrate conversion level that maximized the ability to detect samples with high Ki/[I] ratios was predicted for each member of a population of simulated assays. Furthermore, we identified a consensus substrate conversion level where the probability of a near-optimal robustness and detection limit for all the members of the assay population is maximal. Unlike the optimal substrate conversion level for individual assays, this consensus substrate conversion level was dependent only on [S]o/K(m), K(ms)/K(mp), and whether the signal increases or decreases during the course of the reaction. Consensus substrate conversion levels were beyond the initial velocity range for almost all the analyzed assay populations. It was shown that the IDL factor was a more informative indicator of assay quality than the popular Z' factor.
  • Nosrati, Masoumeh, et al. (författare)
  • Insights from engineering the Affibody-Fc interaction with a computational-experimental method
  • 2017
  • Ingår i: Protein Engineering Design & Selection. - : Oxford University Press. - 1741-0126 .- 1741-0134. ; 30:9, s. 593-601
  • Tidskriftsartikel (refereegranskat)abstract
    • The interaction between the Staphylococcal Protein A (SpA) domain B (the basis of the Affibody) molecule and the Fc of IgG is key to the use of Affibodies in affinity chromatography and in potential therapies against certain inflammatory diseases. Despite its importance and four-decade history, to our knowledge this interaction has never been affinity matured. We elucidate reasons why single-substitutions in the SpA which improve affinity to Fc may be very rare, and also discover substitutions which potentially serve several engineering purposes. We used a variation of FoldX to predict changes in protein-protein-binding affinity, and produce a list of 41 single-amino acid substitutions on the SpA molecule, of which four are near wild type (wt) and five are at most a factor of four from wt affinity. The nine substitutions include one which removes lysine, and several others which change charge. Subtle modulations in affinity may be useful for modifying column elution conditions. The method is applicable to other protein-protein systems, providing molecular insights with lower workload than existing experimental techniques.
  • Andersson, H.O., et al. (författare)
  • Optimization of P1-P3 groups in symmetric and asymmetric HIV-1 protease inhibitors
  • 2003
  • Ingår i: European Journal of Biochemistry. - 0014-2956 .- 1432-1033. ; 270:8, s. 1746-1758
  • Tidskriftsartikel (refereegranskat)abstract
    • HIV-1 protease is an important target for treatment of AIDS, and efficient drugs have been developed. However, the resistance and negative side effects of the current drugs has necessitated the development of new compounds with different binding patterns. In this study, nine C-terminally duplicated HIV-1 protease inhibitors were cocrystallised with the enzyme, the crystal structures analysed at 1.8-2.3 Å resolution, and the inhibitory activity of the compounds characterized in order to evaluate the effects of the individual modifications. These compounds comprise two central hydroxy groups that mimic the geminal hydroxy groups of a cleavage-reaction intermediate. One of the hydroxy groups is located between the d-oxygen atoms of the two catalytic aspartic acid residues, and the other in the gauche position relative to the first. The asymmetric binding of the two central inhibitory hydroxyls induced a small deviation from exact C2 symmetry in the whole enzyme-inhibitor complex. The study shows that the protease molecule could accommodate its structure to different sizes of the P2/P2' groups. The structural alterations were, however, relatively conservative and limited. The binding capacity of the S3/S3' sites was exploited by elongation of the compounds with groups in the P3/P3' positions or by extension of the P1/P1' groups. Furthermore, water molecules were shown to be important binding links between the protease and the inhibitors. This study produced a number of inhibitors with Ki values in the 100 picomolar range.
  • Dahl, Göran, et al. (författare)
  • Hepatitis C virus NS3 protease is activated by low concentrations of protease inhibitors
  • 2009
  • Ingår i: Biochemistry. - 0006-2960 .- 1520-4995. ; 48:48, s. 11592-11602
  • Tidskriftsartikel (refereegranskat)abstract
    • The nonstructural protein 3 (NS3) of hepatitis C virus (HCV) is a bifunctional enzyme with a protease and a helicase functionality located in each of the two domains of the single peptide chain. There is little experimental evidence for a functional role of this unexpected arrangement since artificial single domain forms of both enzymes are catalytically competent. We have observed that low concentrations of certain protease inhibitors activate the protease of full-length NS3 from HCV genotype 1a with up to 100%, depending on the preincubation time and the inhibitor used. The activation was reduced, but not eliminated, by increased ionic strength, lowered glycerol concentration, or lowered pH. In all cases, it was at the expense of a significant loss of activity. Activation was not seen with the artificial protease domain of genotype 1b NS3 fused with a fragment of the NS4A cofactor. This truncated and covalently modified enzyme form was much less active and exhibited fundamentally different catalytic properties to the full-length NS3 protease without the fused cofactor. The most plausible explanation for the activation was found to involve a slow transition between two enzyme conformations, which differed in their catalytic ability and affinity for inhibitors. Equations derived based on this assumption resulted in better fits to the experimental data than the equation for simple competitive inhibition. The mechanism may involve an inhibitor-induced stabilization of the helicase domain in a conformation that enhances the protease activity, or an improved alignment of the catalytic triad in the protease. The proposed mnemonic mechanism and derived equations are viable for both these explanations and can serve as a basic framework for future studies of enzymes activated by inhibitors or other ligands.
  • Elinder, Malin, et al. (författare)
  • Experimental Validation of a Fragment Library for Lead Discovery Using SPR Biosensor Technology
  • 2011
  • Ingår i: Journal of Biomolecular Screening. - 1087-0571 .- 1552-454X. ; 16:1, s. 15-25
  • Tidskriftsartikel (refereegranskat)abstract
    • A new fragment library for lead discovery has been designed and experimentally validated for use in surface plasmon resonance (SPR) biosensor-based screening. The 930 compounds in the library were selected from 4.6 million commercially available compounds using a series of physicochemical and medicinal chemistry filters. They were screened against 3 prototypical drug targets: HIV-1 protease, thrombin and carbonic anhydrase, and a nontarget: human serum albumin. compound solubility was not a problem under the conditions used for screening. The high sensitivity of the sensor surfaces allowed the detection of interactions for 35% to 97% of the fragments, depending on the target protein. None of the fragments was promiscuous (i.e., interacted with a stoichiometry ≥5:1 with all 4 proteins), and only 2 compounds dissociated slowly from all 4 proteins. The use of several targets proved valuable since several compounds would have been disqualified from the library on the grounds of promiscuity if fewer target proteins had been used. The experimental procedure allowed an efficient evaluation and exploration of the new fragment library and confirmed that the new library is suitable for SPR biosensor-based screening.
  • Elinder, Malin, 1977-, et al. (författare)
  • Screening for NNRTIs with Slow Dissociation and High Affinity for a Panel of HIV-1 RT Variants
  • 2009
  • Ingår i: Journal of Biomolecular Screening. - : SAGE. - 1087-0571 .- 1552-454X. ; 14:4, s. 395-403
  • Tidskriftsartikel (refereegranskat)abstract
    • A lead optimization library consisting of 800 HIV-1 nonnucleoside reverse transcriptase inhibitors (NNRTIs) was screened in parallel against 4 clinically relevant variants of HIV-1 RT (Wt, L100I, Y181C, and K103N) using a surface plasmon resonance-based biosensor. the aim was to identify inhibitors suitable in specific topical microbicides efficient for preventing the transmission of a range of clinically significant strains of HIV-1. the authors hypothesized that such compounds should have high affinity and slow dissociation rates for multiple variants of the target. to efficiently analyze the large amount of real-time data (sensorgrams) that were generated in the  screening, they initially used signals from 3 selected time points to identify compounds with high affinity and slow dissociation for the   complete panel of enzyme variants. hits were confirmed by visually  inspecting the complete sensorgrams. two structurally unrelated   compounds fulfilled the hit criteria, but only 1 compound was found to   (a) compete with a known NNRTI for binding to the NNRTI site, (b)   inhibit HIV-1 RT activity, and (c) inhibit HIV-1 replication in cell culture, for all 4 enzyme variants. this novel screening methodology offers high-resolution real-time kinetic data for multiple targets in parallel. it is expected to have broad applicability for the discovery of compounds with defined kinetic profiles, crucial for optimal therapeutic effects.
  • Hämäläinen, Markku D., et al. (författare)
  • Characterization of a set of HIV-1 protease inhibitors using binding kinetics data from a biosensor-based screen
  • 2000
  • Ingår i: Journal of Biomolecular Screening. - 1087-0571 .- 1552-454X. ; 5:5, s. 353-359
  • Tidskriftsartikel (refereegranskat)abstract
    • The interaction between 290 structurally diverse human immunodeficiency virus type 1 (HIV-1) protease inhibitors and the immobilized enzyme was analyzed with an optical biosensor, Although only a single concentration of inhibitor was used, information about the kinetics of the interaction could be obtained by extracting binding signals at discrete time points. The statistical correlation between the biosensor binding data, inhibition of enzyme activity (K-i), and viral replication (EC50) revealed that the association and dissociation rates for the interaction could be resolved and that they were characteristic for the compounds. The most potent inhibitors, with respect to K-i and EC50 values, including the clinically used drugs, all exhibited fast association and slow dissociation rates. Selective or partially selective binders for HIV-1 protease could be distinguished from compounds that showed a general protein-binding tendency by using three reference target proteins. This biosensor-based direct binding assay revealed a capacity to efficiently provide high-resolution information on the interaction kinetics and specificity of the interaction of a set of compounds with several targets simultaneously.
  • Lundquist, Anna, et al. (författare)
  • Biotinylated lipid bilayer disks as model membranes for biosensor analyses
  • 2010
  • Ingår i: Analytical Biochemistry. - 0003-2697 .- 1096-0309. ; 405:2, s. 153-159
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to investigate the potential of polyethylene glycol (PEG)-stabilized lipid bilayer disks as model membranes for surface plasmon resonance (SPR)-based biosensor analyses. Nanosized bilayer disks that included 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)(2000)] (DSPE-PEG(2000)-biotin) were prepared and structurally characterized by cryo-transmission electron microscopy (cryo-TEM) imaging. The biotinylated disks were immobilized via streptavidin to three different types of sensor chips (CM3, CM4, and CM5) varying in their degree of carboxymethylation and thickness of the dextran matrix. The bilayer disks were found to interact with and bind stably to the streptavidin-coated sensor surfaces. As a first step toward the use of these bilayer disks as model membranes in SPR-based studies of membrane proteins, initial investigations were carried out with cyclooxygenases 1 and 2 (COX 1 and COX 2). Bilayer disks were preincubated with the respective protein and thereafter allowed to interact with the sensor surface. The signal resulting from the interaction was, in both cases, significantly enhanced as compared with the signal obtained when disks alone were injected over the surface. The results of the study suggest that bilayer disks constitute a new and promising type of model membranes for SPR-based biosensor studies.
  • Nordström, Helena, et al. (författare)
  • Identification of MMP-12 Inhibitors by Using Biosensor-Based Screening of a Fragment Library
  • 2008
  • Ingår i: Journal of Medicinal Chemistry. - 0022-2623 .- 1520-4804. ; 51:12, s. 3449-3459
  • Tidskriftsartikel (refereegranskat)abstract
    • Small inhibitors of matrix metalloproteinase 12 (MMP-12) have been identified with a biosensor-based screening strategy and a specifically designed fragment library. The interaction between fragments and three variants of the target and a reference protein with an active-site zinc ion was measured continuously by surface plasmon resonance. The developed experimental design overcame the inherent instability of MMP-12 and allowed the identification of fragments that interacted specifically with the active-site of MMP-12 but not with the reference protein. The interaction with MMP-12 for selected compounds were analyzed for concentration dependence and saturability. Compounds interacting distinctly with the target were further evaluated by an activity-based assay, verifying MMP-12 inhibition. Two effective inhibitors were identified, and the compound with highest affinity was confirmed to be a competitive inhibitor with an IC50 of 290 nM and a ligand efficiency of 0.7 kcal/mol heavy atom. This procedure integrates selectivity and binding site identification into the screening procedure and does not require structure determination.
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