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Figure 1.
Figure 1. Structure of the I222 streptavidin-biotin
tetramer, pH 2.00, showing the strong and weak intersubunit
interfaces. The β-strands are colored yellow, the loop bearing
Asp61 purple, the flexible flap that interacts with biotin
green, the loop bearing Arg84 dark blue, and the remaining
loops cyan. The Trp120 side-chain that interacts with biotin at
the weak interface is shown. The His87 and Asp61 side-chains at
the strong interface are shown in conformations associated with
the intersubunit hydrogen-bonded salt bridge. Interloop hydrogen
bonds involving Arg84, Glu51, and Asn49 are shown.
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