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CS31: In situ equilibria Tubulin and microtubules

NTP metabolism and transduction. CS31: In situ equilibria Tubulin and microtubules. Biochemistry 655 28 March 2011. Goals. Introduce the unit on free energy transformations: transduction Distinguish irreversible reactions from slow reactions.

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CS31: In situ equilibria Tubulin and microtubules

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  1. NTP metabolism and transduction CS31: In situ equilibriaTubulin and microtubules Biochemistry 655 28 March 2011

  2. Goals • Introduce the unit on free energy transformations: transduction • Distinguish irreversible reactions from slow reactions. • NTP hydrolysis in aqueous solution is irreversible and slow! • Discuss the water’s contribution to the overall DG of hydrolysis. • Compare the DG of GTP hydrolysis in water with that inside tubulin. • Discuss the meaning of “energy storage”. • Discuss the consequences of the conformational energy stored by tubulin when microtubules are assembled.

  3. Transduction transduce (tr":ns£dju:s, trÊns-, -nz-), v. [Back-formation from next.] 1. trans. To alter the physical nature or medium of (a signal); to convert variations in (a medium) into corresponding variations in another medium.

  4. ATP + H2O ADP + Pi … Becomes reversible inside a protein that can absorb the explosion... ATP + H2O ADP + Pi NTP hydrolysis fuels everything in the cell! A reaction that is explosivelyirreversible in water… …by changing shape, which stores free energy. These shape-changes drive all cellular processes!

  5. DG = 0 For a complete cycle Binding Equilibria Thermodynamic cycles with a transient ligand Conformational Equilibria

  6. NTP metabolism and transduction Cs32: Product release and free energy coupling Biochemistry 655 8 November 2009

  7. Goals • Review the principles of pre-steady state kinetics

  8. The Actomyosin cross-bridge cycle Actin pries myosin open, liberating ADP Myosin:ADP develops high affinity for Actin ATP binding drives AM apart Dissociated Myosin hydrolyzes ATP

  9. t1/2=50ms

  10. Steady-state ~100/s Transient phase 20/s 0.1/s

  11. DG = 0 For a complete cycle Binding Equilibria A thermodynamic cycle Conformational Equilibria

  12. Activated Closed, pre-transition state complex Products: NDP, Pi 3-State behavior and ATP utilization P-O-P Bond Hydrolysis Chemical transformation of nucleotide NTP binding Nucleotide exchange Induced fit Catalysis Turnover OPEN: Ligand-free High affinity for NTP Movement, enzyme activation, assembly Product (NDP, Pi) release

  13. Actin conformational changes

  14. Internal rigid body mechanics of Actin

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