The active-site cysteine residue of Ca2+/calmodulin-dependent protein kinase I is protected from irreversible modification via generation of polysulfidation.

ABSTRACT

Ca2+/calmodulin (CaM)-dependent protein kinase (CaMK) I is activated by the phosphorylation of a crucial activation loop Thr177 by upstream kinases, CaMK kinase (CaMKK), and regulates axonal or dendritic extension and branching. Reactive sulfur species (RSS) modulate protein functions via polysulfidation of the reactive Cys residues. Here, we report that the activity of CaMKI was reversibly inhibited via its polysulfidation at Cys179 by RSS. In vitro incubation of CaMKI with the exogenous RSS donor Na2S3 resulted in a dose-dependent inhibition of the phosphorylation at Thr177 by CaMKK and inactivation of the enzymatic activity. Dithiothreitol (DTT), a small molecule reducing reagent, rescued these inhibitions. Conversely, mutated CaMKI (C179V) was resistant to the Na2S3-induced inactivation. In transfected cells expressing CaMKI, ionomycin-induced CaMKI activity was decreased upon treatment with Na2S4, whereas cells expressing mutant CaMKI (C179V) proved resistant to this treatment. A biotin-polyethylene glycol-conjugated maleimide capture assay revealed that CaMKI was a target for polysulfidation in cells. Furthermore, the polysulfidation of CaMKI protected Cys179 from its irreversible modification, known as protein succination. Thus, we propose that CaMKI was reversibly inhibited via polysulfidation of Cys179 by RSS, thereby protecting it from irreversible modification.