Description:
<jats:title>Abstract</jats:title>
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<jats:title>Background</jats:title>
<jats:p>Phytocystatins are natural inhibitors of cysteine protease, and may regulate endo- or exo-genous proteolytic activities in plants. They are classified into Group I and II differing by the presence of C-terminal extension of Group II. A cDNA fragment encoding a Group II phytosystatin, SiCYS was previously obtained from sesame seeds.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>SiCYS as well as its two structural domains, N-terminal and C-terminal domains (SiCYS-N and SiCYS-C), was expressed in <jats:italic>Escherichia coli</jats:italic>. The recombinant SiCYS and SiCYS-N showed inhibitory activity against papain. The <jats:italic>K</jats:italic> i values of SiCYS and SiCYS-N were ~1.9 ×10<jats:sup>-8</jats:sup> M and ~7.9 ×10<jats:sup>-8</jats:sup> M, respectively. All the three recombinants possessed comparable ability to inhibit spore germination of <jats:italic>Trichoderma reesei</jats:italic>, <jats:italic>Aspergillus sydowii</jats:italic>, and <jats:italic>Helminthosporium sesamum</jats:italic>. Similar protein profile including proteases in germinating seeds was found in proteins purified by the SiCYS, SiCYS-N or SiCYS-C coupling affinity column.</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>SiCYS exhibited more effective papain-inhibitory activity than SiCYS-N; while SiCYS-C had almost no inhibitory activity. All displayed similar antifungal activities indicating that there is no correlation between antifungal and papain-inhibitory activities. Structural and sequence analyses suggest that the C-terminal domain of SiCYS may be originated from gene duplication to enhance its inhibitory activity.</jats:p>
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