Identification of a novel CaMKK substrate

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK) is known to activate downstream protein kinases like CaMKI, CaMKIV, and AMPK.
• Understanding the full scope of CaMKK-mediated signaling pathways is crucial for deciphering cellular responses.

Purpose of the Study:

• To identify novel substrates of CaMKK beyond known protein kinases.
• To explore new Ca(2+)-dependent signaling pathways regulated by CaMKK.

Main Methods:

• Utilized N(6)-(1-methylbutyl)-ATP and a genetically engineered CaMKKα mutant (CaMKKα (Phe(230)Gly)) to identify new substrates.
• Employed rat brain extracts and recombinant proteins for phosphorylation assays.
• Used LC-MS/MS for protein identification and confirmed phosphorylation sites in vitro and in cellulo.

Main Results:

• Identified Syndapin I as a novel 50kDa CaMKK substrate, phosphorylated at Thr(355) by CaMKKα and β isoforms.
• Demonstrated that CaMKK can phosphorylate a non-kinase protein, Syndapin I.
• Observed increased phosphorylation of Syndapin I in transfected HeLa cells upon co-expression of active CaMKK mutants.

Conclusions:

• CaMKK phosphorylates Syndapin I, a non-kinase substrate, expanding the known functions of CaMKK.
• This discovery suggests the existence of novel Ca(2+)-signaling pathways regulated by CaMKK that do not rely on downstream protein kinases.
• Provides a new avenue for research into Ca(2+)-mediated cellular regulation.