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Functional features of the C-terminal region of yeast ribosomal protein L5
Södertörn University, School of Life Sciences. Stockholm University.
Södertörn University, School of Life Sciences. Stockholm University.
Södertörn University, School of Life Sciences. Stockholm University.
Södertörn University, School of Life Sciences.
2008 (English)In: Molecular Genetics and Genomics, ISSN 1617-4615, E-ISSN 1617-4623, Vol. 280, no 4, 337-350 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to analyze the functional importance of the C-terminus of the essential yeast ribosomal protein L5 (YrpL5). Previous studies have indicated that the C-terminal region of YrpL5 forms an alpha-helix with a positively charged surface that is involved in protein-5S rRNA interaction. Formation of an YrpL5 center dot 5S rRNA complex is a prerequisite for nuclear import of YrpL5. Here we have tested the importance of the alpha-helix and the positively charged surface for YrpL5 function in Saccharomyces cerevisiae using site directed mutagenesis in combination with functional complementation. Alterations in the sequence forming the putative alpha-helix affected the functional capacity of YrpL5. However, the effect did not correlate with a decreased ability of the protein to bind to 5S rRNA as all rpL5 mutants tested were imported to the nucleus whether or not the alpha-helix or the positively charged surface were intact. The alterations introduced in the C-terminal sequence affected the growth rate of cells expressing mutant but functional forms of YrpL5. The reduced growth rate was correlated with a reduced ribosomal content per cell indicating that the alterations introduced in the C-terminus interfered with ribosome assembly.

Place, publisher, year, edition, pages
2008. Vol. 280, no 4, 337-350 p.
National Category
Biochemistry and Molecular Biology Genetics
Identifiers
URN: urn:nbn:se:sh:diva-14121DOI: 10.1007/s00438-008-0369-7ISI: 000258902300007PubMedID: 18751732Scopus ID: 2-s2.0-51349101530OAI: oai:DiVA.org:sh-14121DiVA: diva2:467049
Available from: 2011-12-18 Created: 2011-12-16 Last updated: 2017-02-13Bibliographically approved
In thesis
1. Ribosomal proteins L5 and L15: Functional characterisation of important features, in vivo
Open this publication in new window or tab >>Ribosomal proteins L5 and L15: Functional characterisation of important features, in vivo
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Protein synthesis is a highly regulated and energy consuming process, during which a large ribonucleoprotein particle called the ribosome, synthesizes new proteins. The eukaryotic ribosome consists of two unequal subunits called: small and large subunits. Both subunits are composed of ribosomal RNA (rRNA) and ribosomal proteins (r-proteins).

Although rRNAs build the matrix of the ribosome and carries out catalysing of the peptide-bond formation between amino acids, r-proteins also appear to play important structural and functional roles. The primary role of r-proteins is to initiate the correct tertiary fold of rRNA and to organize the overall structure of the ribosome.

In this thesis, I focus on two proteins from the large subunit of the eukaryotic ribosome: r-proteins L5 and L15 from bakers yeast S. cerevisiae. Both r-proteins are essential for ribosome function. Their life cycle is primarily associated with rRNA interactions. As a consequence, the proteins show high sequence homology across the species borders. Furthermore, both L5 and L15 are connected to human diseases, which makes the study their role in ribosome biogenesis and ribosome function important.

By applying random- and site-directed mutagenesis, coupled with functional complementation tests, I aimed to elucidate functionally regions in both proteins, implicated in transport to the cell nucleus, protein-protein interactions and/or rRNA binding. The importance of individual and multiple amino acid exchanges in the primary sequence of rpL5 and rpL15 were studied in vivo. The obtained results show that S. cerevisiae rpL15 was tolerant to amino acid exchanges in the primary sequence, whereas rpL5 was not. Consequently, A. thaliana rpL15 could substitute for the function of wild type rpL15, whereas none of the tested orthologous proteins to rpL5 could substitute yeast rpL5 in vivo. These observations further emphasize the importance of studying r-proteins as separate entities in the ribosome context.

Place, publisher, year, edition, pages
Stockholm: Stockholm University, 2009. 50 p.
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:sh:diva-30701 (URN)978-91-7155-896-1 (ISBN)
Public defence
2009-06-16, MB 503, Södertörns högskola, Alfred Nobels allé 7, 10:00 (English)
Opponent
Supervisors
Available from: 2016-08-05 Created: 2016-08-05 Last updated: 2016-08-05Bibliographically approved
2. 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-Gren Institute for Experimental Biology, Stockholm university, 2008. 56 p.
Keyword
Elongation factor 2, yeast, ribosome, phosphorylation, Switch I, site-directed mutagenesis, functional complementation
National Category
Cell Biology
Identifiers
urn:nbn:se:sh:diva-32038 (URN)978-91-7155-634-9 (ISBN)
Public defence
2008-06-04, MA331, Alfred Nobels allé 7, Huddinge, 13:00 (English)
Opponent
Supervisors
Available from: 2017-02-13 Created: 2017-02-13 Last updated: 2017-02-13Bibliographically approved

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