Structural Insights of the Cysteine Protease Heynein from Induction and Characterization of Non-native Intermediate States

Patel, Basant Kumar and Medicherla, V J (2010) Structural Insights of the Cysteine Protease Heynein from Induction and Characterization of Non-native Intermediate States. Journal of Proteins and Proteomics, 1 (2). pp. 43-51. ISSN 0975-8151

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Abstract

Cysteine proteases are vital to cell physiology and many plants secrete these proteases for defense purposes. Many recent studies have reported unusually high stabilities for several plant cysteine proteases which possibly enable these proteases to function under adverse environmental conditions. Here, we have examined the conformational features of a new plant cysteine protease heynein using spectroscopic tools to understand the basis for its robust functional stability. The studies revealed structural integrity over a wide range of pH (2.5-12.0), temperature (65 oC) and urea (8M). However, at pH 2.0, the protein gets acid-unfolded (UA-state) with exposed hydrophobic patches, which upon addition of more protons (pH 0.5) or anions (0.5 M KCl and 0.2 M Na2SO4) yields conformationally distinct refolded intermediates respectively termed: A-, I1- and I2-states. Strikingly, a high methanol level drives the UA-state into a predominantly beta -sheet rich conformation (O-state). We observed three-state unfolding kinetics of the I2-state by urea, possibly suggesting presence of two domains in the heynein molecule.

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