Rab33B

Rab33B is a member of the Rab family of small GTPases that regulate vesicular trafficking in eukaryotic cells. In humans, the Rab33B protein is encoded by the RAB33B gene. It localizes primarily to the Golgi apparatus, where it participates in intra-Golgi transport and helps coordinate the movement of cargo between Golgi cisternae.

Rab33B functions as a molecular switch. In its active GTP-bound form it binds to specific effector proteins that promote tethering and fusion of transport vesicles, enabling orderly cargo sorting and processing as proteins move through the Golgi. Inactivation occurs when the GTP is hydrolyzed to GDP. The cycling between active and inactive states is controlled by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs).

Rab33B is one of two human Rab33 paralogs, Rab33A and Rab33B, and is distinguished by its Golgi localization and involvement in intra-Golgi transport. The precise complement of interactors and readers of Rab33B continues to be explored, but it is generally considered a contributor to maintaining Golgi stack organization and efficient cargo processing.

Mutations or dysregulation of Rab GTPases can affect trafficking pathways, and Rab33B is studied as part of the broader understanding of Golgi function and intracellular transport. Its activity is commonly investigated in cell biology to illuminate the mechanisms governing vesicle tethering, fusion, and Golgi morphology.