Mechanism of Fine-tuning pH Sensors in Proprotein Convertases: Identification of a pH-sensing Histidine Pair in the Propeptide of Proprotein Convertase 1/3 [Enzymology]

July 30th, 2015 by Williamson, D. M., Elferich, J., Shinde, U.

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, due to the observation that various PC paralogues are activated at different organellar pH. To ascertain additional determinants of PC activation, we analyze Proprotein Convertase 1/3 (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 while 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.
  • Posted in Journal of Biological Chemistry, Publications
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