ISSN:0021-2148    

DOI:10.1002/ijch.199600017

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA panel of catalytic antibodies which catalyze ester hydrolysis, transesterification, porphyrin metallation, Diels‐Alder, and redox reactions has been selected for crystallographic study. While these examples are only a handful of the catalytic antibodies generated to date, they represent distinct and important aspects of antibody catalysis. Since the first reports of catalysis, a great deal of progress has been made with respect to the scope, selectivity, and efficiency of antibody catalysis and strategies for generating catalytic antibodies. However, it is clear that further progress in the field will benefit greatly from a detailed understanding of the molecular interactions occurring in the combining site. High‐resolution crystallographic data should allow the importance of general base catalysis, entropy effects, electrophilic catalysis, and transition‐state stabilization to be evaluated. Antibody and enzyme active sites have been shown to share considerable structural and mechanistic similarity, and ongoing structure‐function studies of catalytic antibodies may enhance our understanding of the mechanisms and evolution of enzymatic catalysis. Structural studies of antibodies which perform a biological or highly selective reactions should enhance our ability to generate catalysts for important synthetic applications. Finally, the combination of high‐resolution crystallographic analysis with rational mutagenesis should provide a basis for engineering antibodies with enhanced p

ISSN:0021-2148    

DOI:10.1002/ijch.199600018

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe three‐dimensional structures of four catalytic antibodies, three of which were complexed with transition‐state analogs, have been determined by X‐ray crystallographic methods. An additional catalytic antibody structure has been deduced using homology modeling methods, and the information derived from the resulting model has been the basis for site‐directed mutagenesis experiments. Analysis of these crystal structures suggests that the primary source of catalytic activity in three of the antibodies is primarily shape and charge complementarity between the combining sites and the transition‐state‐analog haptens. The fourth structure may contain a modified “catalytic triad,” with histidine, serine, and tyrosine side chains positioned so that they could participate in the chemical transformation. Otherwise, the abzyme structures are representative of antibody structures in general, and do not possess any particularly unusual features that would suggest a classification outside the normal range of variation expected within the immunoglobulin family. Rather, the catalytic activity of these antibodies can be explained entirely on the basis of the local arrangement of residues that line the binding sites for their haptenic antigens. In addition, the structures provide strong evidence that the conserved immunoglobulin framework can provide a highly suitable context to serve as the basis for a generalized, progra

ISSN:0021-2148    

DOI:10.1002/ijch.199600019

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAntibody CNJ206 catalyzes the hydrolysis ofp‐nitrophenyl esters with significant rate enhancement and product specificity. We report here kinetic and affinity measurements for this antibody in the pH 4–9.5 range. We also report the X‐ray structures of CNJ206 Fab liganded with a transition‐state analog (TSA) and with one of the products of the hydrolysis,p‐nitrophenol, at pH 4. This product binds in the same hydrophobic pocket as thep‐nitrophenyl part of the TSA; its release at basic pH, where catalysis is usually measured, is facilitated by its ionized state and this avoids product inhibition. The conformation of the CNJ206 combining site is identical in this structure and in the previously determined structure of a CNJ206 Fab•TS A complex at pH 8. Taken together with the pH‐profile of the rate enhancement by CNJ206, the structural data support a mechanism for catalysis by CNJ206 involving stabilization of a tetrahedral oxyanion intermediate by the peptide NH groups of two consecutive residues in the H3 complementarity‐d

ISSN:0021-2148    

DOI:10.1002/ijch.199600020

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAntibody 1E9 catalyzes the bimolecular Diels–Alder reaction between tetrachlorothiophene dioxide andN‐ethylmaleimide with high catalytic efficiency. The genes encoding the heavy and light chains were cloned, sequenced, and expressed as a mouse/human chimera in a murine hybridoma. Comparison with the closely related and structurally characterized anti‐progesterone antibody DB3 has permitted identification of the residues that are likely to line the binding cavity. In addition to confirming the expectation of a highly hydrophobic active site, modeling results suggest that shape complementarity, achieved mainly through van der Waals rather than hydrogen bonding or electrostatic interactions, is likely to be the dominant factor in achieving effective preorganization of the substrates for catalysis. These conclusions can now be investigated through targeted mutagenesis of the putative active site residues exploiting the mammalian expression s

ISSN:0021-2148    

DOI:10.1002/ijch.199600021

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe solvolysis of a range of esters of 2‐methylbenzyl alcohol10has been studied. It was found that sulphonate esters are solvolyzed very rapidly in aqueous solution (t1/2≈ 35 s), whereas sulphinates react slowly (t1/2≈ 35 h) and a phosphonate diester is stable. The fluorescent 5‐dimethylaminonaphthalene‐1‐sulphinate (dansinate) esters (e.g.22) held the most promise as substrates for antibody‐catalyzed cationic cyclizations. It was shown by18O‐labeling studies that ester 13 is hydrolyzed predominantly (but not exclusively) by SN1 reaction at the benzylic position.A number of conditions were tried to effect cationic cyclizations of an unsaturated benzylic alcohol 26, whose ester is intended as the substrate for the antibody‐catalyzed reaction. The products obtained were the result of attack of the non‐benzylic alcohol on either the benzylic cation, to give 31 and 32, or on the protonated alkene, to give 29. No cyclization of the alkene onto the benzylic cation, to give 4, was observed, suggesting that this is a disfavored r

ISSN:0021-2148    

DOI:10.1002/ijch.199600022

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe catalytic activity of the antibody H11 is shown to reside chiefly in its ability to hydrolyze 1‐acetoxybutadiene to crotonaldehyde and to promote the cycloaddition of the intermediate enol withN‐alkylmaleimides. This conclusion is based upon the demonstration that the enol tautomerizes too rapidly in solution to be a competent intermediate and that under the reaction conditions for H11, no cycloaddition occurs with crotonaldehyde andN‐ethylmaleimide. As a first step towards a structural understanding of the chemistry of H11, chemical modification experiments have shown that reactions of acidic amino acids, tyrosine, lysine, and histidine, but not arginine, inhibit the reactions mediated b

ISSN:0021-2148    

DOI:10.1002/ijch.199600023

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThree benzisoxazole haptens designed to elicit antibody binding sites with widely differing polarity have been synthesized and used to induce antibodies in mice. Monoclonal antibodies were prepared using hybridoma technology, and screened for catalysis of the ring‐opening isomerization and/or decarboxylation of a series of related benzisoxazoles and their 3‐carboxy‐derivatives. No catalysis of decarboxylation was observed, but4of a total of 47 antibodies obtained against the three haptens catalyzed the isomerization process. Of 12 antibodies raised against the 3‐acetylbenzisoxazole structure5none was catalytically active; but one of 24 raised against a 3‐isopropenylbenzisoxazole6increased the rate of ring‐opening of 6‐nitrobenzisoxazole, and 5 of 11 antibodies raised against a benzisoxazole7with a 3‐amidinium group were moderately active against either 6‐nitro or 6‐acylaminobenzisoxazoles. Competitive binding studies suggest that at least some of the antibodies induced by the isopropenyl hapten do possess a recognizably hydro

ISSN:0021-2148    

DOI:10.1002/ijch.199600024

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe relevance of antibody catalysis to synthetic organic chemistry is demonstrated here by an efficient total synthesis of (–)‐α‐multistriatin, the aggregation pheromone of the European elm bark beetle,Scolytus multistriatus, which is the principal vector of the Dutch elm disease, responsible for the severe devastation of the elm population in Europe and North America. The key step in our synthesis of this natural product is an antibody‐catalyzed, enantioselective protonolysis of an enol ether to produce a branched ketone. The latter is obtained with an (S) configuration in greater than 99% enantiomeric excess. Catalysis follows Michaelis‐Menten kinetics (Km= 230 μM,kcat= 0.36 min−1) and useful rate enhancement (kcat/kun= 65,000 at pH 6.5). This abzymic step is followed by twelve chemical steps, with all four asymmetric centers originating from the chirality achieved in the antibody‐catalyzed reaction. That specific step is a unique example of a chemical transformation which is difficult to achieve either by an available synthetic methodology or via catalysis with a known enzyme. The synthetic pheromone has been checked in field experiments and found as active as the naturally occurring compound in attracting the European e

ISSN:0021-2148    

DOI:10.1002/ijch.199600025

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe antibody phage display system has been investigated as a vehicle for the potential altering of a catalytic antibody's specificity and chemical reactivity. Using previously identified catalytic antibodies, heavy and light “chain shuffling” experiments have been conducted. Catalytic activity and specificity requirements in terms of antibody complementarity‐determining regions were probed by interchanging heavy and light chain genes between antibodies that catalyze class‐similar but different chemical reactions with substrates that are enantiomerically opposed. The results were that antibody‐hapten binding specificity was only slightly altered, but catalytic activity was severely co

ISSN:0021-2148    

DOI:10.1002/ijch.199600026

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY