Fibrous Protein Chart

Silk Fibroin

• Primary Sequence:

  • repetitive gly-ala or gly-ser motifs

• Secondary Structure:

  • extended antiparallel b sheets

• Stabilization Forces:

  • h-bonds between backbone and peptide groups

  • close packing of small side chains

• Tertiary/Quaternary Organization:

  • stacked b sheets alternating with amorphous regions → flexibility

• Mechanical Property:

  • strong yet flexible

  • resists breaking and doesnt stretch much

• Biological Role:

  • spider webs, silkworm cocoons → structural fibers

• Key Biochemical Notes:

  • small residues (gly, ala, ser) allow tight packing

  • b sheet stacking

Collagen

• Primary Sequence:

  • repeating tripeptide Gly - (Pro) - (Hyp)

• Secondary Structure:

  • LEFT handed helix (not a helix) coiled into RIGHT handed triple helix

• Stabilization Forces:

  • h-bonds involve glycine and hydroxyproline

  • covalent crosslinks between lysine/hydroxilysine

• Tertiary/Quaternary Organization:

  • three polypeptides wound around each other → collagen triple helix (assemble into fibrils)

• Mechanical Property:

  • very high tensile strength

  • resists stretching

• Biological Role:

  • connective tissue, tendons, cartilage, bone, skin

• Key Biochemical Notes:

  • requires vitamin C for hydroxylation of proline/lysine

  • scurvy results if deficient

a-Keratin

• Primary Sequence:

  • high in cysteine (for disulfides)

• Secondary Structure:

  • RIGHT handed a helices coiled into LEFT handed coiled coil

• Stabilization Forces:

  • disulfide bonds between cysteines; hydrophobic interactions

• Tertiary/Quaternary Organization:

  • 2 helices form coiled coil

  • further bundled into protofilaments and intermediate filaments

• Mechanical Property:

  • tough, flexible, degree of hardness varies with disulfide content

• Biological Role:

  • hair, wool, nails, claws, horns

• Key Biochemical Notes:

  • hard keratins are rich in disulfides

  • soft keratins fewer disulfides

Motifs

• 4 helix bundle that stabilize HGH (stabilized by disulfide bonds)

• TIM barrel (alternate a and b sheet connected by loops - most common)

Myoglobin vs. hemoglobin

Myoglobin

• 1 heme group

• high affinity

  • hyperbolic binding

• no quaternary

Hemoglobin

• 4 heme groups

• cooperative binding

  • sigmoidal

Both

• reversibly bind to O2

• Fe2+ containing heme

• globular fold and (8) a helices

• histidine

Proximity and orientation effect

enzyme brings substrate closer to other substrates or to active site and does this in the correct orientation that makes them more likely to react with each other with the right proximity and orientation increasing the likelikhood they will bind

Desolvation

substrate, usually in a cell surrounded by water, when it interacts with enzyme no longer surrounded by water. It is surrounded by active site instead meaning that water no longer stabilizes substrate and anything that might have reacted will react because it wont be stabilized by H2O.

Functional group alignment

residues in enzyme are close to react with the substrate

transition state stabilization

enzyme stabilizes transition state and lowers activation energy of that reaction.

describe how enzymes use strategic binding of the substrate to enhance catalytic activity

• proximity and orientation effect

• functional group alignment

• transition state stabilization

• desolvation