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Figure 1.
Figure 1 Solid-surface representation of the tryptase
tetramer. The colours indicate positive (blue) and negative
(red) electrostatic potential at the molecular surface. Figures
made with GRASP28. a, Front view. The four monomers (labelled A
to D) are arranged at the corners of a flat square. Horizontal
and vertical local two-fold symmetry axes, relating monomer A
(or D) with B (or C), and monomer A (or B) with D (or C),
respectively, run through the tetramer centre, as does a third,
perpendicular, axis. The four monomers leave a central pore. Two
of the four bound APPA molecules (yellow) are visible, whereas
the two others are shielded by projecting flaps. The (blue)
patches of positively charged residues at the surfaces of
monomers B and D extend towards the A-B and C-D peripheries. b,
Edge view towards the C-D dimer. The tetramer has been rotated
around a vertical axis by almost 90° compared with a, clearing
the view towards the peripheral sides of monomers C (bottom) and
D (top). The positively charged patches on both monomers extend
towards the front side (right) of D and the back side (left) of
C. An extended heparin chain of almost 100 ? could span both
patches, strengthening the small C-D and A-B contacts.
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