Biomedical subjects

Valérie Derrien

Publications and source records attributed to Valérie Derrien.

3 recordsLinked to original sources

PubMed2005

Specific triazine resistance in bacterial reaction centers induced by a single mutation in the QA protein pocket.

We report here the first example of a reaction center mutant from Rhodobacter sphaeroides, where a single mutation (M266His --> Leu) taking place in the primary quinone protein pocket confers selective resistance to triazine-type inhibitors (terbutryn, ametryn, and atrazine), which bind in the secondary quinone protein pocket, at about 13 A from the mutation site. The M266His --> Leu mutation involves one of the iron atom ligands. Interestingly, neither the secondary quinone nor the highly specific inhibitor stigmatellin binding affinities are affected by the mutation. It is noticeable that in the M266His --> Ala mutant a nativelike behavior in observed. We suggest that the long side chain of Leu in position M266 may lack space to accommodate in the Q(A) pocket therefore transferring its hindrance to the Q(B) pocket. This may occur via the structural feature formed by the Q(A)-M219His-Fe-L190His-inhibitor (or Q(B)) connection, pushing L189Leu and/or L229Ile in closer contact to the triazine molecules, therefore decreasing their bindings. This opens the possibility to finely tune, in reaction center proteins, the affinity for herbicides by designing mutations distant from their binding sites.

Atrazine↗

PubMed2003

ARF6 controls post-endocytic recycling through its downstream exocyst complex effector.

The small guanosine triphosphate (GTP)-binding protein ADP-ribosylation factor (ARF) 6 regulates membrane recycling to regions of plasma membrane remodeling via the endocytic pathway. Here, we show that GTP-bound ARF6 interacts with Sec10, a subunit of the exocyst complex involved in docking of vesicles with the plasma membrane. We found that Sec10 localization in the perinuclear region is not restricted to the trans-Golgi network, but extends to recycling endosomes. In addition, we report that depletion of Sec5 exocyst subunit or dominant inhibition of Sec10 affects the function and the morphology of the recycling pathway. Sec10 is found to redistribute to ruffling areas of the plasma membrane in cells expressing GTP-ARF6, whereas dominant inhibition of Sec10 interferes with ARF6-induced cell spreading. Our paper suggests that ARF6 specifies delivery and insertion of recycling membranes to regions of dynamic reorganization of the plasma membrane through interaction with the vesicle-tethering exocyst complex.

ADP-Ribosylation Factor 6↗

PubMed2002

A conserved C-terminal domain of EFA6-family ARF6-guanine nucleotide exchange factors induces lengthening of microvilli-like membrane protrusions.

We recently reported the identification of EFA6 (exchange factor for ARF6), a brain-specific Sec7-domain-containing guanine nucleotide exchange factor that works specifically on ARF6. Here, we have characterized the product of a broadly expressed gene encoding a novel 1056 amino-acid protein that we have named EFA6B. We show that EFA6B, which contains a Sec7 domain that is highly homologous to EFA6, works as an ARF6-specific guanine exchange factor in vitro. Like EFA6, which will be referred to as EFA6A from now on, EFA6B is involved in membrane recycling and colocalizes with ARF6 in actin-rich membrane ruffles and microvilli-like protrusions on the dorsal cell surface in transfected baby hamster kidney cells. Strikingly, homology between EFA6A and EFA6B is not limited to the Sec7 domain but extends to an adjacent pleckstrin homology (PH) domain and a approximately 150 amino-acid C-terminal region containing a predicted coiled coil motif. Association of EFA6A with membrane ruffles and microvilli-like structures depends on the PH domain, which probably interacts with phosphatidylinositol 4,5-biphosphate. Moreover, we show that overexpression of the PH domain/C-terminal region of EFA6A or EFA6B in the absence of the Sec7 domain promotes lengthening of dorsal microvillar protrusions. This morphological change requires the integrity of the coiled-coil motif. Lastly, database analysis reveals that the EFA6-family comprises at least four members in humans and is conserved in multicellular organisms throughout evolution. Our results suggest that EFA6 family guanine exchange factors are modular proteins that work through the coordinated action of the catalytic Sec7 domain to promote ARF6 activation, through the PH domain to regulate association with specific subdomains of the plasma membrane and through the C-terminal region to control actin cytoskeletal reorganization.

ADP-Ribosylation Factor 6↗