The binding of small volatile molecules by bovine [beta]-lactoglobulin : a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University
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Date
2008
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Massey University
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Abstract
Bovine ß-lactoglobulin (ß-Lg) has been studied extensively but there is no
clear identification of its biological function. Hydrophobic molecules have been
observed binding into the hydrophobic calyx of ß-Lg. By comparison with other
members of lipocalin family, it is probable that ß-Lg plays a role of transport of
ligands, as ligands also bind into the central cavity of lipocalins. The
structurally similar MUP is a pheromone-binding protein; therefore, it is
possible that ß-Lg may also fulfil a similar role. This study has begun to test
this hypothesis by investigating the interactions between bovine ß-Lg and
several small volatile molecules (2-sec-4,5-dihydrothiazole, 3-methyl-2-butenal,
3-methyl-2-buten-1-ol and phenylacetic acid). The interactions between the
volatile molecules and ß-Lg were studied by both two-dimensional NMR
spectroscopy and X-ray crystallographic methods. TOCSY spectra were
recorded for ß-Lg and the complex between ß-Lg and the ligands. The
observed chemical shifts in the HN-Ha region are sensitive to the proximity of
ligands, and hence chemical shift changes on ligand binding provide
information on possible binding sites. It appears that several amino acids with
hydrophobic sidechains are affected by interaction with volatile molecules at
pH 2.0. The X-ray crystallographic study at pH 8.5 showed that the potential
ligand, 2-sec-4,5-dihydrothiazole, may have decomposed into a linear
2-methyl-butanol. The refined structure (R=0.281, Rfree=0.354 for reflections to
2.6 Å resolution) reveals that the potential ligand may bind to the central cavity
in a manner similar to the binding of 12-bromodecanoic acid to ß-Lg.
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Keywords
Bovine [beta]-lactoglobulin, Molecular biology