A, a ribbon drawing of a dimeric TSPN-1, in which two monomers are related by a pseudo 2-fold rotation axis. Residue Arg-42 from the major heparin-binding site at the bottom of each domain is drawn in ball-and-stick form. The two TSPN-1 domains contact each other to form a small hydrophobic interface contributed mainly by residues on the β2_β3 loop, including Leu-30, Pro-36, Ser-37, and Pro-39. The electric dipole moment of the dimeric TSPN-1 is shown by the blue arrow and centered at the beginning of the arrow. B, an electrostatic potential surface representation of the dimeric TSPN-1. The dimeric TSPN-1 forms an extended positively charged patch (~20×60Ų) by bridging the major heparin-binding sites of two TSPN-1 domains. The orientation of the figure is related to the position of the dimeric TSPN-1 in panel A by a rotation of ~90° around the horizontal axis. Some extra bulky electron densities associated with the extended positively charged patch are located in the positions marked by yellow crosses. They were assigned to SO₄ groups from dp10 and presumed to provide gluing points between TSPN-1 and dp10. C, the major heparin-binding site of TSPN-1 domain A with a 2F_o – F_c map contoured at the 1.3σ. The map is colored in blue. The two SO₄ groups associated with residue Arg-42 are also seen in the TSPN-1·Arixtra complex structure (15). For refinement purposes, several water molecules, as shown in pink crosses, were positioned into the uncharacterized continuous densities from these SO₄ groups. Figs. 1A, 2A, 3A, 4A, and 5A were prepared using the program MolScript (50), Figs. 1B, 3B, and 5B were prepared using the program GRASP (28). Figs. 1C and 3C were prepared using the program COOT (51).

A, a ribbon drawing of a dimeric TSPN-1, in which two monomers are related by a symmetric 2-fold rotation axis. Residue Arg-42 from the major heparin-binding site of each domain is drawn in ball-and-stick form. The two TSPN-1 domains contact each other to form a small hydrophobic interface contributed mainly by residues on the β2_β3 loop, including Leu-30 and Val-31. The electric dipole moment of the dimeric TSPN-1 is shown by the blue arrow and centered at the beginning of the arrow. B, an electrostatic potential surface representation of the dimeric TSPN-1. The dimeric TSPN-1 forms an extended positively charged shallow groove (~30 Å long) by bridging the juxtaposing major heparin-binding sites of two TSPN-1 domains. The orientation of the figure is similar to the position of the dimeric TSPN-1 in panel A. C, the major heparin-binding site of TSPN-1 with a 2F_o – F_c map contoured at the 0.9σ. The map is colored in blue. For refinement purpose, a water molecule, as shown with a pink cross, has been positioned into the uncharacterized continuous densities around the positively charged residues.

A, a ribbon drawing of the two TSPN-1 domains in one asymmetric unit. They are not related by any pseudo-symmetric operation. Residue Arg-42 from the major heparin-binding site of each domain is drawn in ball-and-stick form. The two TSPN-1 domains interact with each other extensively through their edge strands (see “Results”). The electric dipole moment of the two TSPN-1 domains is shown by the blue arrow and centered at the beginning of the arrow. B, an electrostatic potential surface representation of thetwoTSPN-1domainsin the nativeTSPN-1structure. Residue Arg-42 from the major heparin-binding site of each TSPN-1 domain is labeled to show the separation of the two major heparin-binding sites in this native structure. The orientation of the figure is similar to the one shown in panel A.

A, TSPN-1·dp10 low energy complex identified using AutoDock4. TSPN-1 residues involved in the hydrogen bonding network are rendered in ball-and-stick. Each residue involved in the hydrogen bonding network is annotated. For clarity hydrogen bonds are not displayed. Each domain is labeled and rendered as a ribbon drawing, with α-helices colored green (domain A) or magenta (domain B), and β-strands and random coil are colored cyan (domain A) or yellow (domain B). The heparin moiety dp10 is rendered in ball and stick representation. B, Molcad surface of the TSPN-1·dp10 complex with residues involved in the hydrogen bonding network colored in blue. This view of the TSPN-1·dp10 complex is the result of rotating the complex −90° around the x-axis (out of the plane of the page or screen) to provide a view of this complex from the heparin binding site, which is located at the base of complex in panel A. Figs. 2B and 4B were prepared using the SYBYL suite of programs (Tripos).

A, TSPN-1·dp8 low energy complex identified using AutoDock4. TSPN-1 residues involved in the hydrogen bonding network are rendered in ball-and-stick and annotated to identify those residues involved in the hydrogen bonding network. For clarity hydrogen bonds are not displayed. Each domain is labeled and rendered as a ribbon drawing, with α-helices colored green (domain A) or magenta (domain B), and β-strands and random coil colored cyan (domain A) or yellow (domain B). The heparin moiety dp8 is rendered in ball and stick. B, Molcad surface of the TSPN-1·dp8 complex with residues involved in the hydrogen bonding network colored blue. The TSPN-1·dp8 complex in panel B has been rotated 90° around the x-axis and 45° around the y-axis (out of the plane of the page or screen) to provide a view of this complex from the heparin binding site at the top of the complex as illustrated in A.