Indicative of a protease inhibitor, usually a serine protease inhibitor. Structure is a disulfide rich alpha+beta fold. BPTI (bovine pancreatic trypsin inhibitor) is an extensively studied model structure. Certain family members are similar to the tick anticoagulant peptide (TAP, Swiss:P17726). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways [1]. TAP molecules are highly dipolar [2], and are arranged to form a twisted two- stranded antiparallel beta-sheet followed by an alpha helix [1].

1: NMR solution structure of the recombinant tick anticoagulant protein (rTAP), a factor Xa inhibitor from the tick Ornithodoros moubata. Antuch W, Guntert P, Billeter M, Hawthorne T, Grossenbacher H, Wuthrich K; FEBS Lett 1994;352:251-257. PMID:7925983

2: Structure of tick anticoagulant peptide at 1.6 A resolution complexed with bovine pancreatic trypsin inhibitor. St Charles R, Padmanabhan K, Arni RV, Padmanabhan KP, Tulinsky A; Protein Sci 2000;9:265-272. PMID:10716178