W. Ruf et al., ENERGETIC CONTRIBUTIONS AND TOPOGRAPHICAL ORGANIZATION OF LIGAND-BINDING RESIDUES OF TISSUE FACTOR, Biochemistry, 34(19), 1995, pp. 6310-6315
Tissue factor is the cellular receptor and macromolecular enzymatic co
factor for the serine protease coagulation factor VIIa. The ligand bin
ding extracellular domain of tissue factor consists of two structural
modules which fold similar to fibronectin type III modules, consistent
with the classification of tissue factor as a member of the class 2 c
ytokine receptor family. On the basis of the three-dimensional structu
re, we here analyze the importance of tissue factor residues for bindi
ng of ligand by scanning alanine mutagenesis. The identified significa
nt binding contacts account for as much as 80% of the calculated total
free energy of ligand binding. Most residues with energetic contribut
ions to ligand binding are well exposed to solvent, and the area for l
igand interaction extends from the cleft formed by the two structural
modules (residues Lys(20), Ile(22), Lys(48), Asp(58), Arg(135), Phe(14
0)) to the convex-shaped edge of the three- and four-stranded sheets c
haracterized by a patch of surface-exposed hydrophobic side chains in
the amino-terminal module (residues Gln(37), Asp(44), Trp(45), Phe(76)
, Tyr(78)), The binding residues are dispersed over an extended surfac
e area, indicating adaptation to the recognition of specific structura
l modules of the macromolecular ligand factor VIIa. This analysis prov
ides detailed insight into the three-dimensional organization of the l
igand docking structure of the initiating cofactor for the coagulation
pathways.