Functional and Structural Characterization of Actin from Leishmania donovani

Abstract

“Actin is interesting”. We state this not just because actin is so plentiful that it is the single most abundant protein in many eukaryotic cells. We think that actin remains interesting because after more than 60 years of study, fundamental questions about actin structure and dynamics and how these determine function remain unanswered. Even in most of the articles related to actin structure and function, we generally encounter that “actin is an evolutionary conserved molecule” and this is just because it is so highly conserved that between humans and chickens, there have been no amino acid changes in the 375 residues present in the skeletal muscle isoform. We will not attempt to summarize and extend the known conventional actin in this study. Indeed, a search of PubMed for “actin” retrieves ~55,000 publications! Rather, we will focus on an unconventional, novel homolog of actin from Leishmania donovani (LdACT), few related issues involving the structure of the actin monomer and polymer and spend as much time discussing what we still do not know about actin as we spend reviewing what we do know. Moreover, we will try to summarize the basic functional and structural changes that occurred in actin during its molecular journey from prokaryotes to eukaryotes via an intermediate, trypanosomatid homolog of actin from a primitive eukaryotic organism, Leishmania donovani. We have divided the entire study in three chapters. We started Chapter 1 with a comparative detail of prokaryotic homologs of actin, and conventional eukaryotic actin and extended it to the novel functions of nuclear actin. Chapter 2 describes the functional and structural characterization of actin from Leishmania donovani, where we have compared the functional biochemical properties of LdACT with conventional rabbit muscle actin (RbACT) and focuses the structural changes in LdACT which could be responsible for its observed differential biochemical behaviour. Among flagellated descendants of these primitive eukaryotes, a high degree of complex organization also persist in kinetoplast DNA (kDNA) network, which is structurally the most complex mitochondrial DNA in nature. In Chapter 3, we describe the binding of LdACT with DNA, its association with kDNA network and explored the participation of LdACT in its dynamic polymerization state, in kDNA remodeling. Finally, bibliography in alphabetical order has been put at the end of thesis.