Combinatorial discovery of peptide dendrimer enzyme models hydrolyzing isobutyryl fluorescein.

Two 6750-membered one-bead-one-compound peptide dendrimer combinatorial libraries L (X(4))(8)(LysX(3))(4)(LysX(2))(2)LysX(1) (X(1-4) = 14 different amino acids or deletion, Lys = branching lysine residue) and AcL (with N-terminal acetylation) were prepared by split-and-mix solid phase peptide synthesis. Screening toward fluorogenic substrates for esterase and aldolase activities using the in silica off-bead assay (N. Maillard et al., J. Comb. Chem. 2009, 11, 667-675) and bead decoding by amino acid analysis revealed histidine containing sequences active against fluorescein diacetate. Isobutyryl fluorescein, a related hydrophobic fluorogenic substrate, was preferentially hydrolyzed by dendrimers from library AcL containing hydrophobic residues such as AcH3 (AcHis)(8)(LysLeu)(4)(LysVal)(2)LysLysOH, compared to simple oligohistidine peptides as reference catalysts. Polycationic dendrimers from library L with multiple free N-termini such as H8 (His)(8)(LysßAla)(4)(LysThr)(2)LysaProNH(2) (aPro = (2S,4S)-4-aminoproline) showed stronger reactivity toward 8-acetoxypyrene-1,3,6-trisulfonate with partial acylation of N-termini. These experiments highlight the role of noncatalytic amino acids to determine substrate selectivity in peptide dendrimer esterase models.

Five-substrate cocktail as a sensor array for measuring enzyme activity fingerprints of lipases and esterases.

Substrate arrays for measuring enzyme activity fingerprints can be conveniently formulated as cocktails designed such that the reaction products can be separated and quantified by analytical high-performance liquid chromatography (HPLC). Fingerprinting of lipases and esterases, an important class of microbial enzymes, is reported with a cocktail of only five substrates as a practical fingerprinting reagent. An unusually strong C4-esterase activity was thus revealed in a recently discovered microbial esterase.

Bead diffusion assay for discovering antimicrobial cyclic peptides.

A combinatorial library of 15,536 cyclic decapeptide analogues of tyrocidine A and gramicidin S was prepared on photocleavable TentaGel beads. The beads were photolyzed without solvent, and spread onto an agar plate inoculated with bacterial lawn. Clear zones were formed around beads carrying antimicrobially active peptides such as E18 c(kVOrnLfThiYOrnLq), which inhibited growth of B. subtilis and selected MRSA strains.

Comparing dendritic with linear esterase peptides by screening SPOT arrays for catalysis.

Fluorescence screening of a 96-membered SPOT library of histidine containing dendritic and linear peptides revealed the remarkable esterolytic activity of short histidine oligomers that show catalytic proficiencies within one order of magnitude of histidine-containing esterase peptide dendrimers.

Identification of catalytic Peptide dendrimers by "off-bead" in silica high-throughput screening of combinatorial libraries.

A combinatorial library of up to 65'536 peptide dendrimers (AcX(8)X(7))(8)(DapX(6)X(5))(4)(DapX(4)X(3))(2)DapX(2)X(1) (Dap = (S)-2,3-diaminopropionic acid branching point, X(8-1) = groups of four proteinogenic l-amino acids) was prepared on a photocleavable tentagel resin. The library was assayed for catalytic hydrolysis of the fluorogenic substrate 1-butyryloxy-pyrene-2,7,8-trisulfonate 1 and analogs by a simple procedure involving (a) photocleavage from the support in the absence of solvent, (b) spreading of the solid support beads on the surface of a silicagel plate impregnated with an aqueous buffered substrate solution, and (c) identification of hits as beads surrounded by a fluorescent halo indicative of catalysis and sequence determination in hits and nonhits by amino acid analysis of the beads. The experiment provides direct access to structure-activity relationships in the library and delivers active esterase dendrimers. Anionic glutamate residues in the outer dendrimer branches were found to inhibit catalysis by histidine residues at the dendrimer core. The "off-bead" in silica assay is simple to implement and transferable to other library and reaction types.

Combinatorial libraries of peptide dendrimers: design, synthesis, on-bead high-throughput screening, bead decoding and characterization.

Dendrimers are branched synthetic macromolecules. This protocol describes the synthesis (1-2 weeks), functional screening (1.5 d) and decoding (2 d) of 'one-bead-one-compound' combinatorial libraries of dendrimers assembled from amino-acid building blocks by 'split-and-mix' solid phase peptide synthesis. The method resembles that for synthesizing linear peptides, except that a branching diamino acid is used at every third position to obtain the dendritic structure. Structural diversification by splitting is restricted to four amino acids per variable position, yielding libraries of approximately 60,000 sequences. In such libraries, the sequence of a dendrimer can be deduced uniquely from an amino-acid analysis of the solid support bead. This analysis is more reliable, faster and far less costly than Edman sequencing such that decoding multiple beads is affordable. The method is exemplified for the identification of catalytic peptide dendrimers catalyzing the hydrolysis of acyloxypyrene-trisulfonates with substrate binding (K(M) = 10-300 microM) and rate accelerations up to k(cat)/k(uncat) = 10(4) in aqueous buffer.

Enzyme assays.

Enzyme assays are analytical tools to visualize enzyme activities. In recent years a large variety of enzyme assays have been developed to assist the discovery and optimization of industrial enzymes, in particular for "white biotechnology" where selective enzymes are used with great success for economically viable, mild and environmentally benign production processes. The present article highlights the aspects of fluorogenic and chromogenic substrates, sensors, and enzyme fingerprinting, which are our particular areas of interest.

A cyclodecapeptide ligand to vitamin B12.

Libraries of cyclic decapeptides were screened with vitamin B(12) derivatives to give cyclic peptide ligands incorporating histidine and cysteine as coordinating residues and negatively charged amino acids. Two hits, cyclo-(HisAspGluProGlyIleAlaThrProdGln) and cyclo-(ValAspGluProGlyGluAspCysProdGln) were resynthesized in good yields for solution experiments. The peptides bind aquocobalamin with coordination of His or Cys to the cobalt with high affinities (K(a) approximately 10(5) M(-1)). Additional interactions between the peptide side chains and the vitamin B(12) corrin moiety were determined by studying the (1)H NMR solution structure. The cyclopeptide-cobalamin complex with the histidine residue showed enhanced stability towards cyanide exchange, demonstrating the shielding effect of the ligand on the metal center.