RGI 7 Haemoproteins_I

Page 3: Oxygen Transport and Storage Proteins

• Haemoglobin:

  • Found in red blood cells; primary function is O2 transport.

  • Contains ~65% of bodily iron.

• Myoglobin:

  • Located in muscle cells; stores and transports O2.

  • Contains ~6% of bodily iron.

Page 4: Structure of Myoglobin

• Tertiary Structure:

  • Composed of a haem group (Fe(II) protoporphyrin IX) and a globin chain.

• Globin Chain Details:

  • Comprises 153 – 160 amino acid residues.

Page 5: Protein Structure

• Primary Structure:

  • Refers to the linear amino acid sequence in the polypeptide chain held by peptide covalent bonds.

• Secondary Structure:

  • Involves regular structures like alpha helices and beta sheets, stabilized by hydrogen bonds.

Page 6: Tertiary and Quaternary Structures

• Tertiary Structure:

  • The overall three-dimensional structure formed by folding of alpha helices and beta sheets, influenced by salt bridges and disulfide bonds.

• Quaternary Structure:

  • Structure of multi-subunit proteins, stabilized by non-covalent interactions and disulfide bonds.

Page 7: Iron – Protoporphyrin IX

• Features of Porphyrins:

  • Tetradentate and planar ligands with four nitrogen donor atoms.

  • Comprise four pyrrole-like rings linked by CH groups.

  • peripheral subunits

Page 8: Myoglobin Molecule

• Shape:

  • Myoglobin presents a compact shape with protein folded around the haem group.

• Linkage:

  • Globin chain linked to haem group via a histidine residue (proximal histidine).

Page 9: Structural Characteristics of Myoglobin

• Helical Regions:

  • 8 major helical regions; non-helical regions are loops.

• Interior/Exterior Characteristics:

  • Interior of myoglobin is hydrophobic while the exterior is hydrophilic, with crucial histidine residues enabling biological activity.

Page 10: 3D Structure of Myoglobin

• Observations:

  • Globular nature with planarity of haem group.

  • Examination of H bonds and absence of bonds around the haem group indicates stabilizing interactions.

Page 11: Coordination Sphere of Haem Iron

• Coordination Number:

  • In Fe(II), CN = 5 (coordinatively unsaturated) allowing for an open site for oxygen binding.

Page 12: Structure of Myoglobin

• Direct Linkage:

  • Reaffirms the proximal histidine linkage to the haem group.

Page 13: Hemoglobin Overview

• Haem Group Environment:

  • Haem located in a hydrophobic crevice to prevent oxidation when exposed to O2 and H2O.

Page 14: Preventing Oxidation

• Iron States:

  • Important to maintain iron(II) state for O2 binding, preventing oxidation to iron(III).

Page 15: Forms of Myoglobin (Mb)

• Forms of Myoglobin:

  • Myoglobin (Fe(II), His) = Purple red.

  • Oxymyoglobin (Fe(II), His & O2) = Bright red.

  • Metmyoglobin (Fe(III), His & H2O) = Brownish-red; does not bind O2.

Page 16: Color of Red Meat

• Forms of Myoglobin:

  • Color variations influenced by states of myoglobin (deoxygenated vs. oxygenated).

Page 17: Spin States of Iron(II) in Myoglobin and Oxymyoglobin

• Spin Configurations:

  • High spin (paramagnetic) myoglobin vs. low spin (diamagnetic) oxyhaemoglobin

  • configurations determined by ligand environments.

  • The octahedral complexes are dependent on the surrounding ligands

  • orbitals are split from axial to interaxial

Page 18: D6 Ion Consideration (FeII)

• Configurations:

  • Fe(II) can exhibit both high-spin (paramagnetic) and low-spin (diamagnetic) forms depending on environment.

Page 19: Metal Ion Behavior in Myoglobin

• Myoglobin & Oxymyoglobin:

  • Myoglobin features out-of-plane Fe(II), high spin, and an empty site CN=5; while oxymyoglobin features in-plane Fe(II) low spin that is saturated. ( electrons are concentrated to 3 orbitals) CN=6

Page 20: Myoglobin and Oxymyoglobin

• Structural Details:

  • MYOGLOBIN IS OUT OF PLANE RING, OXY IS IN THE PLANE RING

Page 21: Haemoglobin Structure

• X-ray Structure:

  • Haemoglobin solved by Perutz in 1959; features a near-spherical shape with positional similarity to myoglobin but different amino acid distributions.

  • THERE IS 4 MYGLOBIN SUBUINTS 2 ALPHA 2 BETA WITH SALT LINKAGES BETWEEN THEM.

Page 22: Principal Adult Human Haemoglobin (HBA)

• Tetrameric Structure:

  • Consists of 2 alpha and 2 beta chains (α2β2), with each alpha interacting between both beta chains

Page 23: Subunit Interactions

• Salt Bridge Linkages:

  • Key interactions that stabilize protein structure through opposite charges in amino acids.

Page 24: Subunit Haem Groups

• Similarities:

  • Each haem resembles that of myoglobin; characterized by a vacant coordination site for O2.

  • they are unsaturated

  • is d6 with 4 unpaired e-

  • lies out of the plane of the porphyrin ring.

Page 25: 3D Structure of Haemoglobin

• Structural Observations:

  • Highlights annealed nature of subunit interfaces, location of haem groups, and amphipathic properties.

Page 26: Iron(II) Movement

• Mechanical Depiction:

  • Explains the process of iron(II) transition and movement into the porphyrin plane upon O2 binding.

Page 27: Structural Similarity

• Comparison with Myoglobin:

  • Similar 3D structures between myoglobin and haemoglobin but with significant differences in amino acid identities.

Page 28: Myoglobin vs. Haemoglobin

• Structural Details:

  • Distinct primary structures with similarities in secondary and tertiary structures; haemoglobin possesses quaternary structure.

Page 29: Oxygenation Changes in Haemoglobin

• Transition Details:

  • Deoxyhemoglobin to oxyhemoglobin transition with notable variations in coordination numbers and magnetic properties.

  • Deocyhemaglobin is unstaturated highspin paramagnetic out of the porphyrin plane.

  • Oxyheamoglobin

  • is saturated

  • with low spin diamagnetic

  • iron is in the porphyrin plane

Page 30: Reversible Oxygenation

• Reversibility of Binding:

  • Oxygenation process of haemoglobin exhibits reversibility as encoded in chemical equations.