Structural Determinants of the Bifunctional Corn Hageman Factor Inhibitor:  X-ray Crystal Structure at 1.95 Å Resolution

• Published in: Biochemistry (Easton) 1998-11, Vol.37 (44), p.15277-15288
• Main Authors: Behnke, Craig A, Yee, Vivien C, Trong, Isolde Le, Pedersen, Lars C, Stenkamp, Ronald E, Kim, Seung-Sup, Reeck, Gerald R, Teller, David C
• Format: Article
• Language: English
• Subjects: alpha-Amylases - antagonists & inhibitors; alpha-Amylases - metabolism; Amino Acid Sequence; Computer Simulation; Conserved Sequence; Crystallization; Crystallography, X-Ray; Factor XIIa - antagonists & inhibitors; Humans; Models, Molecular; Molecular Sequence Data; Plant Proteins - chemistry; Protein Structure, Secondary; Sequence Alignment; Sequence Analysis; Sequence Homology, Amino Acid; Serine Proteinase Inhibitors - chemistry; Trypsin Inhibitors - chemistry; Zea mays - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi9812266

Corn Hageman factor inhibitor (CHFI) is a bifunctional 127 residue, 13.6 kDa protein isolated from corn seeds. It inhibits mammalian trypsin and Factor XIIa (Hageman Factor) of the contact pathway of coagulation as well as α-amylases from several insect species. Among the plasma proteinases, CHFI specifically inhibits Factor XIIa without affecting the activity of other coagulation proteinases. We have isolated CHFI from corn and determined the crystallographic structure at 1.95 Å resolution. Additionally, we have solved the structure of the recombinant protein produced in Escherichia coli at 2.2 Å resolution. The two proteins are essentially identical. The proteinase binding loop is in the canonical conformation for proteinase inhibitors. In an effort to understand α-amylase inhibition by members of the family of 25 cereal trypsin/α-amylase inhibitors, we have made three-dimensional models of several proteins in the family based on the CHFI coordinates and the coordinates determined for wheat α-amylase inhibitor 0.19 [Oda, Y., Matsunaga, T., Fukuyama, K., Miyazaki, T., and Morimoto, T. (1997) Biochemistry 36, 13503−13511]. From an analysis of the models and a structure-based sequence analysis, we propose a testable hypothesis for the regions of these proteins which bind α-amylase. In the course of the investigations, we have found that the cereal trypsin/α-amylase inhibitor family is evolutionarily related to the family of nonspecific lipid-transfer proteins of plants. This is a new addition to the group which now consists of the trypsin/α-amylase inhibitors, 2S seed storage albumins, and the lipid-transfer family. Apparently, the four-helix conformation has been a successful vehicle in plant evolution for providing protection from predators, food for the embryo, and lipid transfer.