HemoglobinPresented to Bioinformatic MN1 10 p course, Spring term 2006 by Amirah Khan

With acknowlegment to Miriam Geörg & Björn Garpefjord

Hemoglobin – 3D Structure

Tetrameric complex 22

Chain A = Chain C

Chain B = Chain D

1 heme group per subunit/chain

CATH Classification

C Mainly Alpha (1)

A Orthogonal Bundle

T Globin-like

H Globin

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 (22)

• Fetal hemoglobin (22) 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 O2 leads to increased affinity for following O2 molecules

– Large pockets occupied by essential heme group

• Single aa exchange in Sickle Cell Anemia causes aggregation of hemoglobin