Regulation through Covalent Modification

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Regulation through Covalent Modification
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Phosphorylation

• Serine, Threonine and Tyrosine residues
• Phosphorylation and de-phosphorylation
• Kinases, use ATP to add P to protein
• Phosphatases, remove P from protein

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Phosphorylation
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Human has 518 protein kinases There are 45,000
PKL.
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Protein Phosphatase
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Energy in ATP Drives the both Reactions
Kinase
Phosphatase
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Advantages of Using PO32-

• Adding two negative charges
• Forming three or more H-bonds
• Creating a great equilibrium constant of
  different protein conformations (?Go -12
  kcal/mol)
• Fast kinetics

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Protein Kinase A

• MW 160 kd
• 4 subunits
• 2 regulatory subunits
• 2 catalytic subunits
• Specificity
• -R-R-G-S-I- -R-R-G-S-I-

P
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Catalytic activity of PKA is inhibited by a
pseudosubstrate sequence in R-subunits
Substrate -R-R-G-S-I- Inhibitor -R-R-G-A-I-
Ribbon model
Space-filled model
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Activation of Protein Kinase A by cAMP
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Protein Kinase A (PKA) is Activated by cAMP
Adenyl cyclase
ATP
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Insulin, glucagon
Phosphodiesterase
AC
ATP
cAMP
AMP
PKA (active)
PKA (inactive)
Pyruvate dehydrogenase acetyl-CoA carboxylase
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GTP
Guanylyl cyclase
cGMP
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