Cryo-EM structures of inhibitory antibodies complexed with arginase 1 provide insight into mechanism of action

Abstract

Human Arginase 1 (hArg1) is a metalloenzyme that catalyzes the hydrolysis of l-arginine to l-ornithine and urea, and modulates T-cell-mediated immune response. Arginase-targeted therapies have been pursued across several disease areas including immunology, oncology, nervous system dysfunction, and cardiovascular dysfunction and diseases. Currently, all published hArg1 inhibitors are small molecules usually less than 350 Da in size. Here we report the cryo-electron microscopy structures of potent and inhibitory anti-hArg antibodies bound to hArg1 which form distinct macromolecular complexes that are greater than 650 kDa. With local resolutions of 3.5 Å or better we unambiguously mapped epitopes and paratopes for all five antibodies and determined that the antibodies act through orthosteric and allosteric mechanisms. These hArg1:antibody complexes present an alternative mechanism to inhibit hArg1 activity and highlight the ability to utilize antibodies as probes in the discovery and development of peptide and small molecule inhibitors for enzymes in general.

Neutralization of NET-associated human ARG1 enhances cancer immunotherapy

“…Monoclonal antibodies (mAbs) excel in their ability to bind antigens with high specificity, but they lack the ability to access the narrow cleft and active pocket of enzymes, mainly because of their steric hindrance. Recently, Abs toward full-length hARG1 were characterized ( 47 ), highlighting that alternative mechanisms for ARG1 inhibition are suitable, effective, and need to be further investigated. In this study, we examined the molecular biology of ARG1 in human neutrophils, showing that NETs are enriched in CTSS-cleaved ARG1 forms that specifically contribute to immunosuppression, which is efficiently neutralized by specific mAbs with potential to be combined with immunotherapy treatments for the treatment of PDAC.…”