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Crystal structure of an inactive Akt2 kinase domain
Xin Huang1, Michael Begley, Kurt A Morgenstern
1Amgen Cambridge Research Center, One Kendall Square, Building 1000, Cambridge, MA 02139, USA. hxin@amgen.com
Abstract:
Akt/PKB represents a subfamily of three isoforms from the AGC serine/threonine kinase family. Amplification of Akt activity has been implicated in diseases that involve inappropriate cell survival, including a number of human malignancies. The structure of an inactive and unliganded Akt2 kinase domain reveals several features that distinguish it from other kinases. Most of the alpha helix C is disordered. The activation loop in this structure adopts a conformation that appears to sterically hinder the binding of both ATP and peptide substrate. In addition, an intramolecular disulfide bond is observed between two cysteines in the activation loop. Residues within the linker region between the N- and C-terminal lobes also contribute to the inactive conformation by partially occupying the ATP binding site.
Insights
The Akt2 kinase structure reveals unique features, including a disordered alpha helix C and an activation loop that blocks ATP and substrate binding, explaining its inactive state. This structural insight is crucial for understanding cancer cell survival and developing targeted therapies.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Oncology
Background:
- The Akt/Protein Kinase B (PKB) family, comprising three serine/threonine kinase isoforms, plays a critical role in cell survival pathways.
- Dysregulated Akt activity is frequently observed in human malignancies, contributing to uncontrolled cell proliferation and disease progression.
Purpose of the Study:
- To elucidate the structural basis of Akt2 kinase inactivity.
- To identify key structural features that regulate Akt2 enzymatic activity for potential therapeutic targeting in cancer.
Main Methods:
- X-ray crystallography was employed to determine the three-dimensional structure of the inactive, unliganded Akt2 kinase domain.
- Structural analysis focused on identifying unique conformations and intramolecular interactions responsible for the kinase's quiescent state.
Main Results:
- The determined Akt2 structure exhibits a disordered alpha helix C, deviating from typical kinase conformations.
- The activation loop adopts a sterically hindering conformation, impeding ATP and peptide substrate binding.
- An intramolecular disulfide bond within the activation loop and linker region residues occupying the ATP-binding site further stabilize the inactive state.
Conclusions:
- The Akt2 kinase domain possesses intrinsic structural mechanisms that maintain an inactive conformation.
- These unique structural features, including the activation loop's conformation and disulfide bond, are critical determinants of Akt2 regulation.
- Understanding these structural elements provides a foundation for designing specific inhibitors to target aberrant Akt signaling in cancer.