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Amino acids Thr56 and Thr58 are not essential for elongation factor 2 function in yeast
Stockholm University, Faculty of Science, The Wenner-Gren Institute .
Stockholm University, Faculty of Science, The Wenner-Gren Institute .
2007 (English)In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 274, no 20, 5285-5297 p.Article in journal (Refereed) Published
Abstract [en]

Yeast elongation factor 2 is an essential protein that contains two highly conserved threonine residues, T56 and T58, that could potentially be phosphorylated by the Rck2 kinase in response to environmental stress. The importance of residues T56 and T58 for elongation factor 2 function in yeast was studied using site directed mutagenesis and functional complementation. Mutations T56D, T56G, T56K, T56N and T56V resulted in nonfunctional elongation factor 2 whereas mutated factor carrying point mutations T56M, T56C, T56S, T58S and T58V was functional. Expression of mutants T56C, T56S and T58S was associated with reduced growth rate. The double mutants T56M/T58W and T56M/T58V were also functional but the latter mutant caused increased cell death and considerably reduced growth rate. The results suggest that the physiological role of T56 and T58 as phosphorylation targets is of little importance in yeast under standard growth conditions. Yeast cells expressing mutants T56C and T56S were less able to cope with environmental stress induced by increased growth temperatures. Similarly, cells expressing mutants T56M and T56M/T58W were less capable of adapting to increased osmolarity whereas cells expressing mutant T58V behaved normally. All mutants tested were retained their ability to bind to ribosomes in vivo. However, mutants T56D, T56G and T56K were under-represented on the ribosome, suggesting that these nonfunctional forms of elongation factor 2 were less capable of competing with wild-type elongation factor 2 in ribosome binding. The presence of nonfunctional but ribosome binding forms of elongation factor 2 did not affect the growth rate of yeast cells also expressing wild-type elongation factor 2.

Place, publisher, year, edition, pages
2007. Vol. 274, no 20, 5285-5297 p.
Keyword [en]
elongation factor 2, functional complementation, osmostress, phosphorylation, yeast
National Category
Cell Biology
Research subject
Cellbiology
Identifiers
URN: urn:nbn:se:su:diva-25111DOI: 10.1111/j.1742-4658.2007.06054.xISI: 000249882400009OAI: oai:DiVA.org:su-25111DiVA: diva2:198928
Available from: 2008-05-13 Created: 2008-05-12 Last updated: 2011-10-24Bibliographically approved
In thesis
1. Elongation factor 2: A key component of the translation machinery in eukaryotes: Properties of yeast elongation factor 2 studied in vivo
Open this publication in new window or tab >>Elongation factor 2: A key component of the translation machinery in eukaryotes: Properties of yeast elongation factor 2 studied in vivo
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Synthesis of proteins is performed by the ribosome, a large ribonucleoprotein complex. Apart from the ribosome, numerous protein factors participate in this process. Elongation factor 2 (eEF2) is one of these factors. eEF2 is an essential protein with a mol. mass of about 100 kDa. The amino acid sequence of eEF2 is highly conserved in different organisms. eEF2 from S. cerevisiae contains 842 amino acids. The role of eEF2 in protein synthesis is to participate in the translocation of tRNAs from the A- and P-sites on the ribosome to the P- and E-sites. This movement of tRNAs is accompanied by a simultaneous movement of mRNA by one codon. eEF2 consists of six domains referred to as domains G, G′ and II-V, belongs to the G-protein super-family and possesses all structural motifs characterizing proteins in this family. eEF2 binds to the ribosome in complex with GTP. After GTP hydrolysis and translocation, it leaves the ribosome bound to GDP. The rate of protein synthesis in the cell can be regulated by phosphorylation of eEF2. Phosphorylation occurs on two threonine residues, situated in the G domain of the factor. Phosphorylation of eEF2 is catalysed by Rck2-kinase in yeast which is activated in response to osmotic stress. Despite the high degree of conservation of the threonine residues, they are not essential for yeast cell under normal growth conditions. However, under mild osmotic stress the growth rate of the cells lacking threonine residues was decreased. Region where threonine residues are located, called Switch I. Cryo-EM reconstruction shows that this region adopts ordered conformation when the eEF2•GTP complex is bound to the ribosome but became structurally disordered upon GTP hydrolysis. Mutagenesis of individual amino acids in Switch I resulted in both functional and non-functional eEF2 depending on the site of mutation and the substituting amino acid. Both functional and non-functional Switch I mutants were able to bind to the ribosome, indicating that mutations did not abolish the capacity of the factor to bind GTP. Yeast eEF2 with Switch I region from E. coli was able to substitute the wild type protein in vivo, though the growth rate of these cells was severely impaired. The eEF2-dependent GTP hydrolysis can be activated by ribosome from heterologous sources as seen in vitro. However, eEF2 from A. thaliana, D. melanogaster and S. solfataricus could not substi-tute yeast eEF2 in vivo. This may indicate additional roles of eEF2 in the yeast cell, apart from translocation itself.

Place, publisher, year, edition, pages
Stockholm: Wenner-Grens institut för experimentell biologi, 2008. 56 p.
Keyword
Elongation factor 2, yeast, ribosome, phosphorylation, Switch I, site-directed mutagenesis, functional complementation
National Category
Cell Biology
Research subject
Cellbiology
Identifiers
urn:nbn:se:su:diva-7733 (URN)978-91-7155-634-9 (ISBN)
Public defence
2008-06-04, MA331, Söderstörns högskola, Alfred Nobels allé 7, Huddinge, 13:00
Opponent
Supervisors
Available from: 2008-05-13 Created: 2008-05-12Bibliographically approved
2. Ribosomal proteins L5, L15 and elongation factor 2, three vital components of the translation machinery: Functional features of RPL5, RPL15 and EF2 from Saccharomyces cerevisiae studied in vivo
Open this publication in new window or tab >>Ribosomal proteins L5, L15 and elongation factor 2, three vital components of the translation machinery: Functional features of RPL5, RPL15 and EF2 from Saccharomyces cerevisiae studied in vivo
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Protein synthesis is an essential, energy consuming and tightly regulated process in all living cells. A central core of the cellular protein-factory is a macromolecule called ribosome. Ribosomes are composed of ribosomal RNAs (rRNAs) and proteins (RPs). Additional components such as elongation factors (EFs) also contribute to this process. rRNAs are known as the catalytic constituents of the ribosome, while RPs are regarded as scaffold of the rRNA backbone. Despite this common view, in recent years, the functional importance of RPs has become more evident. In addition, RPs also carry extra-ribosomal functions some of which are linked to various diseases.

In the current thesis I have attempted to highlight the importance of the structural features of two ribosomal proteins, YrpL5 and YrpL15A, present in the large ribosomal subunit and YeEF2. The results presented here are based on mutagenesis analysis, combined with functional complementation approach in the baker’s yeast S.cerevisiae.

Introduced mutations show various degrees of cellular effects; YrpL15A tolerated inserted mutations greater than YrpL5. Nevertheless, YrpL15A proved to be more sensitive in its terminal-ends. This is presumably due to close contacts to the neighbouring molecules through these regions. On the other hand the N-terminal of YrpL5 displays a more permissive character for introduced mutations. In addition, A.thaliana orthologue to rpL15 could functionally substitute for yeast rpL15A. In contrast orthologues of rpL5 from A.thaliana, D.melanogaster and M. musculus were unable to functionally substitute for yeast rpL5. This could be an indication of species-specific features in YrpL5. Furthermore, two regulatory and highly conserved amino acids Thr56 and Thr58 displayed unessential functional role in yeast eEF2 under standard growth conditions. However, they showed to be important for YeEF2 function under mild osmotic stress. This may point to alternative regulatory mechanism for YeEF2.

Place, publisher, year, edition, pages
Stockholm: The Wenner-Gren Institute, Stockholm University, 2011. 58 p.
Keyword
Ribosome, Ribosomal protein, Elongation factor, Translation
National Category
Cell Biology
Research subject
Cell Biology
Identifiers
urn:nbn:se:su:diva-63520 (URN)978-91-7447-378-0 (ISBN)
Public defence
2011-11-25, lecture room E306, Arrheniuslaboratorierna, Svante Arrhenius väg 20 C, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2011-11-02 Created: 2011-10-21 Last updated: 2011-10-26Bibliographically approved

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