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Abstract
Kunitz-type trypsin inhibitors bind to the active pocket of trypsin causing its inhibition. Plant Kunitz-type inhibitors are thought to be important in defense, especially against insect pests. From sequence analysis of various Kunitz-type inhibitors from plants, we identified CaTI2 from chickpea as a unique variant lacking the functionally important arginine residue corresponding to the soybean trypsin inhibitor (STI) and having a distinct and unique inhibitory loop organization. To further explore the implications of these sequence variations, we obtained the crystal structure of recombinant CaTI2 at 2.8Å resolution. It is evident from the structure that the variations in the inhibitory loop facilitates non-substrate like binding of CaTI2 to trypsin, while the canonical inhibitor STI binds to trypsin in substrate like manner. Our results establish the unique mechanism of trypsin inhibition by CaTI2, which warrant further research into its substrate spectrum.
| Abbreviations | ||
| BApNA | = | Nα-Benzoyl-L-arginine 4-nitroanilide |
| BPT | = | bovine pancreatic trypsin |
| CaTI2 | = | Cicer arietinum L trypsin inhibitor 2 |
| DrTI | = | Delonix regia Trypsin inhibitor |
| EcTI | = | Enterolobium contortisiliquum trypsin inhibitor |
| ETI | = | Erythrina caffra trypsin inhibitor |
| KTI | = | Kunitz type inhibitor |
| STI | = | soybean trypsin inhibitor |
| TKI | = | Tamarindus indica Kunitz inhibitor |
Communicated By Ramaswamy H. Sarma
Acknowledgments
ADB thanks University Grant Commission, India for Research Fellowship. SKR thanks Department of Science and Technology, India for Ramanujan Fellowship. The authors thank Dr Ravindra Makde and Dr Ashwani Kumar from PX-BL21 beamline (BARC) at Indus-2, RRCAT, Indore (India) for synchrotron facility. A word of thanks also goes to Dr Sivaramaiah Nallapeta and Dr Saji Menon from NanoTemper Technologies, India for providing MST facilities.
Disclosure statement
The authors certify that there is no actual or potential conflict of interest in relation to this article.