Septin structure and filament assembly
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REVIEW
Septin structure and filament assembly Napoleão Fonseca Valadares 1 & Humberto d’ Muniz Pereira 2 & Ana Paula Ulian Araujo 2 & Richard Charles Garratt 2
Received: 5 August 2017 / Accepted: 17 August 2017 # International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany 2017
Abstract Septins are able to polymerize into long apolar filaments and have long been considered to be a component of the cytoskeleton alongside intermediate filaments (which are also apolar in nature), microtubules and actin filaments (which are not). Their central guanosine triphosphate (GTP)-binding domain, which is essential for stabilizing the filament itself, is flanked by N- and C-terminal domains for which no direct structural information is yet available. In most cases, physiological filaments are built from a number of different septin monomers, and in the case of mammalian septins this is most commonly either three or four. Comprehending the structural basis for the spontaneous assembly of such filaments requires a deeper understanding of the interfaces between individual GTP-binding domains than is currently available. Nevertheless, in this review we will summarize the considerable progress which has been made over the course of the last 10 years. We will provide a brief description of each structure determined to date and comment on how it has added to the body of knowledge which is rapidly growing. Rather than simply repeat data which have already been described in the literature, as far as is possible we will try to take advantage of the full set of information now available (mostly derived from human septins) and draw the reader’s attention to some of the This article is part of a Special Issue on ‘Latin America’ edited by Pietro Ciancaglini and Rosangela Itri. * Richard Charles Garratt [email protected] 1
Departamento de Biologia Celular, Universidade de Brasília, Brasília 70910-900, Brazil
2
Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador Sancarlense, 400, São Carlos, SP 13560-590, Brazil
details of the structures themselves and the filaments they form which have not be commented on previously. An additional aim is to clarify some misconceptions. Keywords Septins . Filament assembly . GTP-binding domain . N- and C-terminal domains . Interfaces . Crystal structures
A brief summary Septins are cytoskeletal proteins capable of self-association, polymerization and binding to cell membranes (Kinoshita 2003; Bridges et al. 2014; Garcia et al. 2016). They were originally identified in yeast mutants deficient in the completion of the cell cycle (Hartwell 1971) and were subsequently localized to the septum during cell division, hence the name. They are present in a variety of eukaryotic cells, playing a fundamental role in cytokinesis as well as in the formation of diffusion barriers. The latter serve to restrict membrane components to a particular cellular component, for example the primary cilium, by limiting the rate of lateral diffusion (Hu et al. 2010). The
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