[Show abstract][Hide abstract] ABSTRACT: Ligand-binding epitopes of proteins can mutate rapidly, as shown by viral mutations that lead to escape from neutralizing antibodies. We have undertaken to recreate in vitro the evolutionary competition between viral mutations that allow escape from antibody binding and host mutations that generate new neutralizing antibodies to the mutated viral antigen. To examine this vital race, we describe a phage-based method that allows rapid analysis of molecules that perturb the binding of proteins to their ligands. Because the system can amplify by replication, single-molecule sensitivity can be achieved. When combinatorial protein or small-molecule libraries are studied, large numbers of binding events can be analyzed simultaneously. Such libraries may be used in a sequential phage escape format, where cycles of phage binding and release of mutants are driven by antibodies or small molecules and the difficulty of escape increases at each cycle. Ultimately, the sequencing of the viral mutants allows annotation of the allowed trajectory of escape. Likewise, sequencing of the antibody perturbants charts the chemistry of the immune system response to the viral challenge. We have termed such analysis of competing mutations a "checkmate analysis." When viral systems are studied, a checkmate analysis allows experimental evaluation of the evolutionary contest between viruses and the immune system and may predict which antibodies and small-molecule ligands should be generated in anticipation of viral mutations before these mutations create viral epidemics.
Proceedings of the National Academy of Sciences 08/2007; 104(31):12703-8. DOI:10.1073/pnas.0705362104 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cocaine is a powerful and addictive stimulant whose abuse remains a prevalent health and societal crisis. Unfortunately, no pharmacological therapies exist and therefore alternative protein-based therapies have been examined. One such approach is immunopharmacotherapy, wherein antibodies are utilized to either bind or hydrolyze cocaine thereby blocking it from exerting its euphoric effect. Towards this end, antibodies capable of binding and hydrolyzing cocaine were identified by phage display from a biased single chain antibody library generated from the spleens of mice previously immunized with a cocaine phosphonate transition state analog hapten. Two classes of antibodies emerged based on sequence homology and mode of action. Alanine scanning mutagenesis and kinetic analysis revealed that residues H97, H99, and L96 are crucial for antibodies 3F5 and 3H9 to accelerate the hydrolysis of cocaine. Antibodies 3F1 through 3F4, which are similar to our previously identified 3A6 class of antibodies, catalyze hydrolysis through transition state stabilization by tyrosine or histidine residues H50 and L94. Mutation of either one or both tyrosine residues to histidine conferred hydrolytic activity on previously inactive antibody 3F4. Mutational analysis of residue H50 of antibody 3F3 resulted in a glutamine mutant with a rate enhancement three times greater than wild-type. A double mutant, containing glutamineH50 and lysineH52, showed a tenfold rate enhancement over wild-type. These results indicate the power of initial selection of catalytic antibodies from a biased antibody library in both rapid generation and screening of mutants for improved catalysis.
[Show abstract][Hide abstract] ABSTRACT: Taxol (Paclitaxel) is an important natural product for the treatment of solid tumors. Despite a well documented tubulin-stabilizing effect, many side effects of taxol therapy cannot be explained by cytoskeletal mechanisms. In the present study submicromolar concentrations of taxol, mimicking concentrations found in patients, induced cytosolic calcium (Ca(2+)) oscillations in a human neuronal cell line. These oscillations were independent of extracellular and mitochondrial Ca(2+) but dependent on intact signaling via the phosphoinositide signaling pathway. We identified a taxol binding protein, neuronal Ca(2+) sensor 1 (NCS-1), a Ca(2+) binding protein that interacts with the inositol 1,4,5-trisphosphate receptor from a human brain cDNA phage display library. Taxol increased binding of NCS-1 to the inositol 1,4,5-trisphosphate receptor. Short hairpin RNA-mediated knockdown of NCS-1 in the same cell line abrogated the response to taxol but not to other agonists stimulating the phosphoinositide signaling pathway. These findings are important for studies involving taxol as a research tool in cell biology and may help to devise new strategies for the management of side effects induced by taxol therapy.
Proceedings of the National Academy of Sciences 12/2006; 103(48):18356-61. DOI:10.1073/pnas.0607240103 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Antibody 7A1 hydrolyzes cocaine to produce nonpsychoactive metabolites ecgonine methyl ester and benzoic acid. Crystal structures of 7A1 Fab' and six complexes with substrate cocaine, the transition state analog, products ecgonine methyl ester and benzoic acid together and individually, as well as heptaethylene glycol have been analyzed at 1.5-2.3 angstroms resolution. Here, we present snapshots of the complete cycle of the cocaine hydrolytic reaction at atomic resolution. Significant structural rearrangements occur along the reaction pathway, but they are generally limited to the binding site, including the ligands themselves. Several interacting side chains either change their rotamers or alter their mobility to accommodate the different reaction steps. CDR loop movements (up to 2.3 angstroms) and substantial side chain rearrangements (up to 9 angstroms) alter the shape and size (approximately 320-500 angstroms3) of the antibody active site from "open" to "closed" to "open" for the substrate, transition state, and product states, respectively.
[Show abstract][Hide abstract] ABSTRACT: An autoinducer arising from reaction of cyclized S-DPD and carbonate is shown to induce light in V. harveyi and thus may play a previously unknown role in quorum sensing.
Chemical Communications 11/2005; 38(38):4863-5. DOI:10.1039/b509396a · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Quorum sensing activity was investigated in the bacterium Vibrio harveyi using a series of both natural and nonnatural analogs of DPD, the penultimate precursor to autoinducer AI-2. The progression of molecules that were both synthesized and investigated includes enantiomeric variants, carbon-chain extension, and hydroxyl-functional group addition/deletions of DPD. The compilation of these studies reveals a binding cleft that can accommodate a number of different structural variants of DPD, albeit with invariably lower activities.
[Show abstract][Hide abstract] ABSTRACT: Putting on a good display: A novel selection protocol was devised for the simultaneous display cloning of three homologues of the FK506-binding protein (FKBP12, FKBP12.6, and FKBP13) by using AP1497 (see structure), a mimetic of FK506, and a T7 complementary-DNA phage-display library. A quantitative onphage binding assay was also performed to evaluate the affinity of the isolated proteins.
[Show abstract][Hide abstract] ABSTRACT: Chemical communication ("quorum sensing") amongst bacteria has been studied by the synthesis and study of enantiopure (R)-4,5-dihydroxy-2,3- pentanedione (DPD, see scheme). Bioactivity assays with DPD have shown that chelation of boron by the cyclic form of DPD appears to be essential for full induction of bioluminescence, which is an example of quorum-sensing-controlled behavior.
[Show abstract][Hide abstract] ABSTRACT: The identification of cellular targets has traditionally been the starting point for natural product mode of action studies and has led to the understanding of many biological processes. Conventional experimental approaches have depended on cell-based screening and/or affinity chromatography. Although both of these techniques aid in the discovery of protein cellular targets, a method that couples protein identification with gene isolation would be extremely valuable.
A procedure for the direct cloning of cellular proteins, based on their affinity for natural products, using cDNA phage display has been developed. The technique is referred to as display cloning because it involves the cloning of proteins displayed on the surface of a bacteriophage particle. The approach has been established by isolating a full-length gene clone of FKBP12 (FK506-binding protein) from a human brain cDNA library using a biotinylated FK506 probe molecule. During the affinity selection, the FKBP12 gene emerged as the dominant library member and was the only sequence identified after the second round of selection.
The development of display cloning greatly facilitates the investigation of ligand-receptor interaction biology and natural product mode of action studies. This procedure utilizes heterologous protein display on infectious phage, which allows the amplification and repeated selection of putative sequences, leading to unambiguous target identification. In addition, the direct connection of a functional protein to its gene sequence eliminates the subsequent cloning step required with tissue homogenate or cell lysate affinity methods, allowing direct isolation of an expressible gene sequence.