This study examined differences in the structure and stability of alpha-lactalbumin (LA) proteins from cows and camels. The researchers found: 1) Camel LA was more stable than bovine LA against thermal and pH-mediated denaturation but less stable against guanidine-mediated denaturation. 2) Camel LA aggregated faster and had more intrinsic disorder than bovine LA. 3) Bovine LA underwent two structural transitions at pH 5 and 8.5, while camel LA transitioned at pH 4, indicating camel LA is more stable against changes in pH.

1. Alpha-Lactalbumin: Of Camels and Cows
Redington, Jennifer1. Breydo, Leonid1. Redwan, Elrashdy2. Almehdar, Hussein2.
Uversky, Vladimir1.
1Dept. of molecular Medicine, USF. 2Dept. of Biological Science, King Abdulaziz University
Objective
Methods
Results
Conclusion
α-Lactalbumin (LA) is a protein present in the milk of
almost all mammalian species. Since camel milk has been
attributed with various medicinal properties not found in
bovine milk, we are examining the differences between
bovine and camel LA.
We analyzed the effects of pH, calcium, temperature,
and guanidine hydrochloride (GndCl) on the secondary
and tertiary structures using Far- UV CD and
fluorescence. Aggregation studies were done with
reduced forms of bovine and wild-type camel LA using
Thioflavin T fluorescence. Quenching studies were done
using acrylamide. The amount of intrinsic disorder in
camel and bovine LA sequences was analyzed using
DisProt.
There are several structural differences between bovine
and camel alpha-lactalbumins. Camel LA is more stable
than bovine LA towards thermal and pH-mediated
denaturation but less stable towards guanidine-mediated
denaturation, aggregates faster and is more disordered
than bovine LA.
The Effect of pH on Alpha-LA
Disorder of Bovine and Camel LA
The Effect of Calcium on Alpha-LA
The Effect of GndCl on Alpha-LA
Thermal Denaturation of Alpha-LA
Protein Ksv
Bovine LA 6.1788
W Camel LA 3.8005
Quenching: Stern-Volmer Plot
Bovine LA has two transitions towards
a more disordered structure: at pH 5
and pH 8.5. Both wild-type and
recombinant camel LAs have a single
transition at pH 4.
Bovine LA denatures at 2 M GndCl. Wild-type camel LA
denatured at 1.5 M GndCl while recombinant camel
denatures at 1.6 M GndCl
Both camel LA and bovine LA showed some loss of
secondary structure in the presence of EGTA which
removes calcium.
Both bovine and camel proteins had a Tm of 53-56°C
alone or in the presence of calcium chloride. The Tm of all
proteins dropped in the presence of EGTA, bovine to 28°C,
WT camel to 34°C, and R camel to 42°C.
Aromatic residue
accessibility was
higher for bovine LA
than for camel LA.
Camel LA is more disordered than bovine LA. Wild-type
camel LA aggregated much faster than bovine LA (data
not shown).