Identification of the Factor VIIa Binding Site on Tissue Factor by Homologous Loop Swap and Alanine Scanning Mutagenesis

• Published in: Biochemistry (Easton) Vol. 33; no. 47; pp. 14003 - 14010
• Main Authors: Gibbs, Craig S, McCurdy, Sarah N, Leung, Lawrence L. K, Paborsky, Lisa R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.11.1994
• Subjects: Alanine - genetics; Amino Acid Sequence; Binding Sites; Electrophoresis, Polyacrylamide Gel; Enzyme-Linked Immunosorbent Assay; Escherichia coli - genetics; Factor VIIa - metabolism; Interferon-gamma; Models, Molecular; Molecular Sequence Data; Molecular Structure; Mutagenesis, Site-Directed; Protein Conformation; Receptors, Interferon - chemistry; Receptors, Interferon - genetics; Recombinant Proteins - isolation & purification; Sequence Alignment; Structure-Activity Relationship; Thromboplastin - chemistry; Thromboplastin - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00251a007

Tissue factor (TF) is a membrane-bound glycoprotein that functions as a cofactor for coagulation factor VIIa (VIIa) and initiates blood coagulation at sites of vascular injury. On the basis of sequence alignments, TF was predicted to be a member of the cytokine receptor superfamily. Utilizing the structural information available for the cytokine receptor superfamily, we have used site-directed mutagenesis to identify the binding site on TF for VIIa. The predicted loop regions in TF were systematically replaced with the homologous loops from the gamma-interferon receptor (gamma-IFN-R), the protein most related to TF in the superfamily of cytokine receptors. Six discontinuous regions (residues 16-20, 40-46, 60-69, 101-111, 129-151, 193-207) were identified that are required for interaction with VIIa and enhancement of activity. Individual substitution of 68 residues within these loops with alanine revealed eight residues (K20, D44, W45, K46, Q110, R135, F140, V207) that are required for cofactor activity. These residues fall into two groups, those that are required only for interactions with VIIa (K46, Q110, R135, F140, V207) and those that are also required to induce the conformational change in VIIa required for enhanced activity (K20, D44, W45). The discontinuous regions of TF required for interactions with VIIa form a single binding surface for VIIa that is analogous to the interface defined by the crystal structure of the complex between growth hormone and its receptor.