Hemoglobin, Oxygen Binding, and Bohr Effect

Hemoglobin and Oxygen Binding

• Hemoglobin undergoes a structural change when binding oxygen.
• Oxygen binds to the T state (low affinity), causing a conformational change to the R state (high affinity).
• Alpha-beta subunit pairs slide past each other and rotate, narrowing the packet between beta subunits.
• Low-affinity (T state) and high-affinity (R state) are key characteristics of hemoglobin's oxygen-binding behavior.
• The first oxygen molecule binds with low affinity
• The resulting conformational change in adjacent subunits leads to high-affinity oxygen binding.
• A sigmoidal binding curve facilitates high-affinity binding in the lungs and lower affinity in tissues.

Bohr Effect

• Protons and carbon dioxide promote oxygen release.
• The Bohr effect is the stimulation of oxygen release by carbon dioxide and hydrogen ions.
• Actively metabolizing tissues generate hydrogen ions and carbon dioxide.
• Carbon dioxide and water react to form hydrogen ions and bicarbonate via carbonic anhydrase.
• Increased hydrogen ion concentration (decreased pH) occurs in the blood near the tissues relative to the lungs.

pH Influence

• Oxygen binding is influenced by pH levels.
• Hydrogen ions bind to hemoglobin and stabilize the T state.
• The T state exhibits low oxygen affinity binding.

Hemoglobin and Carbon Dioxide

• Carbon dioxide is produced by metabolism in tissues and must be exported the form of a carbamate on the amino terminal residues of each of the polypeptide subunits.
• High carbon dioxide levels in tissues cause some carbon dioxide to bind to hemoglobin.
• This binding decreases hemoglobin's affinity for oxygen, resulting in its release.
• High oxygen in lungs causes oxygen to bind to hemoglobin, also releasing carbon dioxide.
• Carbamate formation yields a proton, contributing to the Bohr effect
• Carbamate forms additional salt bridges, stabilizing the T state.

Hemoglobin Oxygen Affinity Change

• Increased hydrogen ion and carbon dioxide levels in the blood near tissues relative to the lungs favor the T state, resulting in oxygen release.
• H+ protonates His146, forming a salt bridge with Asp94, which favors the T state transition.
• Lower affinity for oxygen releases oxygen in the tissues.
• Carbon dioxide covalently attaches to the N-terminal residue of hemoglobin and releases H+.
• Additional salt bridge forms, which stabilizes the T state.
• Very high oxygen partial pressure triggers hemoglobin's T to R transition in the lungs.
• Fe in heme moves, conformational changes break Asp94 and His146 salt bridges.
• His146 is deprotonated, hydrogen ions are released, and carbon dioxide is released.

2,3-BPG Regulation

• 2,3-BPG regulates oxygen binding.
• A small, negatively charged molecule binds to hemoglobin's positively charged central cavity to stabilize the T state.
• 2,3-BPG is present in mM concentrations in erythrocytes.
• It is a negative heterotropic regulator of hemoglobin

2,3-BPG Binding

• 2,3-BPG binds to the central cavity of hemoglobin.
• BPG binds between beta subunits in the T state.
• Positively charged cavity interacts with negatively charged BPG.
• Only one 2,3-BPG binds per hemoglobin molecule.
• It stabilizes the T state and promotes oxygen release.

2,3-BPG and Adaptation

• 2,3-BPG allows oxygen release in tissues and adaptation to altitude changes.
• Sea level means around 40% of oxygen is delivered to tissues.
• High altitudes have lower partial pressure of oxygen and deliver 30% reduced levels of oxygen.
• The body increases BPG, reducing hemoglobin affinity for oxygen.
• The release of oxygen in tissues is at 40% when delivery is restored.

Immune System

• Immune response involves intricate and coordinated interactions between proteins,molecules, and cell types
• Humoral response: responds to foreign cells and proteins by using B cells, immunoglobulins
• Cellular response destroys host cells infected by foreign agent such as viruses by using T cells

Antigens and Epitopes

• Antigen: any molecule/pathogen that triggers an immune response, e.g., viruses.
• Epitope (antigenic determinant): specific molecular structure on an antigen recognized by antibodies/T-cell receptors

Immunoglobulins

• Immunoglobulins (IgGs) form a major class of antibody molecules and are among the most abundant serum proteins.
• Made of four polypeptide chains noncovalently linked by S-S bonds.
• Has two heavy and two light chains.
• Cleavage with papain (protease) yields basal fragment = Fc and antigen-binding fragment = Fab.
• Each chain has identifiable constant and variable domains.
• Constant domains have the immunoglobulin fold, a well conserved structural motif
• Variable domains make up the antigen-binding domain.

Immunoglobulin Structure

• IgG has an all-beta class of proteins.
• Conformational flexibility is important for function.

Immunoglobulin Classes

• Each class has a characteristic heavy chain.
• There are two types of light chains.
• IgD, IgE, and IgG have similar overall structures.
• IgM occurs as a monomer or pentamer.

IgG Binding

• Binding specificity is determined by variable domains of heavy and light chains
• Binding is conferred by chemical complementarity between antigen and binding site
• Conformational changes via induced fit to facilitate complementation groups.
• Kd values as low as 10^-10 M means a strong anitbody-antigen interaction
• Lower Kd = stronger binding-affinity

Antibodies for Detection

• Antibodies are used as detection agents for ELISA, Western Blot, and Microscopy.

Molecular Motors

• Organisms, Cells, Organelles, Macromolecules all move to perform function
• Migration of organelles along Micrtubules
• Motion of Flagella,
• Movements of proteins along DNA
• Contractile proteins of skeletal muscle
• Fueled by Chemical Eenergy like ATP
• Large Aggregates and proteins under go Cyclic Conformation Changes

Muscle Proteins Myosin/Actin

• Important muscle proteins include myosin and actin
• Myosin: comprised of 6 subunits, including 2 heavy and 4 light chains.
• Heavy Chains: Are the overall structure with C terminus being extended alpha helices.
• N term globular domain for atp hydrolysis.
• Light Chains: Globular domain and heavy chains
• Thick Filaments: fibrous tails associate to form bipolar structure.
• Globular project from either end

Actin Characteristics

• Actin: In muscles, monomeric actin = G-actin
• Forms long polymer=F Actin.
• Two fillaments around right handed fashion
• Creates thin fillament with proteins troponin
• Troponin allows actinin monmer thin fillament

Muscular Structure

• Thick filaments that combine = muscular structure, with skeletal muscles.
• Muscular structure consist of bundle of muscle fibers.
• With 1k myofribrils to make complex proteins to thin and thick fillaments.
• Fillaments and fibers alternate sections of A/I bands
• A bands high electron density of overlapping thin/thick fillaments.
• Bisected Y M line of tick fillament
• I bands have low electron density. thin fillament, bisected anchors fillament

Muscle Contractions

• The slide past each other to perform muscular contractions
• Contractions narrows disks and bands perform contracts

Muscle Contraction Mechanism

• Four main steps: ATP binds to myosin, clefot opens.
• The actin released after the interaction.
• ATP Hydrolysis: Conformational changes to make high energy where myosin weakly bonds to F actinn
• Closer closer to Z disk.
• Myosin cleft Strenghthens where the PI is relaased
• Power Stoke: Conformational change to resting to pull tail toward z disk

Muscle System Regulation

• Thin fillaments contain troponin, tropomyosin complex
• Muscle contractions
• Bonds attach sites blocks the attachment. Repressors thin filelents
• Calucim: Binds to thin fillament, blocks bindind the actin-myosin

Sickle Cell Anemia Genetic

• Hereditary Disease with Autosomal Recessive that causes single amino acid variant with quaternary tertiary structure in cells
• Occurs the glutamic sequence with determining the protein

Sickle Cell Genetic

• Amino acid in Beta Subunit that causes strands from molecule
• Deformed Sickle Shape Erythrocytes
• Hemoglobin conent about half and is very fragile due to lock of blood from Anemia.

Sickle Cell Genetic Hypothesis

• High In Africa unusually in cell to confer evolutionary advantage compensate with early death
• Carriers confer high resistance to lethal malria(>90)

Antibody Treatment Properties

• Has greater 100 therapeutics in many diseases that keep getting approved with treatment of various human disesaes
• Engineered Antibody
• Treat infectious Inflammations
• Select tumor for uptake
• Reduce resistance
• Target cancer

Antibody Treatments Monoclonal

• Antiboidies coming from B to recognize epitope. Block cell recepttors and inhibity viral enrty.
• Nuetralze it and viris
• Spile proteins to the epitope so the virus can enter.

Anticancer

50 percent approvals for antibody therapies, modify enhance fx and for growth in hibiters, increases safely and efforet

Explore hemoglobin's structural change upon oxygen binding and the transition from T state (low affinity) to R state (high affinity). Understand how this conformational shift enhances oxygen binding. Learn about the Bohr effect, where protons and carbon dioxide facilitate oxygen release, crucial for metabolizing tissues.