Autoproteolysis of human erythrocyte calpain-1 proceeds in vitro at high [Ca2+], through the conversion of the 80kDa catalytic subunit to a 75kDa activated enzyme that requires lower [Ca2+] for catalysis. Importantly, here we detect a similar 75kDa calpain-1 form also in vivo, in human meningiomas. Although calpastatin is so far considered the specific inhibitor of calpains, we have previously identified in rat brain a calpastatin transcript truncated at the end of the L-domain (cast110, L-DOM), coding for a protein lacking the inhibitory units. Aim of this study was to characterize the possible biochemical role of the L-DOM during calpain-1 autoproteolysis in vitro, at high (100 µM) and low (5 µM) [Ca2+]. Here we demonstrate that the L-DOM binds the 80kDa proenzyme in the absence of Ca2+. Consequently, we have explored the ability of the 75 kDa activated protease to catalyze at 5 µM Ca2+ the intermolecular activation of native calpain-1 associated with the L-DOM. Notably, this [Ca2+] is too low to promote the autoproteolytic activation of calpain-1 but enough to support the catalysis of the 75kDa calpain. We show for the first time that the L-DOM preserves native calpain-1 from the degradation mediated by the 75kDa form. Taken together our data suggest that the free L-domain of calpastatin is a novel member of the calpain/calpastatin system endowed with a function alternative to calpain inhibition. For this reason, it will be crucial to define the intracellular relevance of the L-domain in controlling calpain activation/activity in physio-pathological conditions having altered Ca2+ homeostasis.
|Titolo:||Unexpected role of the L-domain of calpastatin during the autoproteolytic activation of human erythrocyte calpain.|
|Data di pubblicazione:||2018|
|Appare nelle tipologie:||01.01 - Articolo su rivista|
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|2018 De Tullio, R.ab_Unexpected-role-of-the-Ldomain-of-calpastatin-during-the-autoproteolytic-activation-of-human-erythrocyte-calpainArticle_2018.pdf||articolo pubblicato in versione .PDF||Versione editoriale||Open Access Visualizza/Apri|