20 amino acids

Deceptive---packing is critical

Solution crystal structure of the prion monomer

…to Discovery Studio

monomer Dimer (domain swapped)

Expression and crystallization.Human prion protein (90–231)was expressed in E. coli, refolded and purified as described.Crystals, obtained at 20 °C by vapor diffusion with protein at 5 mg/ml and reservoir consisting of 0.1 M Tris-HCl, pH 8, 3 M NaCl and 5 mM CdCl2, were stabilized with 2,4-dimethyl-2,4-pentanediol prior to data collection at –180 °C.

Energy and Stability

A B

If A is favored over B then A is at lower energy…how much lower?

=

RT is thermal energy…the temperature converted into energy units by “R”

=

RT is thermal energy…the temperature converted into energy units by “R”

Our body temperature: 37C or 310 Kelvin or 2600 Joules

=

RT is thermal energy…the temperature converted into energy units by “R”

Our body temperature: 37C or 310 Kelvin or 2600 Joules

If the energy difference is zero, =1 so both are in equal amounts…at equilibriumIf the energy difference is 2600 Joules then B is 2.7 times greater than A

=

RT is thermal energy…the temperature converted into energy units by “R”

Our body temperature: 37C or 310 Kelvin or 2600 Joules/mole

If the energy difference is zero, =1 so both are in equal amounts… at equilibriumIf the energy difference is 2600 J/mole then B is 2.7 times greater than AIf the energy difference is 10 times 2600 J/mole then B is 20,000 times greater than A

=

RT is thermal energy…the temperature converted into energy units by “R”

Our body temperature: 37C or 310 Kelvin or 2600 Joules

If the energy difference is zero, =1 so both are in equal amounts… at equilibriumIf the energy difference is 2600 Joules then B is 2.7 times greater than AIf the energy difference is 10 times 2600 Joules then B is 20,000 times greater than A

If the energy difference is very big then it seems that all of A goes to B

How big is 2600 Joules/mole? …2.6 kJ/moleThe heat needed to melt water molecules: 6 kJ/moleTo break a hydrogen bond: 18-24 kJ/mole

Events happen spontaneously when energy needed is “close” to thermal energy

Energy barrier:

Events happen spontaneously when energy needed is “close” to thermal energy

Energy barrier:

A BC

EnergyA

C

BEnergy change

Energy to get change

Activation energy

For a rate of 1 in 109 sec: energy of 132kJ/moleFor probability of 1 in a million: energy=166kJ/mole

catalyzed catalyzed plus bound changes energy

uncatalyzed

Different species…must be stable for multiple animal lifetimesThus very low energy states…deep wells or high energy barriers

…protein must pack very well (low energy) in many different forms or transition structures are highly unstable