Colchicine-binding protein

Small molecules modulating microtubule assembly have played major roles as tools in microtubule research, in a manner closely related to their chemotherapeutic interest [1], Tubulin was first purified in the last century as the colchicine-binding protein proposed to be the subunit of cellular microtubules [2], More recently, a colchicine derivative was employed to help crystallization and determine the structure of tubulin by X-ray diffraction [3], The colchicine, vinblastine [4] and paclitaxel [5] sites are main drug binding sites of tubulin, to which many other substances bind. The discovery of microtubule stabilization by paclitaxel [6] prompted its clinical development [7] and a burst of research on new MSAs, as well as the generalized use of paclitaxel or docetaxel as convenient reagents to assemble (see Fig. 1), stabilize or detect microtubules in the laboratory. One example is the development... 

Weisenberg RC, Borisy GG, Taylor EW. The colchicine-binding protein of mammalian brain and its relation to microtubules. Biochemistry 1968 7 4466-4479. 

Tubulin, Colchicine-binding protein. The subunit protein of microtubules, which are large protein assemblies that play an important role in eukaryotic celt form determination aud dynamics. Microtubules have the genera]... 

Friedman PA etal. Biochim. Biophys Acta, 544 605, 1978. A colchicine-binding protein. 

Fig. 4 Diagram of the crystal structure of the T2R complex showing the binding sites of MT-destabilizing drugs (PDB entry 1Z2B) [13]. Protein subunits are represented as ribbons. RB3-SLD is colored orange, a-tubulin is purple, and p-tubulin is green. Small-molecule ligands are represented as spheres (vinblastine orange, colchicine red, GTP yellow, and GDP magenta). Colchicine binds to the p-subunit at the intradimer interface. Vinblastine binds at the interdimer interface...

The alkaloid colchicine binds tightly to tubulin and this characteristic has been used (Fig. 6.1) to isolate a tubulin-like fraction from H. diminuta, with properties similar to tubulin from other organisms. Furthermore, colchicine affects the qualitative distribution of [3H]proline-incorporated protein in this worm, with label accumulating in the parenchyma (195). This suggests that colchicine inhibits translocation in the tegument and provides evidence that microtubules within the internuncial processes facilitate movement of cell products from tegumentary cytons (Chapter 2) to the body surface for subsequent release. 

Mechanism of action Colchicine binds to tubulin, a microtubular protein, causing its depolymerization. This disrupts cellular functions, such as the mobility of granulocytes, thus decreasing their migration into the affected area. Furthermore, colchicine blocks cell division by binding to mitotic spindles. Colchicine also inhibits the synthesis and release of the leukotrienes (see Figure 39.14). 

Borisy GG, Taylor EW. The mechanism of action of colchicine. Binding of colchincine-3H to cellular protein. J. Cell. Biol. 

The effect of colchicine on inhibiting mitosis by disrupting microtubules has been known for many years, and now the detailed mode of action is becoming clear. The structural protein of tubules, tubulin, has alpha and beta subunits as well as subtypes of the beta form. Colchicine binds specifically to the beta subunit, and kinetics of the binding change... 

Microtubules are fibrous aggregates of the globular protein tubulin (Snyder and McIntosh, 1976 Olmsted and Borisy, 1973). They have an outer diameter of 25 nm, a wall 5 nm thick, and an inner hollow core 15 nm across. Microtubules may have a length from a fraction of a micrometer to several micrometers. Colchicine binds to tubulin and prevents its polymerization into microtubules. 

The cause of the cell cycle specificity of the bisindole alkaloids may be associated with the ability of these compounds to interact with the protein tubulin and thereby inhibit the polymerization (and depolymerization) of microtubules (16,17). In this respect the cellular pharmacology of vinca alkaloids is similar to that of other cytotoxic natural products such as colchicine or podophyllotoxin. On closer inspection, however, Wilson determined that the specific binding site on tubulin occupied by vinblastine or vincristine is chemically distinct from the site occupied by the other natural products (18). Subsequent experiments have determined that the maytansinoids, a class of ansa-macrocycles structurally distinct from the bisindoles, may bind to tubulin at an adjacent (or overlapping) site (19). A partial correlation of the antimitotic activity of these compounds with their tubulin binding properties has been made, but discrepancies in cellular uptake probably preclude any quantitative relationship of these effects (20). 

Human KB carcinoma cells resistant to vinblastine and other drugs have been shown to exhibit increased membrane vesicular binding of tritiated vinblastine, and this binding is correlated with photoaffinity labeling of a 150,000- to 170,000-dalton protein in the vesicles. Labeling of this protein is inhibited by vinblastine, vincristine, and verapamil but not by colchicine (79). The failure of colchicine to inhibit the labeling of the membrane protein is unexpected since the cells from which the protein was isolated are resistant to colchicine as well as vinblastine. 

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