Plusend

Plusend, commonly written as plus end, refers to the fast-growing end of a microtubule, a cylindrical polymer of tubulin subunits found in eukaryotic cells. Microtubules have two ends: the plus end and the minus end. The plus end is composed of β-tubulin exposed at the tip and is the primary site of polymerization and dynamic remodeling, while the minus end is typically anchored at microtubule-organizing centers such as the centrosome.

The plus end is characterized by dynamic instability, alternating between growth, shrinkage, and pauses. Growth occurs as GTP-bound tubulin adds to the end and forms a protective GTP cap; hydrolysis of GTP to GDP destabilizes the lattice, leading to rapid depolymerization or catastrophe. The end can switch back to growth via rescue events when the GDP-tubulin region is stabilized or replenished with GTP-tubulin.

Dynamic behavior is regulated by a diverse set of plus-end tracking proteins (+TIPs), including EB1, which serves as a hub for recruiting other regulators to the growing end. These proteins modulate polymerization rates, stabilize the end, link microtubules to cellular structures, and coordinate interactions with the actin cytoskeleton and motor proteins such as kinesins and dyneins.

In cellular contexts, plus-end dynamics contribute to spindle formation during mitosis, establishment of cell polarity, intracellular transport, and response to mechanical cues. Disruption of plus-end regulation is associated with defects in cell division and migration and is a target of certain anti-cancer drugs that affect microtubule stability.

The opposite end, the minus end, is typically more stable and anchored, whereas the plus end remains the primary site of behavioral regulation and remodeling of microtubules in response to cellular needs.