Journal
ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY
Volume 67, Issue -, Pages 813-821Publisher
WILEY-BLACKWELL
DOI: 10.1107/S0907444911027806
Keywords
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Funding
- Department of Energy, Office of Biological and Environmental Research
- National Institutes of Health, National Center for Research Resources
- National Institute of General Medical Sciences
- National Institutes of Health [GM080214]
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Atomic resolution crystallographic studies of streptavidin and its biotin complex have been carried out at 1.03 and 0.95 angstrom, respectively. The wild-type protein crystallized with a tetramer in the asymmetric unit, while the crystals of the biotin complex contained two subunits in the asymmetric unit. Comparison of the six subunits shows the various ways in which the protein accommodates ligand binding and different crystal-packing environments. Conformational variation is found in each of the polypeptide loops connecting the eight strands in the beta-sandwich subunit, but the largest differences are found in the flexible binding loop (residues 45-52). In three of the unliganded subunits the loop is in an 'open' conformation, while in the two subunits binding biotin, as well as in one of the unliganded subunits, this loop 'closes' over the biotin-binding site. The 'closed' loop contributes to the protein's high affinity for biotin. Analysis of the anisotropic displacement parameters included in the crystallographic models is consistent with the variation found in the loop structures and the view that the dynamic nature of the protein structure contributes to the ability of the protein to bind biotin so tightly.
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