A MOLECULAR SENSOR SYSTEM BASED ON GENETICALLY-ENGINEERED ALKALINE-PHOSPHATASE

Binding and signaling proteins based on Escherichia coli alkaline phos phatase (AP; EC 3.1.3.1) were designed for the detection of antibodies , Hybrid proteins were constructed by using wild-type AP and point mut ants of AP [Asp-101 --> Ser (D101S) and Asp-153 --> Gly (D153G)]. The binding function of the hybrid proteins is provided by a peptide epito pe inserted between amino acids 407 and 408 in AP. Binding of anti-epi tope antibodies to the hybrid proteins modulates the enzyme activity o f the hybrids; upon antibody binding, enzyme activity can increase to as much as 300% of the level of activity in the absence of antibody or can decrease as much as 40%, depending on the presence or absence of the point mutations in AP, The fact that modulation is altered from in hibition to activation by single amino acid changes in the active site of AP suggests that the mechanism for modulation is due to structural alterations upon antibody binding, Modulation is a general phenomenon , The properties of the system are demonstrated by using two epitopes, one from the V3 loop of human immuuodeficiency virus type 1 gp120 pro tein and one from hepatitis C virus core protein, and corresponding mo noclonal antibodies, The trend of modulation is consistent for all hyb rids; those in wild-type AP are inhibited by antibody, while those in the AP mutants are activated by antibody, This demonstrates that modul ation of enzyme activity of the AP-epitope hybrid proteins is not spec ific to either a particular epitope sequence or a particular antibody- epitope combination,