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Conformational changes of ovine α-1-proteinase inhibitor: The influence of heparin binding.

Vivek Kumar, Gupta and Lalitha, R. Gowda (2008) Conformational changes of ovine α-1-proteinase inhibitor: The influence of heparin binding. Journal of Molecular Structure, 891 (1-3). 456-462 .

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α-1-Proteinase inhibitor (α-1-PI), the archetypal serpin causes rapid, irreversible stoichiometric inhibition of redundant circulating serine proteases and is associated with emphysema, inflammatory response and maintenance of protease-inhibitor equilibrium in vascular and peri-vascular spaces. A homogenous preparation of heparin octasaccharide binds to ovine and human α-1-PI and enhances their protease inhibitory activity phenomenally. Size-exclusion chromatography and dynamic light scattering experiments reveal that ovine α-1-PI undergoes a decrease in the Stokes’ radius upon heparin binding. A strong binding; characterizes this α-1-PI–heparin interaction as revealed by the binding constant (Kα) 1.98 ± 0.2 × 10−6 M and 2.1 ± 0.2 × 10−6 M determined by fluorescence spectroscopy and equilibrium dialysis, respectively. The stoichiometry of heparin binding to ovine α-1-PI was 1.1 ± 0.2:1. The Stern–Volmer constants (Ksv) for heparin activated ovine and human α-1-PI were found to be 5.13 × 10−6 M and 5.67 × 10−6 M, respectively, significantly higher than the native inhibitors. FTIR and CD spectroscopy project the systematic structural reorientations that α-1-PI undergoes upon heparin binding characterized by a decrease in α-helical content and a concomitant increase in β-turn and random coil elements. It is likely that these conformational changes result in the movement of the α-1-PI reactive site loop into an extended structure that is better poised to combat the cognate protease and accelerate the inhibition.

Item Type: Article
Uncontrolled Keywords: Dynamic light scattering; Hydrodynamic radius; Equilibrium dialysis; Fluorescence spectroscopy; Fourier transform infra-red spectroscopy; Circular dichroism
Subjects: 500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 29 Protein Chemistry
Divisions: Protein Chemistry and Technology
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 09 Aug 2011 05:43
Last Modified: 09 Aug 2011 05:43
URI: http://ir.cftri.res.in/id/eprint/10431

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