Hemoglobin Presented to Bioinformatic MN1 10 p course, Spring term 2006 by Amirah Khan With acknowlegment to Miriam Geörg & Björn Garpefjord

Hemoglobin – 3D Structure Tetrameric complex  2  2 Chain A = Chain C Chain B = Chain D 1 heme group per subunit/chain CATH Classification CMainly Alpha (1) AOrthogonal Bundle TGlobin-like HGlobin

How may the structure of hemoglobin be stabilised?

N-capping of helices Helix: Ala53 – Ala71 Removal of Ala53 Replaced by Asp, negatively charged  Reduced dipole moment

Reduced dipole moment in helix Indication of H-bond to Gly57 More stable? N-capping of helices

Reducing the Flexibility of the Main Chain  Stabilization of exposed loop by mutating Gly to Pro Mutation: G51 P

Stabilizing the Quartenary Structure The hemoglobin tetramer consists of 2  dimers. The interface between those 2 dimers is important for flexibility and funcionality.  Stabilization of the  dimers by creation of disulfide-bonds between the subunits Mutations:  chain: Ala 123 Cys  chain: Val 33 Cys

Stabilizing the Quartenary Structure

Stabilizing the Hydrophobic Core The main pocket of each chain is occupied by the heme group which is essential for function.  Mutations in these pockets might interfer with heme binding and thus oxygen transport.

Increasing the Oxygen - Affinity In nature there exist different forms of hemoglobin: Adult hemoglobin (  2  2 ) Fetal hemoglobin (  2  2 ) with higher oxygen affinity  Increase of Oxygen Affinity by mutating the aa’s close to the coordinative His 92 to the corresponding aa’s in fHb Coordinative Histidine

Increasing the Oxygen - Affinity

Stabilization vs Flexibility Stabilized Structure Industrial Applications? Conserved Structure Optimized by evolution!!! Flexibility of subunits needed for protein function –Induced fit: conformational change after binding of first O 2 leads to increased affinity for following O 2 molecules –Large pockets occupied by essential heme group Single aa exchange in Sickle Cell Anemia causes aggregation of hemoglobin