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 AB 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”

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

RT is thermal energy…the temperature converted into energy units by “R” Our body temperature: 37C or 310 Kelvin or 2600 Joules/mole

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 very big then it seems that all of A goes to B

How big is 2600 Joules/mole? …2.6 kJ/mole The heat needed to melt water molecules: 6 kJ/mole To break a hydrogen bond: 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: ABC Energy A C B Energy change Energy to get change Activation energy For a rate of 1 in 10 9 sec: energy of 132kJ/mole For probability of 1 in a million: energy=166kJ/mole

catalyzedcatalyzed plus bound changes energy uncatalyzed

Different species …must be stable for multiple animal lifetimes Thus 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