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Role of residue 248 in Escherichia coli RNase P RNA mediated cleavage
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology. (Leif A. Kirsebom)ORCID iD: 0000-0001-5841-0991
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Abstract tRNA genes are transcribed as precursors and ribonuclease P (RNase P) generates the 5' end of tRNAs in the cell. It has been suggested that residue -1 (the residue immediately 5' of the scissile bond) in the substrate interacts with the well-conserved RNase P RNA (RPR) residue A248 (Escherichia coli numbering). The way A248 interacts with residue -1 is not clear. To gain insight into the role of A248, we analyzed cleavage as a function of A248 substitutions and N-1 nucleobase identity by using pre-tRNA and three all-ribo model substrates. Our findings are consistent with a model where the structural topology of the active site varies and depends on the identity of the nucleobases at, and in proximity to, the cleavage site and their potential to interact. This leads to positioning of Mg2+ that activates the water that acts as the nucleophile resulting in efficient and correct cleavage. Furthermore, we propose that the role of A248 is to exclude bulk water from access to the amino acid acceptor stem, thereby preventing non-specific hydrolysis of the pre-tRNA. Finally, base stacking is discussed as a way to protect functionally important base-pairing interactions from non-specific hydrolysis, thereby ensuring high fidelity during RNA processing and the decoding of mRNA.

Keywords [en]
RNase P/Ribozyme/Divalent metal ions/tRNA precursors/ tRNA processing.
National Category
Biochemistry and Molecular Biology
Research subject
Biology with specialization in Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-339605OAI: oai:DiVA.org:uu-339605DiVA, id: diva2:1176238
Available from: 2018-01-21 Created: 2018-01-21 Last updated: 2018-01-22
In thesis
1. Investigation of RNase P active site residues and catalytic domain interaction
Open this publication in new window or tab >>Investigation of RNase P active site residues and catalytic domain interaction
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

RNase P is an essential endoribonuclease responsible for the maturation of the tRNA 5’end. The RNase P family encompasses the ribozyme based, RNase P RNP, and proteinaceous RNase P (PRORP). The ribozyme based RNase P is widely distributed in most species while PRORP has so far mainly been found in some eukaryotic cells.

The RNase P RNP contains one RNA subunit (RPR), which is the catalytic moiety, and one or more protein subunits. The structural topology of the RPR is crucial for RNase P RNP to correctly and efficiently maintain its function. The RPR is composed of domains such as the specificity (S) and catalytic (C) domains, and structural elements that connect these.

The objectives of my thesis were to study the importance of structural elements in the C-domain of the RPR with respect to substrate interaction and catalysis. Another objective was to study substrate interaction in PRORP-mediated catalysis, and to compare RNase P RNP- and PRORP-mediated cleavage. To achieve this I have studied cleavage of both pre-tRNA and model hairpin loop substrates with RPR variants carrying deletions and base substitutions, and PRORP1 from Arabidopsis thaliana.

My data provide evidence for an intra domain interaction, referred to as the P6-mimic, in the RPR C-domain. The P6-mimic forms when the S-domain of the RPR is deleted and it contributes to catalysis. The inter domain P8/P18 interaction, which connects the S- and the C-domains, plays an important role for catalysis. My data suggest that, in the absence of the S-domain, P18 does not contribute to catalysis raising the possibility that the P8/ P18-interaction acts as a structural mediator between the TSL/ TBS-interaction site in the S-domain and the active center that ensures correct and efficient cleavage. This is consistent with that RNase P RNP operates through an induced fit mechanism.  

Furthermore, on the basis of biochemical and genetic data the well-conserved A248 in the RPR has been proposed to form a cis Watson-Crick/Watson-Crick (cis WC/WC) pair with the residue immediately 5' of the cleavage site, N-1, in the substrate. My data does not support this cis WC/WC pairing. Rather, the data are consistent with a model where the structural topology of the active site varies and depends on the identity of the nucleobases at, and in proximity to, the cleavage site and their potential to interact. As a consequence, this affects the positioning of Mg2+ that activates the water that acts as the nucleophile resulting in efficient and correct cleavage. In this scenario it is suggested that the role of A248 is to exclude bulk water from accessing the amino acid acceptor stem and thereby prevent non-specific hydrolysis of the pre-tRNA. In a broader perspective, base stacking might be a way to prevent access of water to functionally important base pairing interactions, and thereby ensuring high fidelity during RNA processing and decoding of mRNA.

As for RNase P RNP, my studies on PRORP1 indicate the importance of the identity of N-1 and the N-1: N+73 base pair in the substrate for efficient and correct cleavage. Although, the data indicate similarities they also provide key differences in substrate recognition by RNase P RNP and PRORP1 where the RNP form appears to require more recognition determinants for cleavage site selection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1623
Keywords
RNase P, Ribozyme, PRORP, Induced fit model, RNase P-pre-tRNA interaction
National Category
Biochemistry and Molecular Biology
Research subject
Biology with specialization in Molecular Biology
Identifiers
urn:nbn:se:uu:diva-339607 (URN)978-91-513-0214-0 (ISBN)
Public defence
2018-02-22, B/C4:305, Biomedical Center, Husargatan 3, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2018-01-31 Created: 2018-01-21 Last updated: 2018-05-21

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