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Dual Role for $Zn^{2+}$ in Maintaining Structural Integrity and Inducing DNA Sequence Specificity in a Promiscuous Endonuclease

Saravanan, Matheshwaran and Vasu, Kommireddy and Ghosh, Soumitra and Nagaraja, Valakunja (2007) Dual Role for $Zn^{2+}$ in Maintaining Structural Integrity and Inducing DNA Sequence Specificity in a Promiscuous Endonuclease. In: Journal of Biological Chemistry, 282 (44). pp. 32320-32326.

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We describe two uncommon roles for $Zn^{2+}$ in enzyme KpnI restriction endonuclease (REase). Among all of the REases studied, KpnI REase is unique in itsDNAbinding and cleavage characteristics. The enzyme is a poor discriminator of DNA sequences, cleaving DNA in a promiscuous manner in the presence of $Mg^{2+}$. Unlike most Type II REases, the active site of the enzyme comprises an HNH motif, which can accommodate $Mg^{2+}$,$Mn^{2+}$, or $Ca^{2+}$. Among these metal ions,$Mg^{2+}$ and $Mn^{2+}$ induce promiscuous cleavage by the enzyme, whereas $Ca^{2+}$-bound enzyme exhibits site-specific cleavage. Examination of the sequence of the protein revealed the presence of a zinc finger CCCH motif rarely found in proteins of prokaryotic origin. The zinc binding motif tightly coordinates zinc to provide a rigid structural framework for the enzyme needed for its function. In addition to this structural scaffold, another atom of zinc binds to the active site to induce high fidelity cleavage and suppress the $Mg^{2+}$- and $Mn^{2+}$-mediated promiscuous behavior of the enzyme. This is the first demonstration of distinct structural and catalytic roles for zinc in an enzyme, suggesting the distinct origin of KpnI REase.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to The American Society for Biochemistry and Molecular Biology.
Department/Centre: Division of Biological Sciences > Microbiology & Cell Biology
Depositing User: sidhartha sahoo
Date Deposited: 17 Dec 2008 12:06
Last Modified: 19 Sep 2010 04:52
URI: http://eprints.iisc.ac.in/id/eprint/16525

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