Ahmed Zahraoui

The Product of rab2, a Small GTP Binding Protein, Increases Neuronal Adhesion, and Neurite Growth In Vitro

The rab genes code for small GTP binding proteins that share with p21ras the ability to bind and hydrolyze GTP. They present significant sequence homologies with the products of YPT1 and SEC4, two small GTP binding proteins involved in the regulation of secretion in the yeast. Several rab genes are expressed in the developing and adult mouse brain. To test directly the possible involvement of these genes in neuronal differentiation, purified rab proteins produced in E. coli were introduced into neurons dissociated from E15 rat midbrain. The most striking effects were obtained with rab2 protein (rab2p). Compared with untreated cells, neurons loaded with rab2p presented an enhanced adhesion to the culture substratum. This phenomenon was visible 3 hr after seeding and was followed within 24 hr by a dramatic increase in neurite growth. Loading the same population of neurons with the products of four other rab genes either decreased neuronal adhesion and neurite growth or had no effect. These experiments suggest that the expression of rab2p plays an important role in neuronal differentiation.

Isoprenylation of Rab proteins possessing a C-terminal CaaX motif

Rab proteins are small GTPases highly related to the yeast Ypti and Sec4 proteins involved in secretion. The Rab proteins were found associated with membranes of different compartments along the secretory and endocytic pathways. They share distinct C‐terminal cysteine motifs required for membrane association. Unlike the other Rab proteins, Rab8, Rab11 and Rab13 terminate with a C‐terminal CaaX motif similar to those of Ras/Rho proteins. This report demonstrates that Rab8 and Rab13 proteins are isoprenylated in vivo and geranylgeranylated in vitro. Rab11 associates in vitro geranylgeranylpyrophosphate and farnesylpyrophosphate. Our study shows that the CaaX motif is required for isoprenylation.

The HIV-1 protein Vpr impairs phagosome maturation by controlling microtubule-dependent trafficking

The HIV protein Vpr interacts with EB1, p150Glued, and dynein heavy chain and perturbs the centripetal movement of phagosomes and their maturation, resulting in impaired phagolysosome biogenesis, which is important for bacterial clearance and cytokine production.

Localization of the ras-like rab3A protein in the adult rat brain.

Rab3A is a small GTP-binding synaptic vesicle protein, shown to dissociate from synaptic vesicle membranes upon depolarization-induced exocytosis. Using an antiserum raised against rab3A, we found that the antigen was localized to the neuropil of specific brain regions, but was not present in major fiber tracts or most cell bodies. For example, the neuropil of several thalamic nuclei (i.e., dorsal lateral geniculate nucleus, lateral posterior nucleus, ventroposterior nucleus), cerebral cortex, upper layers of the superior colliculus and matrix zones of the neostriatum, were strongly immunoreactive, while the anterior commissure, corpus callosum, optic tract and internal capsule were devoid of staining. The hippocampus, regions of cerebral cortex and the cerebellum exhibited striking laminar distributions of rab3A immunoreactivity. In the hippocampus, dark staining was observed in the stratum oriens, stratum radiatum and molecular layer of the dentate gyrus, while the pyramidal, stratum lacunosum moleculare and dentate granule layers were not stained. In cerebellum the molecular layer and to a lesser extent, the underlying granule cell layer showed enhanced immunoreactivity. Seven days after excitotoxic lesions of the cerebral cortex, rab3A immunoreactivity was diminished in the mirror locus in the contralateral cortical hemisphere and in certain thalamic nuclei ipsilateral to the injection site. These results show that rab3A is localized to a number of specific regions. Its absence from other areas suggests that this synaptic vesicle protein is not universal to all neuronal terminals and pathways. In addition, our lesion studies indicate that for some brain regions, much of the antigen originates in cortical neurons and is distributed within specific axonal projections.

Chromosome assignment of four RAS-related RAB genes

SummaryThe human RAB genes share structural and biochemical properties with the RAS gene superfamily. The encoded RAB proteins show 38 to 75% amino acid identity with the yeast YPT1 and SEC4 gene products. We used four human RAB-cDNAs, RAB3B, RAB4, RAB5 and RAB6, to map the corresponding genes on human chromosomes. These genes were assigned to 1p32-p31, 1q42-q43, 3p24-p22 and 2q14-q21, respectively, by in situ hybridization.

Biochemical properties of the YPT-related rab1B protein: Comparison with rab1A

GTP binding protein; Superfamily, ras; Secretion

Chromosome mapping of the human ras-related rab3A gene to 19p13.2

The rab genes belong to one of the three main branches of the ras super family. The encoded rab proteins share 38 to 75% amino acid identity with the yeast YPT1 and SEC4 proteins. We used the human rab3A cDNA to map the corresponding gene on human chromosomes by chromosome sorting and in situ hybridization. Both techniques allowed the assignment of the rab3A gene to chromosome 19 with a regional localization on 19p13.2 obtained by in situ hybridization.

Expression of the small GTP-binding protein Rab3A in the adult rat brain.

The ras-related rab genes code for small GTP-binding proteins that are thought to control intracellular membrane trafficking. Some of the rab proteins are localized to the membrane of specific subcellular organelles, and rab3A is associated with small synaptic vesicles. We have studied rab3A mRNA expression in the adult rat brain by in situ hybridization. In the forebrain, rab3A mRNAs were mostly detected in neocortical and limbic areas such as hippocampus, enthorinal cortex, or rhinencephalic nuclei, while no significant labeling was observed in the striatum, in the hypothalamus, or in several thalamic nuclei. Rab3A expression does not directly correspond to any known neurotransmitter expression pattern nor is it completely superimposable to the pattern of expression of other synaptic vesicle proteins. These results show that rab3A is expressed and thus exerts its function in a subset of neurons in the brain.

Structure of the Human ras Gene Family

To study the structure of the ras gene family, we devised an original oligonucleotide strategy and isolated cDNAs for several new ras-related proteins: the ra1A protein (50% a.a. identity with ras) and the rab proteins, related to the yeast YPT and SEC4 proteins. These new isolates, as well as drosophila D-ras3 and rho probes were then used to precise the structure of the ras family, in human.

STRUCTURE AND ORGANIZATION OF THE RAS GENE FAMILY, IN HUMAN

The H-ras, K-ras and N-ras genes code for 21kd GTP/GDP binding proteins possessing a weak GTPase activity and transiently anchored to the inner face of the plasma membrane by a palmitic acid covalently linked to their C-terminus.