The crystal structure of cyclin A

Area of Science:

• Structural biology
• Molecular biology
• Biochemistry

Background:

• Eukaryotic cell cycle progression relies on cyclin-dependent protein kinases (CDKs).
• CDK activity is modulated by cyclins, which dictate kinase activity, localization, and substrate specificity.
• All cyclins share a conserved cyclin box domain, essential for their function.

Purpose of the Study:

• To determine the crystal structure of a functional fragment of bovine cyclin A.
• To elucidate the structural basis of cyclin A function and its interactions.
• To identify key regions within cyclin A involved in CDK binding and transcriptional regulation.

Main Methods:

• X-ray crystallography was used to solve the crystal structure of a recombinant bovine cyclin A fragment (cyclin A-3) at 2.0 Å resolution.
• Biochemical and genetic analyses were employed to understand cyclin A structure-function relationships.
• Threading analysis was performed to compare the cyclin box fold with other proteins.

Main Results:

• The crystal structure revealed the cyclin box possesses a five-alpha helix, alpha-helical fold.
• A similar fold was identified in the C-terminal region of cyclin A, despite low sequence similarity.
• Analysis identified conserved residue clusters on cyclin A, with one linked to CDK2 binding and another suggesting further protein interactions.

Conclusions:

• Cyclin A does not undergo significant conformational changes upon binding to CDK2.
• The cyclin-box fold serves as a structural template for the cyclin family.
• The cyclin-box fold functions as a generalized adaptor molecule in transcriptional regulation.