Fibrous Proteins
1o structure amino acid sequence
2o structure - helix
-sheet
H-bonding between
C=O- and N-H+ of backbone


some proteins only have 1o and 2o structure:
fibroin (silk)
keratin hair
collagen skin
-sheet
- helix
insoluble in H2O
non-polar residues
Tertiary structure
Primary structure
sequence of amino acids
Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly
Ala-Phe-Ser-Ser-Val- Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly-
Non-polar
Polar
Acidic or Basic
Alanine
Phenylalanine
Valine
Isoleusine
Methionine
Glycine
Serine
Histidine
Glutamic acid
Arginine
Aspartic acid
Asperagine
Tertiary structure
Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly
arrange these in an -helix
polar
exterior
7
His
3
Ser
11
4
Asp Ser
15
Gly
8
Ile
14 Asn
Val 12
10 Arg
Ala 1
Glu
6
Phe His Met
2
9
13
Val 5
non-polar
interior
Tertiary structure
interaction of the R-groups
+
-
-
-
+
+
-
hydrophobic residues
inside
globular proteins
proteins fold around
non-polar groups
polar and charged residues
outside
Tertiary structure
interactions of R-groups
1. Hydrophobic interactions
non-polar R-groups
LDF
2. Hydrogen bonding
polar R-groups
between H-bond
donors and acceptors
3. Ionic bonds (salt bridges) acidic and basic R-groups
ion-ion
4. Covalent bonds (disulfide)
cysteins
C-terminus
His
NH+
-O-CH Asp
O
Ala
CH3
His
Fe2+
=
Arg
Phe
Cys
S
S Cys
N-terminus
Pro
Pro
Quaternary Structure
hemoglobin
subunits
heme groups 4 - Fe
globin chains 2 -chains
2 - chains
held in position by interaction of R-groups
H
H3N
+
C
polar histidine inside - holds Fe2+
O
C
O
-
NH
N
pKa = 6.1
Denaturation
form is function
loss of native configuration denaturation
denaturation
peptide bonds not affected
H-bonds
disulfide bonds
ionic bonds
L.D.F.
disrupted
Denaturation
4o structure disrupted first subunits separate
3o structure disrupted
protein unfolds
2o structure disrupted
H-bonds broken
treatments are sometimes reversible renatured
sometimes irreversible
insulin
Denaturing treatments
1. Heat
above 50-60oC
2. pH
disrupt salt bridges
approach pHI
frying egg
sunburn
3. detergents unfold globular proteins SDS
-
+
-
-
+
Na+
SO4-
Denaturing treatments
4. reducing agents
oxidizing agents
5. Metal salts
S-S
Hg+, Pb+, Ag+
SH HS
S-Hg
O Hg+
C O
6. H-bonding solvents alcohol
acetone
7. “Chaotropes”
H2N
O
NH
C
C
urea
NH2
H2N
NH2
guanidine
Words of Wisdom
1. Heat sunburn
6. H-bonding solvents alcohol
3. detergents