Molecular Biology and Genetics MS Thesis Defense by Güleycan Lutfullahoğlu Bal

KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

MOLECULAR BIOLOGY AND GENETICS

MS THESIS DEFENSE BY GÜLEYCAN LUTFULLAHOĞLU BAL

Title: Bacterial tail anchors can target to the mitochondrial outer membrane and to peroxisomes

Speaker: Güleycan Lutfullahoğlu Bal

Time: December 28, 2017, 14:00

Place: ENG B15

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Assist. Prof. Ayşe Koca Çaydaşı (Advisor, Koç University)

Assist. Prof. Cory. D. Dunn (co-Advisor, Koç University)

Prof. I. Halil Kavaklı, (Koç University)

Assist. Prof. Yongsoo Park (Koç University)

Prof. Zeynep Petek Çakar (Istanbul Technical University)

Abstract:

Mitochondria are mostly double membrane bound organelles, surrounded by inner and outer membranes. Mitochondria are unique, having their own genetic material and a complete translation system. Yet, most of the mitochondrial proteins are produced in the cytosol, as a consequence of the evolutionary origin of mitochondria. Accordingly, an α-proteobacterial endosymbiont within the eukaryotic cell was transformed into the mitochondrion and reduced its genomic size by transferring most of its genes to the host nucleus. Translocation of such nuclear encoded proteins to the mitochondria requires special translocases found both at the inner and the outer membrane. As the conserved mitochondrial translocase of the outer membrane (TOM) complex seems to require pre-existing TOM complexes for membrane insertion, evolution of the initial translocon for re-targeting those proteins back to mitochondria is still a matter of debate. In order to find the possible bacterial origins of mitochondrial translocation machinery, based on a previous a survey in Escherichia coli proteome, we studied self-inserting, tail-anchored bacterial polypeptides that might have formed the initial gate allowing proteins to access mitochondria from the cytosol. Indeed, predicted tail anchor (TA) sequences of bacterial DUF883 family proteins, including ElaB and YqjD TAs, were targeted and inserted at the mitochondrial outer membrane within the budding yeast Saccharomyces cerevisiae. In addition, we also found that the YgiM TA localized to yeast peroxisomes. Our results support the view that eukaryotic cells are able to process membrane targeting signals of bacterial proteins acquired via lateral gene transfer, enabling us to suggest a scenario in which mitochondrial protein translocation was initially allowed by tail-anchored proteins.