PROTEIN PHYSICSPROTEIN PHYSICS

LECTURES 11-12LECTURES 11-12

- Fibrous proteins and their functions- Fibrous proteins and their functions- Membrane proteins and their functions - Membrane proteins and their functions

Globular proteinsGlobular proteins

Fibrous proteinsFibrous proteins

H-bonds (NH:::OC)H-bonds (NH:::OC) & & hydrophobic forceshydrophobic forces

MembraneMembraneproteinsproteins

Fibrous proteinsFibrous proteins: regular building blocks: regular building blocks

________________________________________________________________________HereHere, we do not consider fibrous proteins , we do not consider fibrous proteins made from globules (actin, etc.)made from globules (actin, etc.)

collagencollagen

Fibrous proteinsFibrous proteins: regular building blocks: regular building blocks

collagencollagen

Silk fibroinSilk fibroin ~50~50

4.8A4.8A

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__________

-helical-helicalcoiled-coiled-coilcoil

-helix packing-helix packing

collagencollagen triple helix: triple helix: 3 chains 3 chains [Gly-X- [Gly-X-

Pro]Pro]500500

PRO (PRO ( = -70 = -70oo))

Before PROBefore PRO

PolyPRO IIPolyPRO II

PolyPRO IIPolyPRO II

Collagen: Collagen: assisted assisted foldingfolding

Elastin:Elastin:

Matrix protein. Matrix protein. Short repeats. Short repeats. Poor secondary structure.Poor secondary structure.Chains are linked by chemically Chains are linked by chemically modified modified LysLys residues. residues.Like in rubber. Like in rubber.

Natively non-structured fibrous Natively non-structured fibrous proteins:proteins:

H-bondsH-bonds & & hydrophobicshydrophobics

Membrane proteinsMembrane proteins: transmitters: transmitters

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heads (polar)tailstailsheads (polar)

BacteriorodopsinBacteriorodopsinwith retinalwith retinal

Transport of protons HTransport of protons H++

HH++

HH++

PorinPorinTransport of polar moleculesTransport of polar molecules

Pore in membrane: SELECTIVITYPore in membrane: SELECTIVITY

Free energy of a charge in the non-charged non-polar pore:Free energy of a charge in the non-charged non-polar pore:

~ q~ q2 2 // [( [(MEMBRMEMBR WATERWATER ) )1/21/2 rrPOREPORE] ~ ] ~

~ 20 kcal/mol ~ 20 kcal/mol / / rrPOREPORE((ÅÅ))

+

Photo-Photo-syntheticsyntheticcentercenter

PigmentsPigmentsin photo-in photo-syntheticsyntheticcenter:center:ElectronElectrontransfertransfer

chlorophyllchlorophyll

LightLight

TunnelingTunneling

P(X) ~ 10P(X) ~ 10-X(-X(Å)Å)

T-independentT-independentFrequency of Frequency of vibrations (attacks):vibrations (attacks):f ~ 10f ~ 101515/sec/secSuccessful attacks:Successful attacks:ffSUCCSSUCCS..(x)(x) ~ P(x)•f~ P(x)•f,, e.g.: e.g.:

ffSUCCSSUCCS..(5Å)(5Å) ~ 10~ 10-5+15 -5+15 ~ ~

~ 10~ 101010/sec/sec

Atom Atom 1 1Å Å Attenuation of Attenuation of electron density: electron density:

- Fibrous proteins: building blocks- Fibrous proteins: building blocks- Membrane proteins: transmitters- Membrane proteins: transmitters