MODULATION OF ENZYME-ACTIVITY BY ANTIBODY-BINDING TO AN ALKALINE-PHOSPHATASE - EPITOPE HYBRID PROTEIN

An epitope from the HIV-1 gp120 protein V3 loop has been inserted onto the surface of bacterial alkaline phosphatase at different positions in the vicinity of the enzyme active site, creating hybrid proteins th at can bind to an anti-gp120 monoclonal antibody. One of the hybrid pr oteins, API1, has a 13 amino acid V3 loop sequence inserted between re sidues 407 and 408 of alkaline phosphatase. The enzymatic activity of this protein is modulated upon antibody binding. API1 maintains the fu ll activity of the wild type alkaline phosphatase but in the presence of the anti-gp120 antibody, the enzyme activity is inhibited by 40-50% . Thus, the hybrid enzyme can be used to detect the presence of antibo dy in solution. The concept of signalling proteins may have a wide app lication. Two models for the mechanism of modulation, steric hindrance and allosteric regulation, are discussed.