Modifying the substrate specificity of carcinoscorpius rotundicauda serine protease inhibitor domain 1 to target thrombin

Pankaj Kumar Giri, Xuhua Tang, Saravanan Thangamani, Rajesh T. Shenoy, Jeak Ling Ding, Kunchithapadam Swaminathan, J. Sivaraman

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Protease inhibitors play a decisive role in maintaining homeostasis and eliciting antimicrobial activities. Invertebrates like the horseshoe crab have developed unique modalities with serine protease inhibitors to detect and respond to microbial and host proteases. Two isoforms of an immunomodulatory two-domain Kazal-like serine protease inhibitor, CrSPI-1 and CrSPI-2, have been recently identified in the hepatopancreas of the horseshoe crab, Carcinoscorpius rotundicauda. Full length and domain 2 of CrSPI-1 display powerful inhibitory activities against subtilisin. However, the structure and function of CrSPI-1 domain-1 (D1) remain unknown. Here, we report the crystal structure of CrSPI-1-D1 refined up to 2.0 A resolution. Despite the close structural homology of CrSPI-1-D1 to rhodniin-D1 (a known thrombin inhibitor), the CrSPI-1-D1 does not inhibit thrombin. This prompted us to modify the selectivity of CrSPI-1-D1 specifically towards thrombin. We illustrate the use of structural information of CrSPI-1-D1 to modify this domain into a potent thrombin inhibitor with IC50 of 26.3 nM. In addition, these studies demonstrate that, besides the rigid conformation of the reactive site loop of the inhibitor, the sequence is the most important determinant of the specificity of the inhibitor. This study will lead to the significant application to modify a multi-domain inhibitor protein to target several proteases.

Original languageEnglish (US)
Article numbere15258
JournalPloS one
Issue number12
StatePublished - 2010
Externally publishedYes

ASJC Scopus subject areas

  • General


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