PROTEIN STRUCTURE

From: Protein Data Bank PDB ID: 1B0EKalus, W., Zweckstetter, M., Renner, C., Sanchez, Y., Georgescu, J., Grol, M., Demuth, D., Schumacher, R., Dony, C., Lang, K., Holak, T. A.:

structure of the IGF-binding domain of the insulin-like growth factor-binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions. EMBO J 17 pp. 6558 (1998)

Protein Structure

FUNCTIONS

Diverse functions related to structureStructural components of cellsMotor proteinsEnzymesAntibodiesHormonesHemoglobin/myoglobinTransport proteins in blood

STRUCTURE

Amino acidsAmino group (NH2)Carboxyl group

(COOH)

AMINO ACIDS

20 amino acids make up protein

8 essential amino acids (must be eaten in diet)9 in infant (histidine)

PROTEIN STRUCTURE - BONDING

5 bonds or forces determine structurePeptide bondHydrogen bondDisulfide bond Ionic bondHydrophobic force

PEPTIDE BOND

Peptide bond joins amino acids

Bond at both ends Increases range of

possible proteins1.0 x 1026 peptides

can be formed from 20 amino acids

CONDENSATION REACTION

PRIMARY PROTEIN STRUCTURE

Linear sequence of amino acids forms primary structure (long chain of amino acids)

Sequence essential for proper physiological function

SICKLE CELL ANEMIA

Replacement of a

single glutamine

amino acid with

valine in one chain

of hemoglobin alters

the structure and

function of the

protein

SECONDARY PROTEIN STRUCTURE

Peptide chains fold into secondary structures to become more compact: - helix - pleated sheet

ALPHA HELIX

- PLEATED SHEET

BETA HELIX

TERTIARY PROTEIN STRUCTURE

Secondary structures fold and pack

together to form tertiary structureUsually globular shape

Tertiary structure stabilized by bonds

between R groups (i.e. sidechains)

AMINO ACID R-GROUPSAll amino acids contain a carboxyl group and an amino group. R-Groups distinguish between individual amino acids. R-Groups make them different from one another.

TERTIARY STRUCTURE - H BOND

Hydrogen bonds are weak electrical attractions between positively and negatively charged atoms of different molecules.

TERTIARY STRUCTURE - DISULFIDE BOND

Covalent bond between sulfur atoms on two cysteine amino acids

TERTIARY STRUCTURE - IONIC BOND

Ions on R groups form bridges through ionic bonds

Ionic bonds form from the exchange of electrons between atoms

Example: NaCl (table salt)

TERTIARY STRUCTURE - HYDROPHOBIC FORCES

Close attraction of non-

polar R groups in the chains

Very weak but collective

interactions over large

areas help stabilize the

protein structure

ALL BONDS SHOWN TOGETHER

QUATERNARY PROTEIN STRUCTURE The arrangement of many tertiary structures into one

large protein molecule

Not all proteins have or need a quaternary structure

Allows for changes in structure/function in response

to chemical stimuli