"Zn-Link": A Metal-Sharing Interface that Organizes the Quaternary Structure and Catalytic Site of the Endoribonuclease, RNase E
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- 作者：Anastasia J. Callaghan ; Yulia Redko ; Loretta M. Murphy ; J. Gü ; nter Grossmann ; David Yates ; Elspeth Garman ; Leopold L. Ilag ; Carol V. Robinson ; Martyn. F. Symmons ; Kenneth J. McDowall ; and Ben F. L
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：March 29, 2005
- 年：2005
- 卷：44
- 期：12
- 页码：4667 - 4675
- 全文大小：197K
- 年卷期：v.44,no.12(March 29, 2005)
- ISSN：1520-4995
文摘
Ribonuclease E is an essential hydrolytic endonuclease in Escherichia coli, and it plays acentral role in maintaining the balance and composition of the messenger RNA population. The enzymeis also required for rRNA and tRNA processing. We have shown earlier that the highly conserved catalyticdomain of E. coli RNase E is a homotetramer [Callaghan, A. J. et al. (2003) Biochemistry 42, 13848-13855]. Here, we report that this quaternary organization requires zinc. Two protomers share a singlezinc ion, and quantitative analysis indicates that each protein contributes two cysteine thiols toward thecoordination of the metal. The candidate cysteines are part of a motif that is conserved in the RNase Eprotein family, and mutation of these residues causes the partial loss of zinc, the complete disruption ofthe tetramer into dimers, and effective catalytic inactivation. However, these mutations do not affect RNAbinding. The tetramer can be artificially maintained by disulfide bond formation, which fully displacesthe zinc but largely preserves the catalytic activity. Thus, catalytic activity does not require zinc directlybut does require the quaternary structure, for which the metal is essential. We propose that the RNase Etetramer has two nonequivalent subunit interfaces, one of which is mediated by a single, tetrathiol-zinccomplex, which we refer to as a "Zn-link" motif. One or both interfaces organize the active site, whichis distinct from the primary site of RNA binding.