Biochem Lecture 10

Sickle cell anemia

is a molecular disease of hemoglobin

• homozygous condition

• single amino acid substitution (Glu6 to Val6) in β chains produces a hydrophobic patch

Single mutation

Glu6 → Val in the Beta chain of Hemoglobin

the new valine side chain can bind to a different Hb molecule to form a strand similar to the amyloidgenic proteins

What occurs

This sickles the red blood cells.

• Untreated homozygous individuals generally die in childhood.

• Heterozygous individuals exhibit a resistance to malaria.

Normal and sickle cell hemoglobin

In people with sickle cell anemia, both alleles of Hb β-chain gene are mutated.

• deoxygenated hemoglobin, but not oxy-Hb, becomes insoluble and forms polymers that aggregate

• normal hemoglobin remains soluble upon deoxygenation

Mehtemoglobinemia

• Occurs when red blood cells (RBCs) contain methemoglobin (MetHb) at levels higher than 1%.

• Methemoglobin results from the presence of iron in the oxidized ferric form (Fe3+) instead of the usual reduced ferrous form (Fe2+).

Thalassemias

• Genetic mutations in the alpha (α) or beta (β) globin genes (alpha or beta-thalassemias)

• These mutations reduce or stop the production of globin chains, leading to imbalanced hemoglobin and destruction of red blood cells.

Sickle Cell anemia treatment

• medications to reduce pain and prevent complications, and blood transfusions, as well as a bone marrow transplant

• Supplemental Vit B9 (folic acid): enhance red blood cell production (erythropoiesis) in the bone marrow

• Hydroxyurea to induce HbF

Casgevy

• Disables the BCL11A gene enhancer in hematopoietic stem cells.

• BCL11A normally suppresses fetal hemoglobin (HbF).

• By silencing BCL11A, HbF is reactivated, which replaces the faulty adult hemoglobin (HbS).

• HbF doesn’t sickle — alleviating symptoms.

Interactions between proteins and ligands

occurs in immunoglobins (antibodies)

Examples: Diagnostics and lab testing and biologic drugs and monoclonal antibodies

Antibodies

have two identical antigen-binding sites

Immunoglobulin (IgG)

major class of antibodies

• one of the most abundant blood serumproteins

• 4 polypeptide chains: 2 heavy chains and 2 light chains

• cleavage with protease papain releases the basal fragment Fc and two Fab branches (each with a single antigen-binding site)

• constant domains contain the immunoglobulin fold structural motif

Antibodies bind

tightly and specifically to antigen

Induced fit

conformational changes in the antibody and/or antigen allow the complementary groups to interact fully

Polyclonal antibodies

produced by injecting a protein into an animal

• contain a mixture of antibodies that recognize different parts of the protein

• multiple epitopes

Monoclonal antibodies

• Synthesized by a population of identical B cells (a clone)

• homogeneous, all recognizing the same epitope.

ELISA

Antibody–Antigen interaction can be used for the quantitative assessment of an antigen in a sample (e.g., HIV, malaria, Hep B, etc)

Western blots

immunoblot = western blot assay and uses antibodies to detect a protein