Electronic Theses and Dissertations

Identifier

528

Date

2012

Document Type

Dissertation (Access Restricted)

Degree Name

Doctor of Philosophy

Major

Biology

Committee Chair

Carlos Enrique Estrano

Committee Member

Judith Cole

Committee Member

Tit-Yee Wong

Committee Member

Andrew Liu

Abstract

Mitochondria and plastids were both acquired through different endosymbiotic events. Protein import into these two organelles has been well studied in some organisms. However, this process is not fully understood in organisms such as Giardia and Plasmodium both of which possess endosymbiotic organelles. Giardia lamblia acquired a mitochondria-like organelle known as the mitosome through endosymbiosis. Despite a fully sequenced genome, Tom 40 is the only component of the external membrane import apparatus that has been identified in G. lamblia. Using an overexpression system, we determined the functional conservation of the mitosomal protein import machinery by expressing higher eukaryotic mitochondrial proteins in Giardia mitosomes. Our results showed differential recognition of higher eukaryotic mitochondrial proteins, where NipSnap1 protein with an N-terminal targeting sequence was recognized by the mitosomal protein import machinery, while, Tom20 and Tom 22 both with internal targeting sequences were not recognized. This suggests divergence of the mitosomal protein import machinery from typical higher eukaryotic mitochondria. The parasite Plasmodium falciparum also acquired a plastid, known as the apicoplast through secondary endosymbiosis. The apicoplast has been identified as a potential drug target; however, protein import into this four membrane organelle is not fully understood. Attempts to isolate this organelle by three independent labs including ours were unsuccessful. For this reason we decided to pursue a different approach, using Euglena gracilis as a model. Similar to Plasmodium, Euglena acquired a plastid through secondary endosymbiosis and in Euglena biologically functional chloroplasts have been isolated. Since Euglena shares some common characteristics with dinoflagellates the Plasmodium ancestor, it is reasonable to conclude that there would be some conserved elements shared by the two organelles. We have successfully established the first protocol to separate envelope membranes from a multi-membrane plastid, an important step towards characterizing protein import in complex plastids.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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