CLINICAL ASPECTS OF BIOCHEMISTRY
PROTEINS AND DISEASE
HAEMOGLOBIN AND HAPTOGLOBIN
Haemoglobin - revision
Haemoglobin variants - haemoglobinopathies
Haemoglobin S
Thalassaemia
Haptoglobins
HAEMOGLOBIN - REVISION
Myoglobin (Mb) Oxygen binding/storage protein in muscle;
may also play a part in local oxygen transport. O2 binds to haem.
Maintenance of haem in Fe2+ form is necessary for O2 binding.
Mb is a monomeric protein of about 150 aa.
Haemoglobin A (HbA) O2 carrier in blood (red cells).
Tetramer: 22. Quaternary structure allows allostery - cooperative binding of O2 modulated by pH (Bohr effect), CO2
binding, bisphosphoglycerate (BPG) binding. 3D structure of
each chain is similar to that of Mb.
HAEMOGLOBIN
TERTIARY STRUCTURE OF MYOGLOBIN AND
HAEMOGLOBIN  SUBUNIT
Different types of Hb in man:
HbA 22
HbA2 22 ~2% of adult Hb;  chain differs from  at ~ 10% of residues;
function (if any) unclear
HbF 22 late foetus and neonate; replaced by HbA 3-6 months after birth; 
chain differs from at ~of residues. In presence of BPG HbF has higher
affinity for O2 than HbA, allowing transfer of O2 to foetus (2 HbFs in man,  chains
differing at 1 aa)
HbGower Gower I 22 Embryonic.  similar to  (~20% differences)
Gower II 22 Embryonic.  similar to  (~40% differences)
So, at least 5 different Hbs (6 chains) in normal human. , , d,  chains can all
form tetramers,  can't.
DEVELOPMENTAL PATTERN OF HAEMOGLOBIN IN MAN
Based on Voet & Voet (1995)
EVOLUTIONARY TREE RELATING
HUMAN GLOBIN CHAINS
Mb






Hbs in lower organisms:
Mammals. Adult Hbs all similar to human HbA, but may be
variants unlike those seen in human. Developmental patterns
of Hbs differ considerably
Other vertebrates Most vertebrates have 22 type structure.
Variant types differ considerably. Lamprey (most primitive
fish) has only a single chain - more similar to Mb than
mammalian Hbs (no allostery)
Invertebrates, plants, bacteria. Hb-like proteins frequently
found, but not 22
HAEMOGLOBIN VARIANTS - HAEMOGLOBINOPATHIES
1.
Exterior of molecule
e.g. Glu6Val [haemoglobin S (HbS)]
Glu
2.
B8Lys
(harmless?)
Altered tertiary structure
Phe CD1Ser [Hb Hammersmith]
Gly
3.
B6Arg
[Hb Riverdale-Bronx]
Altered 'active site’
His
F8Tyr
[Hb Iwate] (proximal His) )
His E7Tyr [Hb Boston] (distal His)
4.
)(cyanosis; methaemoglobinaemia)
Alterations at subunit interfaces
Asp G1His [Hb Yakima] )
Asn G4Thr [Hb Kansas] )
(polycythaemia or cyanosis)
SICKLE CELL ANAEMIA - HbS - FIBRES
Based on Voet & Voet (1995)
HbS - AGGREGATION
Based on Voet & Voet (1995)
HAEMOGLOBIN S (HbS)
Possible therapies:
1. Disruption of intramolecular interactions (peptides?)
2. Use of agents to increase O2 binding affinity
3. Lower HbS concentration (increase erythrocyte
permeability)
4. Keep HbF switched on (hydroxyurea)
5. Vasodilators
6. Gene therapy
 and  THALASSAEMIAS
0 and 0 thalassaemias- corresponding globin chain missing completely
 and + thalassaemias - corresponding globin chain produced in reduced amount
 thalassaemia
1.
.
3.
4.
Silent carrier state:
thalassaemia trait:
Hb H disease:
Hydrops fetalis:
[ Hb Barts: excess 4;
1 (of 4)  genes missing
2  genes missing
3  genes missing
4  genes missing [lethal]
HbH: excess 4 ]
Also  thalassaemia due to other causes. E.g. Hb Constant Spring:
Mutant stop codon and read-through of 31 aas, but mRNA degraded, so little
protein
HAEMOGLOBIN GENE CLUSTERS
Chromosome 16

y

Chromosome 11


y1 1 2
G
20
A
40
y


60
kbp
DELETIONS IN THE HAEMOGLOBIN  GENE CLUSTER

kbp
G
20
A
40
y


60
0 thalassaemia
Hb Lepore
GA 
thalassaemia
GA HPFH
G HPFH
Hb Kenya
HPFH = hereditary persistent fetal haemoglobin
 thalassaemia
Point mutations that can cause  thalassaemia:
1. Nonsense mutations
2. Frameshift
3. Point mutation in promoter
4. Point mutations that inactivate or generate splice sites
5. Point mutations of the AATAAA sequence
HAPTOGLOBINS
 &  chains; S-S linked; tend to form oligomers ()2 etc.
In human  chain is polymorphic:
I (83 residues): IF (Lys54) and IS (Glu54)
II (143 residues):
54
Lys
Partial gene duplication
71
113
143
Glu
Gene frequencies: IF 0.16
IS
II
0.24
0.60
PROPOSED MECHANISM FOR PARTIAL GENE
DUPLICATION OF HAPTOGLOBIN

Hp1F
Hp1S
Hp2
