DENT Fun. I - Collagen & Hemoglobin

____ is the most abundant protein in animals.

Collagen

Collagen

Fibrous protein that gives the skin form and strength

Collagen is formed by ____.

fibroblasts; deposited in the ECM

Over 90% of collagen in the body is ____.

Type I Collagen; skin, bones, tendons

Collagen Primary Structure

Repeating amino sequence: Gly-X-Y where "X" and "Y" can be Proline or Hydroxyproline

Hydroxylation of Proline

Proline + O2 + Ascorbic Acid (Vit. C) + a-Ketoglutarate

Hydroxylation of Lysine

Lysine + O2 + Ascorbic Acid (Vit. C) + a-Ketoglutarate

via the enzyme, Lysyl Hydroxylase

Scurvy

Vitamin C deficiency that causes collagen malformation

Collagen Secondary Structure

Left-Handed Helix

3.3 amino acids/turn

In collagen, every third amino acid is Glycine. Because of this there is a ____ on the Left-Handed Helix.

strip of Glycine

Collagen Tertiary Structure

- Triple Helix of Left-Handed Helices intertwined to form a Right-Handed Triple Helix called Tropocollagen

- Glycine is in the middle of the triple helix

What is the basic structural component of Collagen?

Tropocollagen

Tropocollagen

RH Helix of intertwined LH Polypeptide Chains

Collagen Quaternary Structure

Alpha Triple Helix: 3 bands of Tropocollagen "super-coiled" together

5-Hydroxylysine is an attachment site for ____.

sugars

Galactose and Glucose are frequently covalently bonded to 5-Hydroxylsine via ____ and ____.

galactosyltransferase/glucosyltransferase

What do sugars attached to Hydroxylysine do?

- Organize collagen fibrils

- Act as sites of nucleation for bone mineralization

What happens in the gaps of Collagen's Quaternary Structure?

Mineralization of bone

Collagen Fibers are ____.

cross-linked

What is the major class of Collagen?

Fiber-Forming (Types I, II, and III)

Work to convert Procollagen to Collagen in the ECM

What are the 6 other classes of Collagen?

- Fiber-Associated

- Network

- Filament

- Anchoring Fibril

- Transmembrane

- Multiplexins

Fiber-Forming Collagens are ____, while other classes of Collagen are associated ____.

parallel/anti-parallel

The other Collagen classes seldom convert Procollagen to Collagen (T/F)

True

Collagen Synthesis

(1) Synthesis in the Rough ER

(2) Peptide chains form into trimers (Procollagen)

(3) Procollagen further folds and is secreted into the ECM

(4) Proteases in the ECM cleave the carboxy and amino ends, creating Tropocollagen

(5) Tropocollagens cross-link to form Collagen

____% of total body heme is located in RBCs

85

Hemoglobin (Hb)

Tetramer composed of 2 Alpha Chains & 2 Beta Chains

Myoglobin

Monomeric O2 storing protein in Muscle

Myoglobin has a Quaternary Structure (T/F)

False; it is Monomeric, so it does not associate with other protiens

Allosteric Regulation

The binding of a regulatory molecule to a protein at one site affects the function of the protein at a different site

Fe2+ is coordinated by ____.

His F8

Iron interacts with ____ ligands in Hb and Mb.

6

What are the 6 ligands Iron binds with in Heme?

- 4 Nitrogens from Porphyrin

- The Imidazole Ring of His F8

- O2

O2 binding to the Heme group causes ____.

conformational change, pulling His F8 and Fe2+ into the plane of Heme

Fe2+ moves less than ____ nm when conformational change occurs.

0.04

O2-Binding Curve

Hb has a higher affinity for O2 than Mb (T/F)

False; Mb stores O2 more readily at all O2 pressures

Cooperative Binding

The tendency of the protein subunits of Hb to affect each other's O2 binding such that each bound O2 increases the likelihood of further O2 binding

Hb binds O2 in the lungs, where the pO2 is about ____.

100 torr

Hb releases O2 in the capillaries, where the pO2 is about ____.

40 torr

O2 Binding by Hb induces a ____ structure change.

quaternary

When O2 binds, an Alpha-Beta Hb subunit moves ____ in relation to the other.

15*

R Conformational State of Hb

"Relaxed" Oxyhemoglobin

T Conformational State of Hb

"Tense" Deoxyhemoglobin

p50

The pO2 when hemoglobin is 50% saturated

P50 of Hb = ____

26 torr/mmHg

The p50 is inversely proportional to ____.

O2 affinity

ie. High p50 = Low O2 Affinity

What agents can affect Hb-O2 Binding?

- H+

- CO2

- Cl-

- 2,3-BPG

Bohr Effect

Decrease in the amount of O2 associated with Hb in response to lowered blood pH resulting from an increased [CO2] in the blood

Dissociation of O2 from Hb increases as pH decreases

Lower pH will ____ the p50 of Hb.

increase

H+ Effect on Hb

Bind directly to Hb, decreasing O2 affinity

CO2 Effect on Hb

CO2 + H2O <-> H+ + HCO3-

Increase in [CO2] = Increase in [H+]

2,3-BPG Effect on Hb

Allosteric Effector of Hb that binds a site distanced from the Heme Iron, decreasing O2 affinity

Where does 2,3-BPG bind Hb?

In a pocket formed by the 2 β chains in the center of Hb; 2,3-BPG is very electronegative so it binds the positive charges of Deoxyhemoglobin, stabilizing it

Fetal Hb has a ____ O2 affinity.

higher

Why does Fetal Hb have a higher affinity for O2?

It has a lower affinity for 2,3 BPG

Why does Fetal Hb have a lower affinity for 2,3-BPG?

Instead of 2 Beta-Chains it has 2 Gamma-Chains, which has Ser instead of His at position 143. This creates less positive charge in the pocket for 2,3-BPG to bind.

Fetal Hb

2 Alpha and 2 Gamma chains

Sickle Cell Anemia is caused by ____.

a single mutation in Beta-Globin

Creates misfolding of Hb and formation of a hydrophobic pocket in DeoxyHb. The malformed DeoxyHb will aggregate and form fibers that shape the RBCs into a sickle-shape.

Cooley's Anemia is caused by ____.

the absence of Beta-Globin chains