Study on Actin Cytoskeleton Complexity with a Phylogenetic Analysis of ARP 2/3 Complexes and Formins

Sabu, Chinchumol K. (2015) Study on Actin Cytoskeleton Complexity with a Phylogenetic Analysis of ARP 2/3 Complexes and Formins. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Chinchumol K Sabu (10MS81)) MS_Thesis-Chinchu(10MS81).pdf - Submitted Version Restricted to Repository staff only Download (967kB)

Abstract

Actin is a multifunctional protein that forms the microfilament system in all eukaryotic cells and crucial for basic functions ranging from cell signaling, vesicle and organelle movement, cell division and cytokinesis. Actin is a very ancient molecule and is generally assumed to find its origin at the onset of eukaryotic life (1.5–2 billion years ago). Actin cytoskeleton in vivo is not entirely composed of actin only, a group of proteins called Actin Binding Proteins (ABPs) helps in the maintenance and function of actin inside the cell. Interaction between several ABPs assists in the assembly and disassembly of actin filaments and arranging themselves to form functional higher order networks. These ABPs are structurally and functionally different from each other. So far, more than 150 ABPs are estimated in humans and around 50 in yeast. Presence of ABPs in almost all branches of the eukaryotic kingdom indicates that, it must be originated early in evolution and has a vital functional importance in organisms. Among Actin binding proteins, ARP (Actin Related Protein) 2/3complex and Formin are two well-studied potent actin nucleators. After revising the distribution of actin binding proteins along the major eukaryotic groups revealed the pattern of distribution with un-ending complexity. Examples: the motile Dictyostelium Discoideum has ten formins but non-motile Budding Yeast has only two formins present in them. Lower Protozoan’s like Leishmania major has merely two formins present in them, whereas, reasonably large number of formin has been detected in Naegleria gruberi (Excavata) which is famed for its ability to change from amoeba to flagellate and also for its elaborate microtubule cytoskeleton. But ARP 2/3 complex, which has the same nucleator function shows very less diversity compared to formin. Phylogenetic trees which give a visual interpretation of evolutionary interactions, based on DNA or the protein sequences among diverse taxonomic groups, are an excellent tool to understand such complex evolutionary processes. It is believed that nature possesses a native endeavor to become more complex with ongoing evolutionary needs of organisms. Here, we are trying to understand the complexity of the evolution of the actin cytoskeleton with the phylogenetic analysis of ARP 2/3 complex and formin. This can give greater insight regarding the evolution of actin cytoskeleton and its functional importance

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