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Publication Abstract from PubMed

The trimeric serine protease HTRA1 is a genetic risk factor associated with geographic atrophy (GA), a currently untreatable form of age-related macular degeneration. Here, we describe the allosteric inhibition mechanism of HTRA1 by a clinical Fab fragment, currently being evaluated for GA treatment. Using cryo-EM, X-ray crystallography and biochemical assays we identify the exposed LoopA of HTRA1 as the sole Fab epitope, which is approximately 30 A away from the active site. The cryo-EM structure of the HTRA1:Fab complex in combination with molecular dynamics simulations revealed that Fab binding to LoopA locks HTRA1 in a non-competent conformational state, incapable of supporting catalysis. Moreover, grafting the HTRA1-LoopA epitope onto HTRA2 and HTRA3 transferred the allosteric inhibition mechanism. This suggests a conserved conformational lock mechanism across the HTRA family and a critical role of LoopA for catalysis, which was supported by the reduced activity of HTRA1-3 upon LoopA deletion or perturbation. This study reveals the long-range inhibition mechanism of the clinical Fab and identifies an essential function of the exposed LoopA for activity of HTRA family proteases.

Allosteric inhibition of HTRA1 activity by a conformational lock mechanism to treat age-related macular degeneration.,Gerhardy S, Ultsch M, Tang W, Green E, Holden JK, Li W, Estevez A, Arthur C, Tom I, Rohou A, Kirchhofer D Nat Commun. 2022 Sep 5;13(1):5222. doi: 10.1038/s41467-022-32760-9. PMID:36064790^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.