Cyclin Dependent protein kinases and the cell cycle (L13) Flashcards
How are CDKs activated?
By complex formation with cyclin
How are CDKs made catalytically competent?
By phosphorylation by CDK activating kinase
What are CDKs composed of?
Heterodimers of a catalytic CDK and a cyclin molecule
What are the 4 major stage stages of the cell cycle?
- The S phase- Entire DNA duplicated and chromoomes doubled
- Gap G2
- M phase- mitosis
- Gap G1
Why are there halts in the cell cycle?
May allow damaged DNA to be corrected or may prevent its replication, or may initiate apoptosis is the cell is beyond repair
How are CDKs and the cell cycle related?
The activated CDKs are effectively a series of switches which govern the passage of the cell through the steps
Statutory CDK mediated halts and intervals in the cell cycle, and brakes on proliferation, only occurs if the relevant CDKs are inhibited
Successful phosphorylation of their target proteins by the CDKs gives reaction products which themselves are crucial to the controlled progression of the cell cycle
What is the primary target of the G1 CDK4/6-cycline D complex?
pRb
How are CDKs involved in cell cycle control?
Phosphorylation of pRB activates the E2F transcription factor family to transcribe the G1 to S checkpoint cyclin E and the S phase cyclin A.
The active CDK2-cyclin E complex sustains pRB phosphorylation (inactivation) and thus supports entry into the S phase and replication (inhib prolongs the G1 phase)
How does p53 and p21 limit the proliferation controlled by the G1 to S ans S phase complexes?
p21 and p27 are members of the cip/kip family of CKIs.
The INK family of inhibitors includes p16
p53 downregulates pRB, perhaps to sustain E2F activity following degradation of the G1 and G1/S CDK- cyclin complexes which inactivate pRb.
p53 also promotes apoptosis
What is p53 activated by?
MAP kinase
What effect will mutation or loss of Rb tumor suppressor gene have?
Uncontrolled transcription by E2F
What effect will mutation or loss of CDK2-cyclin E inhibition have?
Free pass through the G1-S checkpoint
What effect will mutation or loss of CDK2-cyclin A inhibition have?
Remove controlling restraints within the S phase
What is the structure of Cyclin A?
Two similar domains, each with 5 alpha helices. The domain is called the cyclin fold.
The N-terminal domain has an amino acid sequence that is strongly conserved in all cyclins= cyclin box
What is the structure of CDK2?
Folded into 2 domains
The N-terminal domain comprises a 5 starnded beta-sheet and an alpha-helix that has the PSTAIRE sequence
The PSTAIRE helix (C helix) highly conserved in all protein kinases with the E being Glu51.
C-term domain is mainly alpha helical and contains a flexible loop region called the T-loop or activation loop which includes Thr160 which is phosphorylated in the fully active enzyme