protein structure and function Flashcards
Examples of Silk Proteins
- Collagen
- Elastin
- Keratin
- Silk Fibroin
▪ insoluble, extracellular (found outside the cell)
Collagen
▪ very strong due to aldol crosslinks (covalent bond)
▪ found in all animals
Collagen
▪ most abundant in the human body
Collagen
▪ essential in all connective tissues e.g. cartilage, bone, tendons, ligaments, and skin
Collagen
▪ triple helical structure (tropocollagen) stabilized by
aldol crosslinks
▪primary structure of collagen
repeating tripeptide (Gly-X-Y) where X is usually Pro and Y is usually hydroxyproline
they also exhibit H-bonding because of hydroxyproline
Collagen
they are not α-helical; just helical
Collagen
– excessive collagen synthesis
Fibrosis
▪ overproduction of type 1 collagen in lungs reduces the lung’s ability to expand for air intake and interferes with normal breathing; scarring of lungs
Pulmonary fibrosis
▪ excessive deposition in liver leads to scar tissue formation due to overconsumption of alcohol; may lead to cirrhosis
Liver fibrosis
caused by insufficient collagen production where skin and tendons are weak and easily stretched producing loose joints and hyperextensive limbs
Ehler’s-Danlos (Rubberman syndrome)
▪ type 1 procollagen molecules fail partially or completely to assemble into triple helices and are therefore degraded.
▪ reduced amount of collagen leads to fragile bones; easily fractured
Osteogenesis Imperfecta (Brittle bone syndrome)
▪ found predominantly in walls of arteries, lungs, intestines, skins, etc.
Elastin
▪ structural proteins that gives elasticity to the body’s tissues and organs
Elastin
MW of elastin
72 kDA
AAs in elastin
Small nonpolar
A,V, L,G
▪WHY hydrophobic elastin molecules “slide and stretch” over one another
to maintain structural integrity and provide recoil
▪ elastin protein molecules are crosslinked by WHAT TYPE OF BONDS
covalent bonds
tough, fibrous, insoluble protein that makes up the skin, hair and nails
KERATIN
also found in claws, hooves, feathers and horns
KERATIN
human hair is __% cysteine;
14
the more disulfide bridges present, the _ curly
more
Soft Keratin –____disulfide bonds
Hard Keratin – ____disulfide bonds
soft - less
hard-more
- most abundant protein in vertebrates
- has 3 polypeptide chains wrapped around each other in a ropelike twist or triple helix
collagen
collagen fibers are both intra and intermolecularly linked by covalent bonds formed by reactions of ______ residues
lysine and histidine
side chains of collagen are on the __ of the triple-helical molecule
surface
in collagen, the AA which facilitates formation of the helical conformation of each alpha chain because it causes kinks
Proline
in collagen, the AA which fits into the restricted spaces where the 3 chains come together
Glycine
in collagen, the AA important in stabilizing the triple-helical structure because it maximizes interchain H-bond formation
Hydroxyproline
*In collagen, Every 3rd position must be occupied by _
glycine.
300 nm, 1.5 nm in diameter
- held together by H-bonds (involving Hyp/P)
- MW: 300, 000
- each strand has 800 AA residues
tropocollagen
- precursor: tropoelastin
- linear polypeptide with about 700 AA, primarily small and nonpolar (A, V, L, G)
- also rich in protein and lysine, but contains only little hydroxylysine and hydroxyproline
elastin
formed by 3 allysyl side chains + 1 unaltered lysyl side chain from the same or neighboring peptide
-produces elastin
desmosine cross-link
– group of specialized proteins that contain heme as a tightly bound prosthetic group
Hemeproteins
has 8 alpha-helical regions and no beta-pleated sheet regions
- 2 polar histidine residues are found in the interior (F8 and E7)
- proximal histidine (F8) binds directly to the iron of heme
- distal histidine (E7) does not directly interact with heme group, but helps stabilize binding of oxygen to the ferrous iron
myoglobin
prosthetic group of myoglobin
heme group
= complete destruction of tertiary structure
Primary structure determines tertiary structure.
Denaturation + reduction of disulfide bonds
- The 2 alpha chains and the 2 beta chains are identical.
- Many of the AA of alpha chain, beta chain and myoglobin are homologous (same AA in same position).
- must bind strongly to oxygen and release oxygen easily
- gives up O2 easily in capillaries, where need for it is great
- different quaternary structures in the bound and unbound forms
hemoglobin
-has 4 heme groups, so it can bind 4 oxygen molecules
hemoglobin
when one oxygen molecule is bound, it becomes easier for the next to bind
Positive cooperativity –
IS the oxygen binding ability of myoglobin affected by the presence of H+ and CO2?
No!
