RABGGTB is the catalytic β-subunit of geranylgeranyl transferase type 3 (GGTase-3), an enzyme complex that catalyzes the transfer of geranylgeranyl moieties to Rab GTPases and other protein substrates 1. This prenylation reaction is essential for membrane localization and proper cellular function of target proteins 2. RABGGTB-mediated geranylgeranylation of Rab7 regulates autophagosome-lysosome fusion, a critical process for protein degradation 3. The enzyme also modifies the v-SNARE protein YKT6, facilitating Golgi SNARE complex assembly necessary for vesicular transport 2. Additionally, GGTase-3 geranylgeranylates FBXL2, targeting it to cellular membranes where it functions in the SCF(FBXL2) E3 ubiquitin-ligase complex 4. Disrupted RABGGTB expression is implicated in multiple neuropsychiatric and neurodegenerative diseases. Schizophrenia shows decreased RABGGTB protein levels (8% reduction) in the dorsolateral prefrontal cortex 5. Multiple sclerosis patients demonstrate significant RABGGTB downregulation, particularly in females 6. ASD is associated with RABGGTB promoter hypomethylation and increased expression in the raphe nuclei 7. RABGGTB overexpression improves autophagy and reduces protein aggregation in ALS models 3. In pancreatic β-cells, GGTase-III containing RABGGTB is essential for glucose-stimulated insulin secretion 8. These findings establish RABGGTB as a critical regulator of membrane protein function with significant implications for neurological disease pathogenesis.