Standalone Kunitz domains are used as a framework for the development of new pharmaceutical drugs.[2]
Structure
The structure is a disulfide rich alpha+beta fold. Bovine pancreatic trypsin inhibitor is an extensively studied model structure. Certain family members are similar to the tick anticoagulant peptide (TAP, P17726). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways.[3] TAP molecules are highly dipolar,[4] and are arranged to form a twisted two-stranded antiparallel beta sheet followed by an alpha helix.[3]
The majority of the sequences having this domain belong to the MEROPS inhibitor family I2, clan IB; the Kunitz/bovine pancreatic trypsin inhibitor family, they inhibit proteases of the S1 family[5] and are restricted to the metazoa with a single exception: Amsacta moorei entomopoxvirus, a species of poxvirus. They are short (about 50 to 60 amino acid residues) alpha/beta proteins with few secondary structures. The fold is constrained by three disulfide bonds. The type example for this family is BPTI[6] (or basic protease inhibitor), but the family includes numerous other members,[7][8][9][10] such as snake venom basic protease; mammalian inter-alpha-trypsin inhibitors; trypstatin, a rat mast cell inhibitor of trypsin; a domain found in an alternatively spliced form of Alzheimer's amyloid beta-protein; domains at the C-termini of the alpha-1 and alpha-3 chains of type VI and type VII collagens; tissue factor pathway inhibitor precursor; and Kunitz STI protease inhibitor contained in legume seeds.
Drug development
Kunitz domains are stable as standalone peptides, able to recognise specific protein structures, and also work as competitive protease inhibitors in their free form. These properties have led to attempts at developing biopharmaceutical drugs from Kunitz domains. Candidate domains are selected from molecular libraries containing over 10 million variants with the aid of display techniques like phage display,[11] and can be produced in large scale by genetically engineered organisms.
^PDB: 1KTH; Arnoux B, Ducruix A, Prangé T (July 2002). "Anisotropic behaviour of the C-terminal Kunitz-type domain of the alpha3 chain of human type VI collagen at atomic resolution (0.9 Å)". Acta Crystallogr. D. 58 (Pt 7): 1252–4. doi:10.1107/S0907444902007333. PMID12077460.
^Nixon, AE; Wood, CR (2006). "Engineered protein inhibitors of proteases". Current Opinion in Drug Discovery & Development. 9 (2): 261–8. PMID16566296.
^Wlodawer A, Housset D, Kim KS, Fuchs J, Woodward C (1991). "Crystal structure of a Y35G mutant of bovine pancreatic trypsin inhibitor". J. Mol. Biol. 220 (3): 757–770. doi:10.1016/0022-2836(91)90115-M. PMID1714504.
^Salier JP (1990). "Inter-alpha-trypsin inhibitor: emergence of a family within the Kunitz-type protease inhibitor superfamily". Trends Biochem. Sci. 15 (11): 435–439. doi:10.1016/0968-0004(90)90282-G. PMID1703675.
^Takahashi K, Ikeo K, Gojobori T (1992). "Evolutionary origin of a Kunitz-type trypsin inhibitor domain inserted in the amyloid beta precursor protein of Alzheimer's disease". J. Mol. Evol. 34 (6): 536–543. doi:10.1007/BF00160466. PMID1593645. S2CID26698630.
^ abLehmann, A (2008). "Ecallantide (DX-88), a plasma kallikrein inhibitor for the treatment of hereditary angioedema and the prevention of blood loss in on-pump cardiothoracic surgery". Expert Opinion on Biological Therapy. 8 (8): 1187–99. doi:10.1517/14712598.8.8.1187. PMID18613770. S2CID72623604.
^Clinical trial number NCT00455767 for "Safety and Efficacy Study of Depelestat in Acute Respiratory Distress Syndrome (ARDS) Patients" at ClinicalTrials.gov
^Attucci, S; Gauthier, A; Korkmaz, B; Delépine, P; Martino, MF; Saudubray, F; Diot, P; Gauthier, F (2006). "EPI-hNE4, a proteolysis-resistant inhibitor of human neutrophil elastase and potential anti-inflammatory drug for treating cystic fibrosis". The Journal of Pharmacology and Experimental Therapeutics. 318 (2): 803–9. doi:10.1124/jpet.106.103440. PMID16627747. S2CID1771342.
