1. PROTEINS i. FIBROUS PROTEINS Collagen Elastin Keratin
ii. GLOBULAR PROTEINS
Myoglobin
Hemoglobin

2. COLLAGEN STRUCTURE Triple helix
Has 3.3 residues per turn and a rise per residue nearly twice that of an -helix
Every 3rd amino acid residue is a glycine residue
Gly-Pro-X or Gly-Hyp-X

4. Hydroxyproline (Hyp) Result from hydroxylation of proline residue
Stabilizes the triple helical structure of collagen
Ascorbate

5. Biosynthesis of Collagen

6. Biosynthesis of Collagen
Biosynthesis of Collagen
1. Synthesis of a chains of pre-procollagen on ribosomes. A signal protein directs them to the RER .
m-RNA
Signal protein

7. Peptidyl lysine hydroxylase Proline Hydroxyproline
2.     Cleavage of signal protein forms procollagen
3.     Hydroxylation of lysine and proline
Lysine Hydroxylysine
Peptidyl lysine hydroxylase
Proline Hydroxyproline
Peptidyl proline hydroxylase
Ascorbic acid is necessary to activate the hydroxylases OH

8. 4. Glycosylation
Addition of galactose and glucose to some hydroxylysine residues.
The enzymes galactosyl transferase and glycosyl transferase are required for this process. OH

9. 5. Assembly of three  - chains to form procollagen
This involves the formation of disulfide bonds between parts of the polypeptide chains known as registration peptides, which occur at both ends of the pre-procollagen.
The assembly process aligns the three a - chains relative to one another.
The three alpha chains are wound around one another in the form of a triple helix.
The assembly process occurs in the Golgi apparatus. S
Registration peptides

10. 6. Secretion of procollagen molecules by exocytosis into the extra cellular space

11. 7. Cleavage of registration peptides
Occurs in the extra cellular space, and is catalysed by procollagen peptidases.
The resulting molecule is called tropocollagen.
Procollagen peptidase

12. 8. Self-assembly or polymerization of
tropocollagen molecules form collagen fibrils
Cross-linkage between adjacent tropocollagen molecules stabilizes the fibrils.
It involves the removal of an amino group (NH2), which has a net oxidative effect and the formation of covalent cross-links.
It is catalyzed by lysine oxidase (or catalase).

13. Ehlers-Danlos Syndrome
Inheritable defects in collagen molecule
Characterized by stretchy skin and loose joints
Due to defect in genes that encode -collagen-1, procollagen N-peptidase, or lysyl hydroxylase

14. COLLAGEN DISEASES Osteogenesis imperfecta Brittle bone syndrome
Bones easily bend and fracture

15. COLLAGEN DISEASES Menke’s syndrome
Characterized by kinky hair and growth retardation
Due to dietary deficiency of copper required by lysyl oxidase, which catalyzes a key step in the formation of the covalent cross-links that strengthen collagen fibers.
Less than 1 in 1,250,000 children will be born with Menkes Disease, otherwise known as Kinky Hair Syndrome.
Menkes is a genetic disorder caused by a mutation usually primarily in the Y Chromosome (boys) it affects the copper levels and metabolism in the body causing seizures, brain damage, weakened bones and muscles, organ shutdown and failure to thrive.
There is no cure and unless caught within days of birth medication and treatment is only symptomatic.
Children with the disease will die before their first decade of life, most dying within infancy or toddlerhood.

16. Scurvy Best known defect in collagen biosynthesis
Deficiency of Vit.C (required by prolyl and lysyl hydroxylases)
Bleeding gums, swelling joints, poor wound healing, and ultimately death.

17. Elastin Connective tissue protein with rubber-like properties
Found in lungs, walls of large blood vessels, and elastic ligaments
Can be stretched to several time their normal length, but recoil to their original shape when relaxed

18. STRUCTURE OF ELASTIN
Composed primarily of small non polar amino acid residues (e.g. G, A, V)
Also rich in proline and lysine, but contains little hydroxyproline and hydroxylysine
Interchain cross-links form desmosine residues

19. DESMOSINE CROSS-LINK
An extensively interconnected, rubbery network that can stretch and bend in any direction when stressed, giving connective tissue elasticity

20. Role of -1 antitrypsin in elastin degradation
Inhibit neutrophil elastase (protease that degrades elastin of alveolar walls)
Deficiency of -1 antitrypsin leads to destruction of the alveolar walls of the lungs resulting to EMPHYSEMA
Treatment :
Administration of -1 AT

21. Role of -1 antitrypsin in elastin degradation
As we breath, we not only take in oxygen, but we also take in our environment.
Pollen, sawdust, car exhaust, dander, paint fumes and over-spray, radon gases, hair sprays, perfumes, household cleansing fumes, tobacco smoke and many other pollutants

22. Role of -1 antitrypsin in elastin degradation
Elastase - the lungs natural defense against the irritants
Elastase (shown as white dots) attach themselves to the foreign material in the sac and consumes it as well as bacteria in the lungs

23. Role of -1 antitrypsin in elastin degradation
Once the lungs has been cleaned, antitrypsin deactivates elastase

24. Role of -1 antitrypsin in elastin degradation
Without the antitrypsin enzyme, the elastase continues to consume anything in its path, including healthy lung tissue

25. Role of -1 antitrypsin in elastin degradation
As the healthy lung (sac) tissue is destroyed, the once stretchy walls of the sac become stiff and enlarged with air.
The enlarged sacs no longer have the ability to exchange oxygen and carbon dioxide with the bloodstream.
The lungs poor elasticity causes the lungs not to deflate properly trapping air leading to over-inflation of the lungs.
This is known as emphysema.

26. Pathogenesis of Empysema

27. - KERATIN Proteins that forms tough fibers
Found in the hair, nails, and outer epidermal layers of mammals
Constituents of intermediate filaments of cytoskeleton in certain cells
Rich in Cys, -S-S- cross-links between adjacent polypeptide chains resulting to fibers that are insoluble and resistant to stretching

28. GLOBULAR HEMEPROTEINS
Group of specialized protein that contains heme
Maintain a supply of oxygen essential for oxidative metabolism
MYOGLOBIN
HEMOGLOBIN

29. HEME Fe+2- protoporphyrin IX A cyclic tetrapyrrole
A planar network of conjugate double bonds absorbs visible light and colors heme deep RED.

30. MYOGLOBIN (Mb)
A monomeric protein (153 amino acid residues) of the red muscles
Used in some tissues, notably muscle,
as a storage reserve of O2 and
for intracellular transport of O2

31. Myoglobin Structure
78%  helical (the other 22% in  turns and short loops, no  sheet at all)
8  - helices designated by letters A-H, in an N to C terminal direction, and connections between helices are referred to as "AB", "CD", etc.
Polar amino acid residues are found at the surface
Non polar amino acid residues (L, V, F, & M) are found at the interior except His E7 and HisF8

32. Myoglobin structure
The heme of myoglobin lies in crevices of helices E and F
Distal histidine
Proximal histidine

33. HEMOGLOBIN Found exclusively in red blood cells
Its main function is to transport oxygen from the lungs to the capillaries of the tissues
The oxygen-binding properties of hemoglobin are regulated by allosteric effectors

34. Hemoglobin
Heterotetramer: 2 -subunits (gray and light blue) + 2 - subunits (pink and dark blue)
(NOTE: designation of individual polypeptide chains with greek letters has nothing whatever to do with their secondary structural elements!)

35. Subunit composition of principal hemoglobin
22 - Hemoglobin A (HgA) is the major hemoglobin in adults
22 - Fetal hemoglobin (HbF)
2S2 - Sickle cell hemoglobin (HbS)
22 - Minor adult hemoglobin (HbA2)
Myoglobin and the  polypeptide of hemoglobin A have almost identical secondary and tertiary structures

36. Quaternary structure of hemoglobin
Hgb tetramer is composed of two identical dimers, ( )1 and ()2, dimers 1 and 2 respectively
Dimers are held together by hydrophobic interactions
Ionic and H-bonding also occur between the members of the dimer

37. Conformational Changes resulting from oxygenation and deoxygenation of hemoglobin
T form or “Taut” (tense) form
Deoxy form of Hgb
Two  dimers interact through a network of ionic bonds and hydrogen bonds
Low oxygen-affinity form of hemoglobin

38. Conformational Changes resulting from oxygenation and deoxygenation of hemoglobin
R form or Relaxed form
Binding of oxygen to Hgb (oxyhemoglobin)
Some ionic bonds and H-bonds between the  dimers are ruptured thus, the polypeptide chains have more freedom of movement
High oxygen-affinity form of hemoglobin

40. Shift from deoxy to oxy conformation
Fe lies out of plane of heme ring
Fe moves into plane of heme ring
Shift from deoxy to oxy conformation

41. OXYGEN BINDING TO MYOGLOBIN
Can bind only one molecule of oxygen (one heme group only)
The oxygen dissociation curve for Mb is a hyperbolic shape
Mb reversibly binds a single molecule of oxygen
Mb + O2  MbO2

42. OXYGEN BINDING TO MYOGLOBIN
HEMOGLOBIN
4 O2 binding sites per molecule
The oxygen dissociation curve for Hgb is sigmoidal in shape
Subunits cooperate in binding oxygen

43. Cooperative binding of Oxygen
It means that the binding of an oxygen molecule at one heme group increases the oxygen affinity of the remaining heme group in the same Hgb molecule
This is referred to as heme-heme interaction

44. Cooperative Interactions (allosteric interactions)
[Greek: "allos"="other", "stereos" = space] occur when binding of one ligand at a specific site is influenced by binding of another ligand, which is called an "allosteric effector" or "modulator" 
The second site is also called an allosteric site

45. Cooperative Interactions (allosteric interactions)
Homotropic interaction/effect
the interacting sites all bind the same ligand (e.g., binding of O2 at one site on Hb influences the binding affinity for O2 of another site)
Heterotropic interaction/effect
the interacting sites bind different ligands

46. Homotropic Interaction/Effect
Positive homotropic effect
the homotropic effector increases the binding affinity for the same kind of ligand at other sites
O2 in the hemoglobin system increases the O2 binding affinity of other sites

47. Heterotropic Interaction/Effect
Negative heterotropic effector or allosteric inhibitor
the effector decreases the binding affinity for the primary ligand
protons, or CO2, or 2,3-BPG; all are negative heterotropic effectors of O2 binding to hemoglobin
Positive heterotropic effector, or allosteric activator
effector increases the binding affinity for the primary ligand

48. The Bohr Effect - effect of binding of protons (H+) and CO2 on O2 binding affinity of Hb
HbO2 + H+  HbH+ + O2
Deoxyhemoglobin
Increase protons or a lower pO2
Oxyhemoglobin
Decrease protons or an increase pO2

49. Binding of Carbon dioxide
CO2 is a negative heterotropic effector (allosteric inhibitor) of O2 binding to Hb
Presence of CO2 in the tissues reduces affinity of Hb for O2 (favors deoxy, T state) in two ways:
1. CO2 lowers the pH (Bohr effect)
2. CO2 participates in formation of carbamates by the N-terminal a-amino groups of Hb:
Formation of carbamate releases H+, which contributes to the Bohr effect
Carbamate formation (CO2 binding) favors the deoxy state.

50. Binding of CO
CO binds tightly (but reversibly) to the Hb iron, forming carbon monoxyhemoglobin, HbCO
CO binding to one or more of the 4 heme sites of Hb shifts to relaxed conformation
The affinity of Hb for CO is 220X greater than for oxygen

51. Binding of CO 60% of HbCO are fatal
CO poisoning is treated with Oxygen therapy, which facilitates the dissociation of CO.

53. 2,3-bisphosphoglycerate (2,3-BPG) or "2,3-diphosphoglycerate" (DPG)
Most abundant organic phosphate in the red blood cells
Binds strongly to the deoxy form of Hb (T state), but only very weakly to oxy form (R state)

54. 2,3-bisphosphoglycerate (2,3-BPG) or "2,3-diphosphoglycerate" (DPG)
Favors/stabilizes the T form, reducing the O2 binding affinity of Hb (shifts binding curve to the right)
Increased concentration of 2,3-BPG, reduce affinity of hemoglobin for O2which increases the efficiency of O2 delivery (enhances RELEASE) to tissues

55. 2,3-bisphosphoglycerate (2,3-BPG) or "2,3-diphosphoglycerate" (DPG)
Increase concentration of 2,3-BPG is observed in:
Chronic hypoxia (observed in Obstructive Pulmonary Emphysema)
High altitudes
Chronic anemia

56. MUTANT HUMAN HEMOGLOBINS
METHEMOGLOBIN
The heme iron is ferric than ferrous
Oxidation of ferrous to ferric is caused by the side effects of drugs such as sulfonamides, or endogenous substance like hydrogen peroxide
Can neither bind nor transport oxygen
HEMOGLOBIN M
– HisF8 has been replaced by tyrosine
HEMOGLOBIN S
V has replaced Glu6 of the -subunit

57. BIOMEDICAL IMPLICATIONS
MYOGLOBINURIA
Dark red coloration of urine following massive crush injury because myoglobin is released from damaged muscle fibers
A N E M I A S
Reduction in the number of RBC or of Hb in the blood, or impaired production of erythrocytes (Vit.B12 deficiency)

58. BIOMEDICAL IMPLICATIONS
THALASSEMIA
Partial or total absence of one or more  (-thalassemia) or  (-thalassemia) chains of hemoglobin
GLYCOSYLATED HEMOGLOBIN (HbA1c)
Glucose enters the erythrocytes and glycosylates the -group of lysine residues and the amino terminal of Hb
Reflects the mean blood glucose concentration thus provides valuable information for management of Diabetes Mellitus