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Crystal Structure of the Human CCA-adding Enzyme: Insights into Template-independent Polymerization

Authors :
Mario Mörl
Andreas S. Reichert
Clemens Steegborn
Robert Huber
Martin Augustin
Heike Betat
Source :
Journal of Molecular Biology. 328:985-994
Publication Year :
2003
Publisher :
Elsevier BV, 2003.

Abstract

All tRNA molecules carry the invariant sequence CCA at their 3'-terminus for amino acid attachment. The post-transcriptional addition of CCA is carried out by ATP(CTP):tRNA nucleotidyltransferase, also called CCase. This enzyme catalyses a unique template-independent but sequence-specific nucleotide polymerization reaction. In order to reveal the molecular mechanism of this activity, we solved the crystal structure of human CCase by single isomorphous replacement. The structure reveals a four domain architecture with a cluster of conserved residues forming a positively charged cleft between the first two domains. Structural homology of the N-terminal CCase domain to other nucleotidyltransferases could be exploited for modeling a tRNA-substrate complex. The model places the tRNA 3'-end into the N-terminal nucleotidyltransferase site, close to a patch of conserved residues that provide the binding sites for CTP and ATP. Based on our results, we introduce a corkscrew model for CCA addition that includes a fixed active site and a traveling tRNA-binding region formed by flexible parts of the protein.

Details

ISSN :
00222836
Volume :
328
Database :
OpenAIRE
Journal :
Journal of Molecular Biology
Accession number :
edsair.doi.dedup.....4afd85baed8a6d938398e1f49447a7ec