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Figure 2.
FIG. 2. Schematic of observed contacts between the two
heparin chains and the four thrombin monomers of the asymmetric
unit. Six heparin monosaccharide units were built into the
electron density between monomers AB and GH (A), and five were
built between monomers CD and EF (B). In both dimers, monomers
in equivalent positions (AB and CD) make them most intimate
contacts with heparin, with minimal contacts observed between
heparin and the other pair of equivalent monomers (EF and GH,
see Fig. 1A). All contacts are between heparin and atoms on the
side chains of indicated thrombin residues, with the exception
of a main chain hydrogen bond for Trp237 (dotted line). The line
style denotes the type of interaction: with a solid line
indicating a salt bridge, a dashed line indicating a hydrogen
bond, a dotted-dashed line indicating a water-mediated hydrogen
bond, and a jagged dotted line indicating potential ionic
interactions for incompletely built side chains. The packing of
the monomers against one another placed Lys236 into close
approximation with the same residue of the dimer partner,
resulting in its disorder in the crystal structure.
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