A strategy for designing "multi-prong" enzyme inhibitors by incorporating selective ligands to the liposomal surface.

We offer a novel strategy for designing "multi-prong" inhibitors of enzymes by incorporating selective ligands on the liposomal surface.

Inhibition of matrix metalloproteinase-9 by "multi-prong" surface binding groups.

A novel strategy of blocking the active site accessibility of MMP-9 by "multi-prong" surface binding groups is described.

Spacer-based selectivity in the binding of "two-prong" ligands to recombinant human carbonic anhydrase I.

Benzenesulfonamide and iminodiacetate (IDA)-conjugated Cu(2+) independently interact at the active site and a peripheral site of carbonic anhydrases, respectively [Banerjee, A. L., Swanson, M., Roy, B. C., Jia, X., Haldar, M. K., Mallik, S., and Srivastava, D. K. (2004) J. Am. Chem. Soc. 126, 10875-10883]. By attaching IDA-bound Cu(2+) to benzenesulfonamide via different chain length spacers, we synthesized two "two-prong" ligands, L1 and L2, in which the distances between Cu(2+) and NH(2) group of sulfonamide were 29 and 22 A, respectively. We compared the binding affinities of L1 and L2, vis-a-vis their parent compound, benzenesulfonamide, for recombinant human carbonic anhydrase I (hCA-I) by performing the fluorescence titration and steady-state kinetic experiments. The experimental data revealed that whereas the binding affinity of L1 for hCA-I was similar to that of benzenesulfonamide, the binding affinity of L2 was approximately 2 orders of magnitude higher, making L2 one of the most potent ligands or inhibitors of hCA-I. Since the enhanced binding or inhibitory potency of L2 is diminished (to the level of benzenesulfonamide) either in the presence of EDTA or upon treatment of the enzyme with diethyl pyrocarbonate, it is proposed that Cu(2+) of L2 interacts with one of the surface-exposed histidine residues of the enzyme. A cumulative account of the experimental data leads to the suggestion that the differential binding of L1 versus L2 to hCA-I is encoded in the chain length of the spacer moiety.

Solid-supported synthesis of polymerizable lanthanide-ion chelating lipids for protein detection.

Usually, lipids are synthesized employing solution-phase organic synthesis techniques. Though successful, the purifications can be difficult to accomplish due to the amphiphilic nature of the molecules. Herein, we demonstrate the advantages of a solid-phase approach for preparing a variety of metal-chelating lipids. A number of saturated and polymerizable metal-chelating lipids were prepared using this methodology. This approach requires one chromatographic purification after cleaving the lipids from the solid support. We also demonstrate that the resulting polymerized liposomes (containing Eu3+) possess the appropriate luminescence properties for the qualitative and quantitative determination of proteins.

Evaluation of two lanthanide complexes for qualitative and quantitative analysis of target proteins via partial least squares analysis.

Two lanthanide complexes, namely 5-aminosalicylic acid ethylenediaminetetraacetate europium(III) (5As-EDTA-Eu3+) and 4-aminosalicylic acid ethylenediaminetetraacetate terbium(III), were evaluated for the analysis of carbonic anhydrase, human serum albumin (HSA), and gamma-globulin. Quantitative analysis is based on their luminescence enhancement upon protein binding and qualitative analysis on their lifetime capability to recognize the binding protein. Analytical figures of merit are presented for the three proteins. The limits of detection with 5As-EDTA-Eu3+ are at the parts per billion level. Partial least square regression analysis is used to determine HSA and gamma-globulin in binary mixtures without previous separation at the concentration ranges typically found in clinical tests of human blood serum.

Two-prong inhibitors for human carbonic anhydrase II.

The enzyme inhibitors are usually designed by taking into consideration the overall dimensions of the enzyme's active site pockets. This conventional approach often fails to produce desirable affinities of inhibitors for their cognate enzymes. To circumvent such constraints, we contemplated enhancing the binding affinities of inhibitors by attaching tether groups, which would interact with the surface exposed amino acid residues. This strategy has been tested for the inhibition of human carbonic anhydrase II. Benzenesulfonamide serves as a weak inhibitor for the enzyme, but when it is conjugated to iminodiacetate-Cu2+ (which interacts with the surface-exposed His residues) via a spacer group, its binding affinity is enhanced by about 2 orders of magnitude. This "two-prong" approach is expected to serve as a general strategy for converting weak inhibitors of enzymes into tight-binding inhibitors.

Protein surface-assisted enhancement in the binding affinity of an inhibitor for recombinant human carbonic anhydrase-II.

We elaborate on a novel strategy for enhancing the binding affinity of an active-site directed inhibitor by attaching a tether group, designed to interact with the surface-exposed histidine residue(s) of enzymes. In this approach, we have utilized the recombinant form of human carbonic anhydrase-II (hCA-II) as the enzyme source and benzenesulfonamide and its derivatives as inhibitors. The steady-state kinetic and the ligand binding data revealed that the attachment of iminodiacetate (IDA)-Cu(2+) to benzenesulfonamide (via a triethylene glycol spacer) enhanced its binding affinity for hCA-II by about 40-fold. No energetic contribution of either IDA or triethylene glycol spacer was found (at least in the ground state of the enzyme-inhibitor complex) when Cu(2+) was stripped off from the tether group-conjugated sulfonamide derivative. Arguments are presented that the overall strategy of enhancing the binding affinities of known inhibitors by attaching the IDA-Cu(2+) groups to interact with the surface-exposed histidine residues will find a general application in designing the isozyme-specific inhibitors as potential drugs.

An investigation on the analytical potential of polymerized liposomes bound to lanthanide ions for protein analysis.

We present a promising approach to protein sensing based on Eu3+ ions incorporated into polymerized liposomes. The sensitization of Eu3+ is accomplished with 5-aminosalicylic acid, which provides energy transfer for a stable reference signal and a wide wavelength excitation range free from protein interference. The lipophilic character of polymerized liposomes provides the appropriate platform for protein interaction with the lanthanide ion. Quantitative analysis is based on the linear relationship between the luminescence signal of Eu3+ and protein concentration. Because no spectral shift of the lanthanide luminescence is observed upon protein interaction, qualitative analysis is based on the luminescence lifetime of polymerized liposomes. This parameter, which changes significantly upon protein-liposome interaction, follows a well-behaved single-exponential decay that might be useful for protein identification.

Conjugation of poor inhibitors with surface binding groups: a strategy to improve inhibition.

Conjugation of surface binding groups with inhibitors for carbonic anhydrase leads to the conversion of weak inhibitors to strong inhibitors.

Synthesis of metal-chelating lipids to sensitize lanthanide ions.

Sensitization of lanthanide ions is important for lanthanide ion-based assays and sensing. To the best of our knowledge, there are very few reports of lanthanide ion sensitization after it is incorporated into the liposome surface. This paper describes the syntheses of several saturated and polymerizable metal-chelating lipids based on chelidamic acid. The lipids are synthesized either from (S)-ornithine or racemic 2,3-diaminopropanoic acid. These lipids as well as polymerized liposomes incorporating these lipids sensitize lanthanide ions. Liposomes from the lipid 18-Eu(3+) provided a probe that relies not only on the emission wavelengths of Eu(3+) but also on a reproducible lifetime that can be used for protein identification.

Synthesis of new, pyrene-containing, metal-chelating lipids and sensing of cupric ions.

The syntheses of several saturated, pyrene-containing, metal-chelating lipids are described. These lipids are capable of strongly binding to transition metal ions employing the metal-chelating headgroup. The excimer-to-monomer ratio of the pyrene groups changes with addition of cupric ions to the liposomes. Three other transition metal ions (Zn(2+), Ni(2+), and Hg(2+)) did not cause any appreciable changes in the excimer-to-monomer ratio. [reaction--see text]

Thermodynamic studies on the recognition of flexible peptides by transition-metal complexes.

Strong and selective binding to a trihistidine peptide has been achieved employing Cu(2+)-histidine interactions in aqueous medium (25 mM HEPES buffer, pH 7.0). When the pattern of cupric ions on a complex matched with the pattern of histidines on the peptide, a strong and selective binding was observed. UV-vis spectroscopic studies show that the cupric ions coordinate to the histidines of the peptides. Thermodynamic studies reveal that the binding process is enthalpy driven over the entire range of working temperature (25-40 degrees C). An enthalpy-entropy compensation effect was also observed.