TY - JOUR
T1 - Crystal Structure of Cellular Retinoic Acid Binding Protein I Shows Increased Access to the Binding Cavity due to Formation of an Intermolecular Β-Sheet
AU - Thompson, James R.
AU - Bratt, Judy M.
AU - Banaszak, Leonard J.
N1 - Funding Information:
We are grateful to Dr Ellen Li at Washington University for providing us with the strain of E. coli containing the expression plasmid for murine CRABPI. The authors thank Ed Hoeffner for maintaining the X-ray diffraction instrumentation, and the computing hardware and software. We thank Jeremia Ory and Bob Ledford for help in protein purification. We also gratefully acknowledge research support from the NIH (GM 13925) and the Minnesota Supercomputer Institute.
PY - 1995/9/29
Y1 - 1995/9/29
N2 - A recombinant form of murine apo-cellular retinoic acid binding protein I (apo-CRABPI) has been purified and crystallized at pH 5.0, and the crystal structure has been refined to anR-factor of 19.6% at a resolution of 2.7 Å. CRABPI binds all-transretinoic acid and some retinoic acid metabolites with nanomolar affinities. Coordinates of the holo form of CRABP were not available during the early stages of the study, and in spite of numerous homologs of known structure, phases were not obtainable through molecular replacement. Instead, an interpretable electron density map was obtained by multple isomorphous replacement methods after improvement of the heavy-atom parameters with density modified trial phases. Two molecules of apo-CRABPI occupy theP3121 asymmetric unit and are related by pseudo 2-fold rotational symmetry. Unique conformational differences are apparent between the two molecules. IN all of the family members studied to date, there is a lack of hydrogen bonds between two of the component β-strands resulting in a gap in the interstand hydrogen bonding pattern. In the crystallographic dimer described here, a continuous intermolecular β-sheet is formed by using this gap region. This is possible because of an 8 Å outward maximum displacement of the tight turn between the third and fourth β-strands on one of the molecules. The result is a double β-barrel containing two apo-CRABPI molecules with a more open, ligand-accessible binding cavity, which has not been observed in other structures of a family of proteins that bind hydrophobic ligands.
AB - A recombinant form of murine apo-cellular retinoic acid binding protein I (apo-CRABPI) has been purified and crystallized at pH 5.0, and the crystal structure has been refined to anR-factor of 19.6% at a resolution of 2.7 Å. CRABPI binds all-transretinoic acid and some retinoic acid metabolites with nanomolar affinities. Coordinates of the holo form of CRABP were not available during the early stages of the study, and in spite of numerous homologs of known structure, phases were not obtainable through molecular replacement. Instead, an interpretable electron density map was obtained by multple isomorphous replacement methods after improvement of the heavy-atom parameters with density modified trial phases. Two molecules of apo-CRABPI occupy theP3121 asymmetric unit and are related by pseudo 2-fold rotational symmetry. Unique conformational differences are apparent between the two molecules. IN all of the family members studied to date, there is a lack of hydrogen bonds between two of the component β-strands resulting in a gap in the interstand hydrogen bonding pattern. In the crystallographic dimer described here, a continuous intermolecular β-sheet is formed by using this gap region. This is possible because of an 8 Å outward maximum displacement of the tight turn between the third and fourth β-strands on one of the molecules. The result is a double β-barrel containing two apo-CRABPI molecules with a more open, ligand-accessible binding cavity, which has not been observed in other structures of a family of proteins that bind hydrophobic ligands.
KW - CRABPI
KW - Cellular retinoic acid binding protein I
KW - Lipid binding protein
KW - Retinoic acid
KW - Vitamin A
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U2 - 10.1006/jmbi.1995.0509
DO - 10.1006/jmbi.1995.0509
M3 - Article
C2 - 7563063
AN - SCOPUS:0029125852
SN - 0022-2836
VL - 252
SP - 433
EP - 446
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 4
ER -