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2002
LSU-HHMI Summer Undergraduate Research Program |
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 Lauren
J. Solhjoo (Vince J. LiCata, LSU Dept. of Biological Sciences)
Affect of Varying Salt Concentrations on the Stability of
Adipocyte Lipid-Binding Protein
Adipocyte lipid binding protein (ALBP) is a 14.6kDa intracellular
protein found in adipocytes. According to crystallographic studies,
the protein has a positively charged internal, water-filled
cavity that binds fatty acids and a “portal” that
connects the cavity of the protein to the external solvent.
The polarized surface of the molecule suggested that it should
be dramatically influenced by the ions in solution. This has
been shown to be the case in previous experiments in this laboratory:
ALBP was stabilized by the addition of potassium chloride (KCl)
in urea denaturations. However, it is not certain which ions
of KCl (potassium, chloride or both) are the main stabilizers
of the protein. To attempt to answer this question, guanidine
hydrochloride (GdnHCl) denaturations of ALBP with varying concentrations
of added KCl (0 to 0.5M) were carried out. In GdnHCl, the ?G
of unfolding decreased by 1.272kcal/mol with increasing KCl
concentrations up to 500mM. This decrease indicates that the
protein was destabilized, which was attributed to the abundance
of chloride ions in solution (from both the GdnHCl and the KCl).
Urea denaturations of ALBP with choline chloride (CholCl) were
then performed in order to confirm if this destabilizing effect
was due to the presence of chloride ions. Choline is a bulky
cation that cannot bind to proteins because of its size, meaning
that the only ion affecting the denaturations would be chloride.
Preliminary results suggest that the protein again undergoes
destabilization, as the denaturation at 500mM CholCl resulted
in a decrease in ?G by 3.499kcal/mol.
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