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Title: Structural studies on β-lactoglobulin and cyclophilin 3
Author: Wu, Su-Ying
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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The structures of BLG in three space groups have been solved. However, the refinement of the lattice Y structure has shown problematic. In the current study, a new data set has been collected at low temperature (100K) and the structure has been refined to 2.0A with the R-factor of 25.7% (Rfree=31.0%). The R-factor remains around 26% although many methods have been tried to lower it. The possible reasons that hinder the successful refinement are discussed. In common with many of the other members of the lipocalin family, BLG binds a variety of hydrophobic ligands. It appears possible that there are two distinct binding sites per monomer. By comparison with other members of the family, there is a probable binding site in the central calyx of the protein formed by the eight antiparallel b-strands. In this thesis, cocrystallization of BLG with palmitate has been successful and the structure of palmitate-bound BLG has been solved and refined at a resolution of 2.5A to an R-factor of 20.4% (Rfree = 24%). The clear electron density map shows the ligand binds inside the calyx and lies parallel to b-strand E. The palmitate adopts an almost fully extended conformation with the hydrophobic tail stretching into the bottom of the calyx. The carboxyl group of palmitate forms two hydrogen binds with Lys60 and Lys69 at the entrance of the calyx. This the first direct observation of a ligand binding to BLG. The structure of CYP3 has been refined to 1.8A with R-factor of 20.8% (Rfree = 28.4%). The structure is similar to the well-characterised human cyclophilin A. It contains a eight-stranded antiparallel b-barrel, similar to, but distinct from, BLG, capped with two a-helices. However, CYP3 has an additional loop composed of seven residues (48KSGKPLH54), which is absent in CYPA. This loop is held tightly by a specific network of hydrogen bonds from the side chain of Glu83. The biological role of this additional loop is still unclear although it may provide a distinctive recognition feature of the C. elegans -cyclophilin family as this inserted loop is particularly common in this family.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available