Dec, 2012
In vitro substrate phosphorylation by Ca²⁺/calmodulin-dependent protein kinase kinase using guanosine-5 '-triphosphate as a phosphate donor
BMC Biochemistry
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- Volume
- 13
- Number
- First page
- 27
- Last page
- Language
- English
- Publishing type
- Research paper (scientific journal)
- DOI
- 10.1186/1471-2091-13-27
- Publisher
- BIOMED CENTRAL LTD
Background: Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) phosphorylates and activates particular downstream protein kinases -including CaMKI, CaMKIV, and AMPK- to stimulate multiple Ca2+-signal transduction pathways. To identify previously unidentified CaMKK substrates, we used various nucleotides as phosphate donors to develop and characterize an in vitro phosphorylation assay for CaMKK.
Results: Here, we found that the recombinant CaMKK isoforms were capable of utilizing Mg-GTP as a phosphate donor to phosphorylate the Thr residue in the activation-loop of CaMKI alpha (Thr(177)) and of AMPK (Thr(172)) in vitro. Kinetic analysis indicated that the K-m values of CaMKK isoforms for GTP (400-500 mu M) were significantly higher than those for ATP (similar to 15 mu M), and a 2- to 4-fold decrease in V-max was observed with GTP. We also confirmed that an ATP competitive CaMKK inhibitor, STO-609, also competes with GTP to inhibit the activities of CaMKK isoforms. In addition, to detect enhanced CaMKI phosphorylation in brain extracts with Mg-GTP and recombinant CaMKKs, we found potential CaMKK substrates of similar to 45 kDa and similar to 35 kDa whose Ca2+/CaM-induced phosphorylation was inhibited by STO-609.
Conclusions: These results indicated that screens that use STO-609 as a CaMKK inhibitor and Mg-GTP as a CaMKK-dependent phosphate donor might be useful to identify previously unidentified downstream target substrates of CaMKK.
Results: Here, we found that the recombinant CaMKK isoforms were capable of utilizing Mg-GTP as a phosphate donor to phosphorylate the Thr residue in the activation-loop of CaMKI alpha (Thr(177)) and of AMPK (Thr(172)) in vitro. Kinetic analysis indicated that the K-m values of CaMKK isoforms for GTP (400-500 mu M) were significantly higher than those for ATP (similar to 15 mu M), and a 2- to 4-fold decrease in V-max was observed with GTP. We also confirmed that an ATP competitive CaMKK inhibitor, STO-609, also competes with GTP to inhibit the activities of CaMKK isoforms. In addition, to detect enhanced CaMKI phosphorylation in brain extracts with Mg-GTP and recombinant CaMKKs, we found potential CaMKK substrates of similar to 45 kDa and similar to 35 kDa whose Ca2+/CaM-induced phosphorylation was inhibited by STO-609.
Conclusions: These results indicated that screens that use STO-609 as a CaMKK inhibitor and Mg-GTP as a CaMKK-dependent phosphate donor might be useful to identify previously unidentified downstream target substrates of CaMKK.
- Link information
- ID information
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- DOI : 10.1186/1471-2091-13-27
- ISSN : 1471-2091
- Pubmed ID : 23216827
- Web of Science ID : WOS:000313258200001