8p0i
Crystal structure of the open conformation of insulin-regulated aminopeptidase in complex with a small-MW inhibitor
Structural highlights
FunctionLCAP_HUMAN Release of an N-terminal amino acid, cleaves before cysteine, leucine as well as other amino acids. Degrades peptide hormones such as oxytocin, vasopressin and angiotensin III, and plays a role in maintaining homeostasis during pregnancy. May be involved in the inactivation of neuronal peptides in the brain. Cleaves Met-enkephalin and dynorphin. Binds angiotensin IV and may be the angiotensin IV receptor in the brain.[1] [2] [3] Publication Abstract from PubMedInsulin-regulated aminopeptidase (IRAP) is an enzyme with important biological functions and the target of drug-discovery efforts. We combined in silico screening with a medicinal chemistry optimization campaign to discover a nanomolar inhibitor of IRAP based on a pyrazolylpyrimidine scaffold. This compound displays an excellent selectivity profile versus homologous aminopeptidases, and kinetic analysis suggests it utilizes an uncompetitive mechanism of action when inhibiting the cleavage of a typical dipeptidic substrate. Surprisingly, the compound is a poor inhibitor of the processing of the physiological cyclic peptide substrate oxytocin and a 10mer antigenic epitope precursor but displays a biphasic inhibition profile for the trimming of a 9mer antigenic peptide. While the compound reduces IRAP-dependent cross-presentation of an 8mer epitope in a cellular assay, it fails to block in vitro trimming of select epitope precursors. To gain insight into the mechanism and basis of this unusual selectivity for this inhibitor, we solved the crystal structure of its complex with IRAP. The structure indicated direct zinc(II) engagement by the pyrazolylpyrimidine scaffold and revealed that the compound binds to an open conformation of the enzyme in a pose that should block the conformational transition to the enzymatically active closed conformation previously observed for other low-molecular-weight inhibitors. This compound constitutes the first IRAP inhibitor targeting the active site that utilizes a conformation-specific mechanism of action, provides insight into the intricacies of the IRAP catalytic cycle, and highlights a novel approach to regulating IRAP activity by blocking its conformational rearrangements. Stabilization of the open conformation omicronf insulin-regulated aminopeptidase by a novel substrate-selective small-molecule inhibitor.,Mpakali A, Georgaki G, Buson A, Findlay AD, Foot JS, Mauvais FX, van Endert P, Giastas P, Hamprecht DW, Stratikos E Protein Sci. 2024 Sep;33(9):e5151. doi: 10.1002/pro.5151. PMID:39167040[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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