Protein structure Pt.2

Tertiary Structure

The overall spatial arrangement of atoms in a protein

• Stabilized by numerous weak interactions between amino acid side chains.

  -Largely hydrophobic and polar interactions

  -Can be stabilized by disulfide bonds

•Interacting amino acids are not necessarily next to each other in the primary sequence. 

Tertiary Structure: Two major classes

Fibrous and globular (water or lipid soluble)

a helix cross linked by disulfide bonds

tough, insoluble protective structures of varying hardness and flexibility

ex: hair, feathers, nails

B conformation collagen triple helix

high tensile strength w/out stretch

ex: silk fibroin, collagen of tendons, bone matrix

Collagen is an important constituent of •

•connective tissue: tendons, cartilage, bones, cornea of the eye

Structure of Collagen

Each collagen chain is a long Gly- and Pro-rich left-handed helix

• Three collagen chains intertwine into a right-handed superhelical triple helix

• The triple helix has higher tensile strength than a steel wire of equal cross section

• Many triple-helices assemble into a collagen fibril

4-Hydroxyproline in Collagen

• Forces the proline ring into a favorable pucker

• Offer more hydrogen bonds between the three strands of collagen 

• The post-translational processing is catalyzed by prolyl hydroxylase and requires α-ketoglutarate, molecular oxygen, and ascorbate (vitamin C)

Silk Fibroin

Fibroin is the main protein in silk from moths and spiders

• Antiparallel b sheet structure 

• Small side chains (Ala and Gly) allow the close packing of sheets

Structure is stabilized by

• hydrogen bonding within sheets

• London dispersion interactions between sheets

Spider Silk

Used for webs, egg sacks, and wrapping the prey

• Extremely strong material

• stronger than steel

• can stretch a lot before breaking

A composite material

• crystalline parts (fibroin-rich)

• rubber-like stretchy parts

Motifs (folds)

Specific arrangement of several secondary structure elements

• All alpha-helix

• All beta-sheet

• Both

Motifs can be found as reoccurring structures in numerous proteins

Proteins are made of different motifs folded together