The solution structure of the recombinant tick anticoagulant protein (rTAP) was determined by 1H nuclear magnetic resonance (NMR) spectroscopy in aqueous solution at pH 3.6 and 36°C. rTAP is a 60-residue protein functioning as a highly specific inhibitor of the coagulation protease factor Xa, which was originally isolated from the tick Ornithodoros moubata. Its regular secondary structure consists of a two-stranded antiparallel β-sheet with residues 22-28 and 32-38, and an α-helix with residues 51-60. The relative orientation of these regular secondary structure elements has nearly identical counterparts in the bovine pancreatic trypsin inhibitor (BPTI). In contrast, the loop between the β-sheet and the C-terminal α-helix as well as the N-terminal 20-residue segment preceding the β-sheet adopt different three-dimensional folds in the two proteins. These observations are discussed with regard to the implication of different mechanisms of protease inhibition by rTAP and by Kunitz-type protein proteinase inhibitors. © 1994.
Antuch, W., Güntert, P., Billeter, M., Hawthorne, T., Grossenbacher, H., & Wüthrich, K. (1994). NMR solution structure of the recombinant tick anticoagulant protein (rTAP), a factor Xa inhibitor from the tick Ornithodoros moubata. FEBS Letters, 352(2), 251–257. https://doi.org/10.1016/0014-5793(94)00941-4