3QTL

Structural Basis for Dual-inhibition Mechanism of a Non-classical Kazal-type Serine Protease Inhibitor from Horseshoe Crab in Complex with Subtilisin

Summary for 3QTL

• Entry DOI: 10.2210/pdb3qtl/pdb
• Descriptor: Subtilisin-like serin protease, Kazal-type serine protease inhibitor SPI-1 (3 entities in total)
• Functional Keywords: serine protease -kazal type serine protease inhibitor complex, hydrolase inhibitor, hydrolase-hydrolase inhibitor complex, hydrolase/hydrolase inhibitor
• Biological source: Bacillus licheniformis; More
• Total number of polymer chains: 4
• Total formula weight: 90229.96

Authors

Shenoy, R.T.,Sivaraman, J. (deposition date: 2011-02-23, release date: 2011-06-01, Last modification date: 2024-11-20)

Primary citation

Shenoy, R.T.,Thangamani, S.,Velazquez-Campoy, A.,Ho, B.,Ding, J.L.,Sivaraman, J.
Structural basis for dual-inhibition mechanism of a non-classical kazal-type serine protease inhibitor from horseshoe crab in complex with subtilisin.
Plos One, 6:e18838-e18838, 2011

PubMed Abstract: Serine proteases play a crucial role in host-pathogen interactions. In the innate immune system of invertebrates, multi-domain protease inhibitors are important for the regulation of host-pathogen interactions and antimicrobial activities. Serine protease inhibitors, 9.3-kDa CrSPI isoforms 1 and 2, have been identified from the hepatopancreas of the horseshoe crab, Carcinoscorpius rotundicauda. The CrSPIs were biochemically active, especially CrSPI-1, which potently inhibited subtilisin (Ki = 1.43 nM). CrSPI has been grouped with the non-classical Kazal-type inhibitors due to its unusual cysteine distribution. Here we report the crystal structure of CrSPI-1 in complex with subtilisin at 2.6 Å resolution and the results of biophysical interaction studies. The CrSPI-1 molecule has two domains arranged in an extended conformation. These two domains act as heads that independently interact with two separate subtilisin molecules, resulting in the inhibition of subtilisin activity at a ratio of 1:2 (inhibitor to protease). Each subtilisin molecule interacts with the reactive site loop from each domain of CrSPI-1 through a standard canonical binding mode and forms a single ternary complex. In addition, we propose the substrate preferences of each domain of CrSPI-1. Domain 2 is specific towards the bacterial protease subtilisin, while domain 1 is likely to interact with the host protease, Furin. Elucidation of the structure of the CrSPI-1: subtilisin (1∶2) ternary complex increases our understanding of host-pathogen interactions in the innate immune system at the molecular level and provides new strategies for immunomodulation.

PubMed: 21541315
DOI: 10.1371/journal.pone.0018838

Experimental method

X-RAY DIFFRACTION (2.6 Å)