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Human phosphatidylinositol 4-kinase isoform PI4K92. Expression of the recombinant enzyme and determination of
S Suer1, A Sickmann, H E Meyer
1Institut für Physiol. Chem., Abt. für Biochemie Systeme und Proteinstrukturlabor, Ruhr-Universität Bochum, Germany.
Abstract:
Human phosphatidylinositol 4-kinase, isoform PI4K92, was expressed as His6 tagged protein in Sf9 cells reaching a level of approximately 5% of cellular protein. The enzyme can be purified nearly to homogeneity in a single step by absorption/desorption on Ni/nitriloacetic acid agarose magnetic beads. High Km values in the millimolar range for ATP and PtdIns as well as only a moderate inhibition by adenosine and a sensitivity to Wortmannin (IC50 approximately 300 nM) characterize the enzyme as a type 3 PI4K. The enzyme produces PtdIns4P as product. The isolated enzyme is a phosphoprotein, additionally phosphate is incorporated by incubation with ATP/Mg or ATP/Mn. Phosphorylation sites were mapped by MALDI-MS and LC-MS/MS at the following positions: S258, T263, S266, S277, S294, T423, S496, T504. Accordingly, a stretch of 81 amino acids between the common and the C-terminal catalytic domain was designated phosphorylation domain.
Insights
This study characterizes human phosphatidylinositol 4-kinase, isoform PI4K92, a type 3 PI4K. The enzyme produces phosphatidylinositol 4-phosphate (PtdIns4P) and is regulated by phosphorylation.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Phosphatidylinositol 4-kinases (PI4Ks) are crucial enzymes involved in lipid signaling pathways.
- Understanding the specific isoforms, like PI4K92, is essential for elucidating their distinct cellular functions.
Purpose of the Study:
- To express, purify, and characterize human phosphatidylinositol 4-kinase, isoform PI4K92.
- To determine the enzymatic properties and phosphorylation status of PI4K92.
Main Methods:
- Expression of His6-tagged PI4K92 in Sf9 insect cells.
- Single-step purification using Ni/nitrilotriacetic acid agarose magnetic beads.
- Enzymatic assays to determine kinetic parameters (Km) and inhibition profiles (adenosine, Wortmannin).
- Mass spectrometry (MALDI-MS, LC-MS/MS) for mapping phosphorylation sites.
Main Results:
- PI4K92 was expressed at high levels and purified to near homogeneity.
- The enzyme exhibited high Km values for ATP and PtdIns, moderate inhibition by adenosine, and sensitivity to Wortmannin, consistent with a type 3 PI4K.
- PI4K92 produces phosphatidylinositol 4-phosphate (PtdIns4P).
- The purified enzyme is a phosphoprotein, with phosphorylation sites identified within a specific domain (S258, T263, S266, S277, S294, T423, S496, T504).
Conclusions:
- Human PI4K92 is a type 3 phosphatidylinositol 4-kinase with specific kinetic and inhibition properties.
- PI4K92 is a phosphoprotein, and its phosphorylation sites are located in a distinct domain, suggesting regulatory roles.
- This characterization provides a foundation for further investigation into PI4K92's biological functions and therapeutic potential.