title: Mechanism of Fine-tuning pH Sensors in Proprotein Convertases: IDENTIFICATION OF A pH-SENSING HISTIDINE PAIR IN THE PROPEPTIDE OF PROPROTEIN CONVERTASE 1/3.
abstract: The propeptides of proprotein convertases (PCs) regulate activation of cognate protease domains by sensing pH of their organellar compartments as they transit the secretory pathway. Earlier experimental work identified a conserved histidine-encoded pH sensor within the propeptide of the canonical PC, furin. To date, whether protonation of this conserved histidine is solely responsible for PC activation has remained unclear because of the observation that various PC paralogues are activated at different organellar pH values. To ascertain additional determinants of PC activation, we analyzed PC1/3, a paralogue of furin that is activated at a pH of ∼5.4. Using biophysical, biochemical, and cell-based methods, we mimicked the protonation status of various histidines within the propeptide of PC1/3 and examined how such alterations can modulate pH-dependent protease activation. Our results indicate that whereas the conserved histidine plays a crucial role in pH sensing and activation of this protease an additional histidine acts as a "gatekeeper" that fine-tunes the sensitivity of the PC1/3 propeptide to facilitate the release inhibition at higher proton concentrations when compared with furin. Coupled with earlier analyses that highlighted the enrichment of the amino acid histidine within propeptides of secreted eukaryotic proteases, our work elucidates how secreted proteases have evolved to exploit the pH of the secretory pathway by altering the spatial juxtaposition of titratable groups to regulate their activity in a spatiotemporal fashion.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
authors.forename: Danielle M
authors.initials: DM
authors.lastname: Williamson
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
authors.forename: Johannes
authors.initials: J
authors.lastname: Elferich
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 shindeu@ohsu.edu.
authors.forename: Ujwal
authors.initials: U
authors.lastname: Shinde
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D045664:Proprotein Convertase 1 / Q000737:chemistry*
chemical_list: D006639:Histidine; D045664:Proprotein Convertase 1
keywords: histidine; organelle; pH regulation; pH sensor; propeptide-mediated folding; proprotein convertase 1/3; protease activation; protease inhibitor; protein folding; serine protease