Akt Kinase Activation Mechanisms Revealed Using Protein Semisynthesis

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Signaling

Background:

• Akt is a key protein kinase regulating cell proliferation and metabolism.
• Akt activation is primarily linked to C-terminal phosphorylation.
• Existing models focus on intramolecular interactions for Akt activation.

Purpose of the Study:

• To elucidate the precise mechanisms of Akt activation by specific phosphorylation events.
• To investigate the structural and functional consequences of C-terminal phosphorylation on Akt1.
• To differentiate the roles of distinct phosphorylation sites in Akt signaling.

Main Methods:

• Expressed protein ligation for site-specific phosphorylation of Akt1.
• Biochemical assays to analyze enzyme activity.
• Crystallography to determine structural changes.
• Cellular assays to assess Akt function in vivo.

Main Results:

• pSer473-Akt activation results from an intramolecular interaction between the C-tail and the PH-kinase domain linker, releasing PH domain-mediated autoinhibition.
• Dual phosphorylation at Ser477/Thr479 activates Akt1 via a distinct allosteric mechanism involving the activation loop.
• This dual phosphorylation reduces PH domain autoinhibition and lowers PIP3 affinity.

Conclusions:

• Akt activation is controlled by distinct allosteric mechanisms dependent on specific phosphorylation patterns.
• These findings offer a new framework for understanding Akt regulation in cellular signaling.
• Differentially phosphorylated Akt forms may possess unique functional roles in cellular processes.