Structure of GTP-bound L129F mutant Rab7
[RAB7A_HUMAN] Defects in RAB7A are the cause of Charcot-Marie-Tooth disease type 2B (CMT2B) [MIM:600882]; also known as hereditary motor and sensory neuropathy II (HMSN2). CMT2B is a form of Charcot-Marie-Tooth disease, the most common inherited disorder of the peripheral nervous system. Charcot-Marie-Tooth disease is classified in two main groups on the basis of electrophysiologic properties and histopathology: primary peripheral demyelinating neuropathy or CMT1, and primary peripheral axonal neuropathy or CMT2. Neuropathies of the CMT2 group are characterized by signs of axonal regeneration in the absence of obvious myelin alterations, normal or slightly reduced nerve conduction velocities, and progressive distal muscle weakness and atrophy. CMT2B is clinically characterized by marked distal muscle weakness and a high frequency of foot ulcers, infections and amputations of the toes. CMT2B inheritance is autosomal dominant.   
[RAB7A_HUMAN] Key regulator in endo-lysosomal trafficking. Governs early-to-late endosomal maturation, microtubule minus-end as well as plus-end directed endosomal migration and positioning, and endosome-lysosome transport through different protein-protein interaction cascades. Plays a central role, not only in endosomal traffic, but also in many other cellular and physiological events, such as growth-factor-mediated cell signaling, nutrient-transportor mediated nutrient uptake, neurotrophin transport in the axons of neurons and lipid metabolism. Also involved in regulation of some specialized endosomal membrane trafficking, such as maturation of melanosomes, pathogen-induced phagosomes (or vacuoles) and autophagosomes. Plays a role in the maturation and acidification of phagosomes that engulf pathogens, such as S.aureus and M.tuberculosis. Plays a role in the fusion of phagosomes with lysosomes. Plays important roles in microbial pathogen infection and survival, as well as in participating in the life cycle of viruses. Microbial pathogens possess survival strategies governed by RAB7A, sometimes by employing RAB7A function (e.g. Salmonella) and sometimes by excluding RAB7A function (e.g. Mycobacterium). In concert with RAC1, plays a role in regulating the formation of RBs (ruffled borders) in osteoclasts. Controls the endosomal trafficking and neurite outgrowth signaling of NTRK1/TRKA. Regulates the endocytic trafficking of the EGF-EGFR complex by regulating its lysosomal degradation.   
Publication Abstract from PubMed
Rab GTPases are molecular switches that orchestrate vesicular trafficking, maturation and fusion by cycling between an active, GTP-bound form, and an inactive, GDP-bound form. The activity cycle is coupled to GTP hydrolysis and is tightly controlled by regulatory proteins. Missense mutations of the GTPase Rab7 cause a dominantly inherited axonal degeneration known as Charcot-Marie-Tooth type 2B through an unknown mechanism. We present the 2.8 A crystal structure of GTP-bound L129F mutant Rab7 which reveals normal conformations of the effector binding regions and catalytic site, but an alteration to the nucleotide binding pocket that is predicted to alter GTP binding. Through extensive biochemical analysis, we demonstrate that disease-associated mutations in Rab7 do not lead to an intrinsic GTPase defect, but permit unregulated nucleotide exchange leading to both excessive activation and hydrolysis-independent inactivation. Consistent with augmented activity, mutant Rab7 shows significantly enhanced interaction with a subset of effector proteins. In addition, dynamic imaging demonstrates that mutant Rab7 is abnormally retained on target membranes. However, we show that the increased activation of mutant Rab7 is counterbalanced by unregulated, GTP hydrolysis-independent membrane cycling. Notably, disease mutations are able to rescue the membrane cycling of a GTPase-deficient mutant. Thus, we demonstrate that disease mutations uncouple Rab7 from the spatial and temporal control normally imposed by regulatory proteins and cause disease not by a gain of novel toxic function, but by misregulation of native Rab7 activity.
Disease mutations in Rab7 result in unregulated nucleotide exchange and inappropriate activation.,McCray BA, Skordalakes E, Taylor JP Hum Mol Genet. 2010 Mar 15;19(6):1033-47. Epub 2009 Dec 22. PMID:20028791
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.