RAB2B is a protein required for protein transport from the endoplasmic reticulum to the Golgi complex. It belongs to the small GTPase superfamily, specifically to the RAB protein family[6].Small GTPases are a type of hydrolase enzymes that can attach a GTP to form a GDP. This process makes small GTPases active when bonded to a GTP and inactive when bonded to a GDP. Inside this small GTPase superfamily we can find the RAS subfamily. This family is divided into 5 groups: Ras, Rho, Ran, Rab and Arf GTPases. RAB2B is located in the RAB group. Its main function is regulating vesicle transport and membrane fusion.
Structure
RAB2B is a human protein which gene is located in the fourteenth chromosome. It has a core made of basic elements such as oxygen, carbon, nitrogen, phosphorus and magnesium. Its tertiary structure disposes the 216 amino acids this protein is made of in eight alpha helix and six beta strands. A mature RAB2B suffers three post-translational modifications, a phosposerine is found in the location 202 instead of a normal serine, and two lipidations can be found in locations 215-216. It has a motif domain between the amino acids 35 and 43. Due to the alternative splicing, two isoforms of this same protein exist. Isoform 1 is the canonical sequence, meaning it is the most common, having a molecular weight of 24,214 Da. Isoform 2 consists just in 151 amino acids, having a mass of 16,667 Da.
Biological activity
Small GTPases of the RAB superfamily are recognized as key players of the protein machinery involved in vesicular transport[7] and organelle dynamics in eukaryotic cells. RAB2B follows mainly exocytic pathways, from the endoplasmic reticulum to Golgi complex. RAB proteins are involved in docking and fusion of transport vesicles with their target membranes. These proteins associate with effector proteins (GARIL4 and GARIL5) to create complexes.
Relevance
The results of the latest research show that RAB2B isoform knockdown affected the morphology of the Golgi complex in mammls, inducing its fragmentation[8]. Even though these RAB family proteins are highly homologous to each other (RAB2A and RAB2B have 85.8% amino acid identity), the knockdown of any of them (from RAB1A to RAB8A) causes Golgi complex to disperse throgh cytoplasm. Because of this, RAB2B-deficiency affects the IFN response[9], enhancing replication of many viruses,(such as vaccinia), since the RAB2B-GARIL5 complex stops functioning properly.