A protein involved in cytokinesis and also functions in maintaining cell morphology
Septins belong to a group of GTP-binding proteins in eukaryotic cells (except in plant cells1). They form a protein complex by assembling and interacting with each other. Typically, they form nonpolar filaments, filament bundles, rings, or cages. When they form complexes they become essential in maintaining cell morphology. They provide attachment points for other proteins inside the cell. In yeast cells, they provide structural support at the septum when the yeast cells divide. This is from where their name was derived.2
Septins have weight ranging from 30-65 kDa. A septin is comprised of proline rich N-terminus with a phosphoinositide binding motif (for membrane association), a GTP-binding domain, a Septin Unique Element domain, and a C-terminal extension with a coiled coil domain. 3
Septins that form filaments are considered as one form of cytoskeleton in eukaryotic cells. A cytoskeleton is a cytoplasmic structure composed of protein filaments and microtubules in the cytoplasm, and has a role in controlling cell shape, maintaining intracellular organization, and in cell movement. The other types of cytoskeletons are microfilaments, microtubules, intermediate filaments, and spectrin.
Septins that assemble and form a scaffolding protein complex, which is involved in providing structural support especially during cell division. They act as attachment points for other proteins inside the cell. They may serve as a barrier in between intracellular compartments; they prevent diffusion of molecules from one site to another inside the cell. In yeast cell, septins are involved in mitosis and sporulation. In particular, Cdc3, Cdc10, Cdc11, Cdc12, Shs1 are mitotic septins that aid in cell division by forming a ring structure at the septum. They position the mitotic spindle, cytokinesis, cell polarity, and chitin deposition. As for the sporulating septins, they are Spr3 and Spr28. They are involved in spore formation. In human cells, recent study revealed that septins apparently were involved in immune defense as they build a wall barrier around pathogenic bacteria in order to prevent the latter from invading other cells. 4 Septins in humans are also involved in cytokinesis, neurogenesis, and cilium formation. In humans, 13 genes are involved in the genetic coding for septins. The septins are grouped into four subfamilies: (1) SEPT2 (SEPT1, SEPT4, SEPT5), (2) SEPT3 (SEPT9, SEPT12), (3) SEPT6 (SEPT8, SEPT10, SEPT11, SEPT14), and (4) SEPT7. Genetic mutation involving such genes may lead to neurodegenaritve conditions (e.g. Alzheimer’s disease), leukemia, and colon cancer.
- septum + –in
- Neubauer, K. & Zieger, B. (2017). “The Mammalian Septin Interactome”. Frontiers in Cell and Developmental Biology. 5: 3.
- Douglas, L. M., Alvarez, F. J., McCreary, C., & Konopka, J. B. (2005). “Septin function in yeast model systems and pathogenic fungi”. Eukaryotic Cell. 4 (9): 1503–12.
- Mostowy, S. & Cossart, P. (2012). “Septins: the fourth component of the cytoskeleton”. Nat. Rev. Mol. Cell Biol. 13 (3): 183–94.
- Mascarelli, A. (December 2011). “Septin proteins take bacterial prisoners: A cellular defence against microbial pathogens holds therapeutic potential”. Nature.
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