A conformational transition between an open and closed form of human pancreatic lipase revealed by a monoclonal antibody

The interfacial activation of human pancreatic lipase (HPL) probably involv es the motion of a lid covering the active site of the enzyme. Here we obse rved that the presence of either bile salts or a small proportion of water- miscible organic solvents (called activator compounds) considerably enhance s the enzymatic activity of HPL on a monomeric solution of tripropionin. Th is finding suggests that the activator compounds may favor the opening of t he lid. This hypothesis was checked by comparing the immunoreactivity of HP L and HPL with a mini-lid (HPL(-lid)) towards anti-HPL monoclonal antibodie s (mAbs), in the presence and absence of the activator compounds. A single conformational mAb (248-31) fails to immunoprecipitate HPL in the presence of activator compounds and HPL covalently inhibited with diethyl p-nitrophe nyl phosphate (DP.HPL). This loss of recognition of HPL by mAb 248-31 was p robably due to the motion of the lid, since HPL(-lid) was always recognized in the presence or absence of activator compounds. Furthermore, two other mAbs (81-23 and 146-40) immunoprecipitated HPL similarly whether or not the activator compounds were present. MAb 248-31 therefore specifically recogn izes HPL in the closed but not the open conformation. (C) 2000 Elsevier Sci ence B.V. All rights reserved.