Related Experiment Videos
Properties of a microtubule-associated cofactor-independent protein kinase from pig brain
C W Scott1, C B Caputo, A I Salama
1Department of Pharmacology, ICI Americas, Wilmington, DE 19897.
Abstract:
A protein kinase activity was identified in pig brain that co-purified with microtubules through repeated cycles of temperature-dependent assembly and disassembly. The microtubule-associated protein kinase (MTAK) phosphorylated histone H1; this activity was not stimulated by cyclic nucleotides. Ca2+ plus calmodulin, phospholipids or polyamines. MTAK did not phosphorylate synthetic peptides which are substrates for cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase. Ca2+/calmodulin-dependent protein kinase II, protein kinase C or casein kinase II. MTAK activity was inhibited by trifluoperazine [IC50 (median inhibitory concn.) = 600 microM] in a Ca2+-independent fashion. Ca2+ alone was inhibitory [IC50 = 4 mM). MTAK was not inhibited by heparin, a potent inhibitor of casein kinase II, nor a synthetic peptide inhibitor of cyclic AMP-dependent protein kinase. MTAK demonstrated a broad pH maximum (7.5-8.5) and an apparent Km for ATP of 45 microM. Mg2+ was required for enzyme activity and could not be replaced by Mn2+. MTAK phosphorylated serine and threonine residues on histone H1. MTAK is a unique cofactor-independent protein kinase that binds to microtubule structures.
Insights
Researchers discovered a novel microtubule-associated protein kinase (MTAK) in pig brains. This unique enzyme phosphorylates histone H1 independently of cofactors and binds to microtubules.
Area of Science:
- Neurochemistry
- Molecular Biology
- Enzymology
Background:
- Microtubules are crucial cytoskeletal components involved in various cellular processes.
- Protein kinases play vital roles in cell signaling and regulation.
- Identifying novel kinases associated with microtubules can elucidate their regulatory mechanisms.
Purpose of the Study:
- To identify and characterize novel protein kinase activities associated with pig brain microtubules.
- To determine the substrate specificity and regulatory properties of the identified kinase.
- To investigate the relationship between the kinase and microtubule structures.
Main Methods:
- Co-purification of kinase activity with microtubules through assembly/disassembly cycles.
- Histone H1 phosphorylation assays.
- Testing substrate specificity against various known kinase peptide substrates.
- Inhibition studies using specific kinase inhibitors and ions.
- Enzyme kinetic analysis (pH optimum, Km for ATP, metal ion requirement).
Main Results:
- A protein kinase activity, termed microtubule-associated protein kinase (MTAK), was co-purified with pig brain microtubules.
- MTAK phosphorylated histone H1, primarily at serine and threonine residues.
- MTAK activity was not stimulated by cyclic nucleotides, Ca2+/calmodulin, phospholipids, or polyamines.
- MTAK showed unique substrate specificity, not phosphorylating known substrates of other major kinase families.
- The enzyme was inhibited by trifluoperazine and Ca2+ in a Ca2+-independent manner.
- MTAK demonstrated optimal activity at pH 7.5-8.5, required Mg2+, and had an apparent Km for ATP of 45 μM.
- MTAK is a cofactor-independent kinase that binds to microtubules.
Conclusions:
- A novel cofactor-independent protein kinase (MTAK) associated with microtubules has been identified in pig brain.
- MTAK exhibits unique substrate specificity and regulatory properties, distinct from known protein kinases.
- The findings suggest MTAK plays a specific role in microtubule-associated functions, potentially through histone H1 phosphorylation.