Background: RhoB is down-regulated in most lung cancer cell lines and tumor tissues when compared with their normal counterparts. The mechanism of this loss of expression is not yet deciphered.

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Rho GTPases have been implicated in the control of several cellular functions, including regulation of the actin cytoskeleton, cell proliferation, and oncogenesis. Unlike RhoA and RhoC, RhoB localizes in part to endosomes and controls endocytic trafficking. Using a yeast two-hybrid screen and a glutathione S-transferase pulldown assay, we identified LC2, the light chain of the microtubule-associated protein MAP1A, as a novel binding partner for RhoB. GTP binding and the 18-amino acid C-terminal hypervariable domain of RhoB are critical for its binding to MAP1A/LC2. Coimmunoprecipitation and immunofluorescence experiments showed that this interaction occurs in U87 cells. Down-regulation of MAP1A/LC2 expression decreased epidermal growth factor (EGF) receptor expression and modified the signaling response to EGF treatment. We concluded that MAP1A/LC2 is critical for RhoB function in EGF-induced EGF receptor regulation. Because MAP1A/LC2 is thought to function as an adaptor between microtubules and other molecules, we postulate that the RhoB and MAP1A/LC2 interactions facilitate endocytic vesicle trafficking and regulate the trafficking of signaling molecules.

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The exceptionally high affinity of biotin toward avidin and streptavidin is at the basis of (strept)avidin-biotin biotechnology, which has numerous applications in life sciences. Recent biotin developments for in vivo and in vitro acylation of selective targeted protein and intein-mediated site specific protein biotinylation require the free biotin carboxyl function to covalently bind with the targeted protein. However, recently this carboxylic function has been used to substitute biotin with numerous ligands and flags. In the present work, we propose the N-1' labeling possibilities of biotin, keeping the valeric chain free. We describe liquid and solid-phase syntheses of functionalized biotin N-1' derivatives. Although the N-1' modification involves a two-log decrease in affinity, in vitro these molecules kept their high avidin affinity (around 10(-12) M) and the in vivo acylation ability of new biotin derivatives.

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