Cytoskeleton Proteins

Calcyclin (S100A6) is a member of the S100 family of proteins containing 2 EF-hand calcium-binding motifs. S100 proteins are localized in the cytoplasm and/or nucleus of a wide range of cells, involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. This protein may function in stimulation of Ca2+-dependent insulin release, stimulation of prolactin secretion and exocytosis. Chromosomal rearrangements and altered expression of this gene have been implicated in melanoma.

Tau protein promotes microtubule assembly and stability. Tau is also involved in the establishment and maintenance of neural polarity. The C-terminus domain of Tau binds to axonal microtubules whereas the N-terminus domain binds to neural plasma membrane components, therefore suggesting that Tau protein functions as a linker between the two. Axonal polarity is predetermined by tau localization in the domain of the cell body defined by the centrosome. The short isoforms allow plasticity of the cytoskeleton whereas the longer isoforms may preferentially play a role in its stabilization.

GAP-43 (Growth associated protein-43, neuromodulin) is a cytoplasmic axonal membrane protein that is involved in the neuronal outgrowth and synaptic plasticity of developing and regenerating neurons . Palmitoylated GAP-43 attaches to the membrane via lipid rafts, while the unmodified form is a component of the centrosome. GAP-43 binds to calmodulin in the absence of Ca++ and functions as a substrate for PKC in the nerve growth factor (NGF) signaling pathway.

Ankyrin-1 attaches (ANK1) integral membrane proteins to cytoskeletal elements. Erythrocyte ankyrins link spectrin (beta chain) to the cytoplasmic domain of the erythrocytes anion exchange protein. Defects in ANK1 are a cause of spherocytosis type 1 (SPH1), also called hereditary spherocytosis type 1 (HS1). Spherocytosis is a hematologic disorder leading to chronic hemolytic anemia and characterized by numerous abnormally shaped erythrocytes which are generally spheroidal. Inheritance can be autosomal dominant or recessive.