SignalingLectureFinal

Doing work to change the protein state a wonderful

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Doing work to change the protein state A wonderful and important topic for our consideration is that of posttranslational modifications. One of the tricks performed by the cytoplasmic side of a receptor (or its partners) is to do some posttranslational modification.
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phosphorylation In bio systems, changes in envir.conditions => the activity of an enzyme must be rapidly altered One of the most important regulatory modes in all of biology: regulation of protein activity by covalent attachment of phosphate groups The substrate for protein phosphorylation: target protein and ATP The enzyme: protein kinase (transfers the terminal phosphate group from ATP to a chemical group on a protein) A phosphate group carried 2 “-” charges => causes a dramatic change in the local charge distribution on the surface of the protein => drastic, large scale effect on protein structure and ability to bind This alteration is reversible: protein phosphatase
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The diversity of kinases “The whole molecular control network, leading from the receptors at the cell surface to the genes in the nucleus, can be viewed as a computing device; and, like that other computing device, the brain, it presents one of the hardest problems in biology.” Catalytic domains shown in green Roughly 250 aa long.
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phosphorylation: two internal state variables What is the fraction of activated proteins? How does it depend on the state of phosphorylation? Model: The “structural” state of the protein (active/inactive): σ s : σ s = 0 => inactive, σ s = 1 => active The state of phosphorylation of the protein: σ p : σ p = 0 => unphosphorylated, σ p = 1 => phosphorylated The state of phosphorylation can alter the relative energies of the active and inactive states => at equilibrium, most of the phosphorylated molecules will be in active form I 1 and I 2 are the electrostatic interaction energies btw the two charges in the active and inactive states
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phosphorylation: two internal state variables Using the σ variables, the free energy of the protein is which simplifies to => states&weights:
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phosphorylation: two internal state variables
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  • Fall '09
  • Binding energy, Adenosine triphosphate, Cooperativity, internal state variables

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