ANTI-HIV PROTEINASE MONOCLONAL ANTIBODY F11.2.32 THAT INHIBITS ENZYME ACTIVITY

Renata Štouracova¹, Julien Lescar², Jiri Brynda¹, Marie-Madelaine Riottot², Véronique Chitarra², Milan Fabry¹, Magda Horejsi¹, Pavlína Rezacova¹, Graham Bentley² and Juraj Sedlacek¹

¹Department of Gene Manipulation, Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 166 42 Prague, Czech Republic
²Unité d´Immunologie Structurale, Institut Pasteur , Paris, France

F11.2.32 a monoclonal antibody raised against HIV1 protease (K_d= 5nM) which inhibits proteolytic activity of the enzyme (K_inh=35(+3)Nm), has been studied by crystallographic methods. F11.2.32 mAb has been found to be reactive to peptide MSLPGRWKPKM (positions 36-46) of HIV1 protease. The F11.2.32 epitope relates to flap region of the enzyme.The three-dimensional structure of the complex between the Fab fragment and a synthetic peptide, spaning residues 36 to 46 of the protease, has been determined at 2.2 A resolution, and that of the Fab in the free state has been determined at 2.6A resolution. The rafined model of the complex reveals ten well-ordered residues of the peptide (P36-P45) bound in a hydrophobic cavity at the centre of the antigen binding site. An intermolecular antiparallel -sheet is formed between the peptide and CDR3-H loop of the antibody, additional polar interactions occur between main chain atoms of the peptide and hydroxyl groups from tyrosine residues protruding from CDR1-L and CDR3-H. The conformation of the bound peptide, which shows no overall structural similarity to the corresponding segment in HIV1 protease, suggests that F11.2.32 might inhibit proteolysis by distorting the native structure of the enzyme.

The tested antibody is meant to serve as lead compound for constructing alternative non-active sit inhibitors of lower molecular weight.