CRYSTAL STRUCTURE DETERMINATION OF CATALYTIC ANTIBODIES

点击翻译按钮获取中文摘要

DESCRIPTION: Structure-function studies of catalytic antibodies are to focus on three systems. (1) The antibody 48G7 which was elicited to a phosphonate transition-state (TS) analogue and catalyzes the hydrolysis of the corresponding esters and carbonates. This system represents one of the simplest and most prevalent antibody-catalyzed reactions to study transition state stabilization and catalysis. Moreover, the germline genes have been cloned and expressed, permitting the study of the immunological evolution of catalysis. The functional effects of affinity maturation on TS analogue binding and catalysis can be analyzed and interpreted in terms of the three-dimensional structures of both the mature (48G7) and germline antibodies. In addition, a high level expression system in E. coli will allow a systematic mutagenesis study of both the active site and somatically mutated residues. (2) The antibody AZ-28 which was elicited against a chairlike TS analogue and catalyzes the corresponding oxy-Cope rearrangement. There are virtually no enzymes that catalyze such pericyclic rearrangements with the exception of chorismate mutase, the mechanism of which remains unclear despite extensive structural and mechanistic studies. Consequently, detailed structure-function studies of this biological catalyst may shed insight into the requirements for catalysis of the chemical transformation. Moreover, the availability of a family of antibodies that catalyze this unimolecular reaction may help to elucidate those factors essential for activity. (3) The antibody 28B4.2 which catalyzes the oxygenation reaction of a thioether to the corresponding sulfoxide. This was the first biological catalyst to use an abiological "cofactor" for activity, i.e. a periodate ion, in place of the heme and flavin cofactors used by the corresponding enzymes. The kcat values for the antibody and enzymes are comparable, suggesting that this strategy may allow the replacement of expensive cofactors with inexpensive chemical cofactors. A detailed understanding of the structure and mechanism of this antibody and the relationship of the active site structure to hapten structure may suggest generalizations and may allow engineering of antibodies with enhanced stereoselectivities or may permit modification of the antibody to other reactions such as disulfide bond formation.