Fig 2: Structure of microtubules

Recently, I issued a post about a method which allows measuring microtuble binding capabilities of proteins of interest. Today, I invite you to look at methods for measuring the dynamic polymerisation of tubulin to microtubules and to detect the impact of compounds or other variables in your experiments on this process.

Fig 1: Electron micrograph of microtubules (100,000x)

Tubulin represents one of the major cytoskeleton structures. It plays an important role in cell structure, intracellular transport, and mitosis. In eukaryotic cells, tubulin polymerizes to form structures called microtubules (MTs) (Fig. 1). When tubulin polymerizes it initially forms proto-filaments, MTs consist of 13 protofilaments and are 25nm in diameter, each um of MT length is composed of 1650 heterodimers. Microtubules are highly ordered fibers that have an intrinsic polarity, shown schematically in Figure 2. Tubulin can polymerize from both ends in vitro, however, the rate of polymerization is not equal. It has therefore become the convention to call the rapidly polymerizing end the plus-end of a microtubule and the slowly polymerizing end the minus-end. In vivo, the plus end of a microtubule is distal to the microtubule organizing center.

You suspect your protein binds to microtubules? That it might stabilize or destabilize these filamentous structures? Then this post is here to help you to find a meaningful assay to validate your assumption.

For one year now,  SiR-Actin and SiR-Tubulin, the second generation of tools to stain actin and tubulin in living cells, have been available on the market – and although it may sound like an overstatement, these stains have changed the world of Live Cell Imaging.

Colchicine chemical structure (64-86-8).

Microtubules are key components of the cytoskeletal structure of eukaryotic cells. Composed of alpha- and beta- tubulin sub-units, microtubules are dynamic entities with pivotal cellular roles (e.g. division and mitosis). Because of these unique characteristics, the first microtubule-based anti-cancer drugs have been described in the early 70’s. Here, we will review the 6 most popular small compounds active on tubulin polymerization and microtubules which are regularly used in today’s microtubule-centred in vitro assays.

Microtubule depolymerizing/inhibitor agents

1. Ansamitocin P3 (CAS# 66547-09-9) is a fungal metabolite from Actinosynnema pretiosum. Ansamitocin P3 is a maytansine analog which displays potent cytotoxicity against various human tumor cell lines. Maytansine (and analogs) cause extensive disassembly of microtubules by interacting with tubulin molecules.
2. Colchicine (CAS# 64-86-8) is a naturally occurring alkaloid acting as an antimitotic agent. It binds to tubulin and depolymerizes microtubules. Colchine has been shown to induce apoptosis in a variety of cell lines.
3. Nocodazole (CAS# 31430-18-9) is an anti-mitotic agent (cell cycle arrest at G2/M phase) disrupting microtubules by binding to ß-tubulin and thereby inhibiting microtubule dynamics. It causes a disruption of mitotic spindle function and fragmentation of the Golgi complex. Nocodazole also activates the JNK/SAPK signaling pathway and induces apoptosis in a variety of cell lines.
4. Vinblastine sulfate (CAS# 143-67-9) is a semi-synthetic alkaloidal anticancer agent. It induces cell cycle arrest at G2/M phase by inhibiting mitotic spindle formation. Vinblastine sulfate inhibits normal microtubule assembly and induces aberant tubulin polymerization causing apoptosis. This compound also inhibits autophagosome maturation.
   

   Taxol chemical structure (33069-62-4).

Microtubule stabilizing agents

1. Docetaxel (CAS# 114977-28-5) is an antimitotic chemotherapeutic with reversible high-affinity binding to microtubules. It induces apoptosis in a variety of cancer cell lines. Nevertheless, tumor cells can quickly develop resistance to docetaxel via several mechanisms.
2. Taxol (CAS# 33069-62-4) is a cancer chemotherapeutic agent (breast, non-small cell lung and ovarian cancers). It acts as a promoter of tubulin polymerization by stabilizing microtubules in vitro and in vivo leading to arrest of cells in the G2 and M phase of the cell cycle.

Looking for pure small molecules active on Microtubule and compatible with in vitro studies?

tebu-bio’s experts have selected high quality sources of active small molecules. Discover those related to tubulin and Microtubules right here.