From CellBiology

Individual Project - Spectrin

Various actin-binding proteins (ABP) are known to be found in the nucleus of cells and are responsible for the regulation actin filaments in the cytoplasm. Cellular processes such as chromatin remodeling, RNA processing, transcription and nuclear export greatly rely on nuclear actin. Actin-binding proteins thus play a significant role in the regulation of processes in the nucleus and the entire cell. An example of an actin binding protein is spectrin.

Spectrin is a cytoskeleton protein that is associated with the plasma membrane. It can be found in most vertebrate tissue and certain invertebrates. Spectrins provide the base structural meshwork for erythrocytes and researchers have therefore used erythrocytes as a standardized model to explore the properties of this protein.


• Two types of alpha subunits are present mammals, these are products of distinct genes

• Located on chromosome 9 in all mammalian tissues except mature erythrocytes

• Located on chromosome 1 in mature erythrocytes

• Birds and other animals are presumed to have single alpha subunits expressed in erythrocytes


The spectrin protein is a rod shaped, flexible molecule ranging from 200 to 260 nm in length. It is comprised of two non-identical subunits, α and β subunits, with molecular weights of 280 and 246 Kd respectively. Its side by side alignment forms the protein’s heterodimers, and a head to head alignment gives its tetramer structures. In many cases, there is a calmodulin binding site near the center of the alpha subunit of spectrins. (Note: this feature is absent in mammalian erythrocytes) Likewise, ankyrin binding sites are found in the middle of the beta subunits of the tetramers. Under high resolution electron microscopy, we will be able to see five to six rod shaped spectrin molecules linked to short actin filaments ranging from 30 to 50 nm in length. The linkage of these two develops a sheet of polygons and hexagons.

The primary structure of spectrin contains subunits of a 106-amino acid repeating motif. It is believed that each recurrent sequence invaginates into three α helixes, namely the spectrin repeat. [Image]


The main function of spectrin is its contribution to the cytoskeleton of cells. It gives cells support, locomotion and their overall shape.


Current Research

Previous research on spectrin has mostly been focused on the discovery of spectrin being the main constituent of erythrocyte membrane skeletons, as well as investigations of the major constituent proteins along with spectrin.



1. Bennett V and Lambert S (1991). The Spectrin Skeleton: From Red Cells to Brain. The Amercian Society for Clinical Investigation. 87:1483-1489

2. Djinovic-Carugo K, Gautel M, Ylanne J and Young P (2002). The spectrin repeat: a structural platform for cytoskeletal protein assemblies. Federation of European Biochemical Societies. Elsevier Science. 513: 119-123

3. Forget B.G, Winkelmann J.C (1993). Erythroid and nonerythroid spectrins. Blood. American Society of Hematology. 81:3171-3185

4. Fukalova J, Filimonenko V and Hozak P. Actin-binding protein in the nucleus. Institute of Molecular Genetics, Dept. of Biology of the Cell Nucleus, Academy of Sciences of the Czech Republic.

5. Ungewickell E and Gratzer W (1978). Self-Association of Human Spectrin, A Thermodynamic and Kinetic Study. Eur. J. Biochem. 88: 379-385

6. Viel A and Branton D (1996). Spectrin: on the path from structure to function. Current Opinion in Cell Biology. 8: 49-55


Lecture 4 - Nucleus

What did you find interesting and did not know about the nucleus?

From the nucleus lecture, I have learnt that the nucleus consists of two concentric membranes, which form the nuclear envelope. It was interesting to know that they break down during mitosis and also contain nuclear pores that make them permeable.

Lecture 5 - Exocytosis

What concept about exocytosis did you find difficult to understand?

Lecture 7 - Mitochondria

What types of cellular processes require lots of energy from the mitochondria?

The mitochondria produce energy (ATP) using energy that is stored in food by aerobic respiration. After glycolysis, pyruvate enters the mitochondrion to enter the Krebs cycle in order to complete the oxidation of organic fuel and finally produce ATP. Cellular processes such as signaling of cells, transportation of cells across cell membranes, cell differentiation, biosynthesis and locomotion require large amounts of the energy produced from the mitochondria.

Lecture 8 - Adhesion

What do the different "CAM" acronyms stand for?

CAM - cell adhesion molecules

Ng-CAM stands for Neuroglia Cell Adhesion Molecule

I-CAM stands for Intercellular Cellular Adhesion Molecule

L-CAM stands for Liver Cell Adhesion Molecule

Lecture 10

What is the name of the epidermal layer between the basal and granulosa layer and how does it relate to intermediate filaments?

The name of the epidermal layer between the basal and granulosa layer is called the stratum spinosum. Intermediate filaments are synthesized by cells of the stratum spinosum. These filaments help support the structure and also resists abrasion of the skin.

Lab 6 - Cytoskeleton Exercise

"If you've seen differences in the distribution of phenotypes in Tm4 over-expressing B35 cells versus control B35 cells, describe these differences. Formulate a hypothesis with regards to what changes on the molecular level may have occurred due to the over-expression of Tm4 that lead to morphological changes that you have observed"

Lecture 14 - Confocal Microscopy

What are the 2 main forms of generating confocal microscopy?

Lecture 15 - Cell Cycle

What does "S" stand for in the S phase?

The S phase stands for the synthesis phase. It occurs during interphase in between G1 phase and the G2 phase.