CCZ1 is a guanine nucleotide exchange factor (GEF) that functions as a critical component of the MON1-CCZ1 complex, regulating endosomal maturation through Rab5-to-Rab7 conversion 12. The complex catalyzes nucleotide exchange on RAB7A, enabling RAB7 activation on late endosomes and subsequent lysosomal fusion 2. Structurally, CCZ1 directly interacts with RAB7A's phosphate-binding loop, facilitating conformational changes essential for nucleotide exchange 2. CCZ1 mediates multiple cellular processes: early-to-late endosomal trafficking during filovirus infections (Marburg and Ebola), with nearly complete inhibition of viral replication upon CCZ1 disruption 3; apoptotic cell clearance through phagosome-lysosome fusion in intestinal macrophages 4; and lipid droplet catabolism via intermediate endosome formation 5. ESCRT-mediated cargo ubiquitination regulates CCZ1 recruitment timing during endosome maturation, with ubiquitinated proteins preventing RABX-5 displacement and delaying CCZ1-mediated Rab conversion 6. These functions position CCZ1 as a therapeutic target for filoviral infections and potentially inflammatory bowel disease, as impaired apoptotic clearance through CCZ1 dysfunction correlates with intestinal inflammation severity 34.