Coupling an alpha 2-adrenergic receptor peptide to G-protein: a new photolabeling agent

Collagen cross linking agents: design and development of a multifunctional cross linker

A new cross linking reagent based on the first-generation polyamidoamine dendrimer (G.1 PAMAM) has been synthesized by reaction of the PAMAM with eight equivalents of p-nitrophenyl diazopyruvate. The resulting water-soluble octadiazopyruvoyl PAMAM (8G.1 DAP, 1.3) was shown to undergo Wolff rearrangements upon photolysis in methanol at lambda > 300 nm to yield the methyl esters of the ketenes formed from the loss of nitrogen. 8G.1 DAP also forms strong bonds with dehydrated collagen with glass as high as 36 N cm(-2). Collagen to collagen bonds with tensile strengths as high as 92 N cm(-2) were observed with fully dehydrated tissues. The bonding decreased rapidly with increasingly hydrated tissue possibly due to the increased distance between the collagen fibrils and the competition of H2O for the free ketene functions.

Rhodopsin C terminus, the site of mutations causing retinal disease, regulates trafficking by binding to ADP-ribosylation factor 4 (ARF4)

The maintenance of photoreceptor cell polarity is compromised by the rhodopsin mutations causing the human disease autosomal dominant retinitis pigmentosa. The severe form mutations occur in the C-terminal sorting signal of rhodopsin, VXPX-COOH. Here, we report that this sorting motif binds specifically to the small GTPase ARF4, a member of the ARF family of membrane budding and protein sorting regulators. The effects of blocking ARF4 action were functionally equivalent to the effects of blocking the rhodopsin C-terminal sorting signal. ARF4 was essential for the generation of post-Golgi carriers targeted to the rod outer segments of retinal photoreceptors. Thus, the severe retinitis pigmentosa alleles that affect the rhodopsin sorting signal interfere with interactions between ARF4 and rhodopsin, leading to aberrant trafficking and initiation of retinal degeneration.

Receptor and membrane interaction sites on Gbeta. A receptor-derived peptide binds to the carboxyl terminus

The functional organization of Gbetagamma is poorly understood. Regions of bovine brain Gbetagamma that interact with a photoaffinity derivative of an alpha2-adrenergic receptor-derived peptide from the third intracellular loop (diazopyruvoyl-modified peptide Q (DAP-Q)) and a hydrophobic membrane probe (3-trifluoromethyl-3-(m-iodophenyl)diazirine (TID)) were examined. We previously showed that DAP-Q cross-links to specific, competable sites on both the alpha and beta subunits of Go/Gi but not on the gamma subunit and that betagamma subunit was required for stimulation of Go/Gi GTPase activity (Taylor, J. M., Jacob Mosier, G. G., Lawton, R. G., Remmers, A. E., and Neubig, R. R. (1994) J. Biol. Chem. 269, 27618-27624). Similarly, we show here that the membrane-associated photoprobe [125I]TID labels alpha and beta but not gamma. We have now mapped the sites of incorporation of DAP-Q and TID into the beta subunit. TID labels both the 14-kDa amino-terminal and the 23-kDa carboxyl-terminal fragments from a partial tryptic digest of beta while DAP-Q labels only the carboxyl-terminal fragment. Further mapping with endopeptidase Lys C reveals substantial labeling of multiple fragments by TID while DAP-Q labels predominantly a approximately 6-kDa fragment within the carboxyl-terminal 60 amino acids of beta1. Thus, regions within the 7th (or possibly 6th) WD-40 repeat of the beta subunit of G protein interact with the receptor-derived peptide while membrane interaction involves multiple sites throughout the beta subunit.

Identification of a domain in the angiotensin II type 1 receptor determining Gq coupling by the use of receptor chimeras

The angiotensin II type 1 (AT1R) and type 2 (AT2R) receptors belong to the seven transmembrane receptor superfamily. Previous studies have suggested that the AT1R couples to a Gq signaling pathway, whereas the AT2R does not associate with Gq. To identify the role that individual intracellular domains play in AT1R function, AT1R/AT2R chimeric receptors were prepared by substitution of intracellular loops. CHO cells expressing these chimeras were used to test angiotensin II-induced c-fos expression and Ca2+ mobilization which are involved in the AT1R signaling pathway through Gq coupling. Substitution of the second intracellular loop (IC2) and the cytoplasmic tail between the two receptors did not affect AT1R function. However, exchange of the third intracellular loop (IC3) resulted in the loss of function in the AT1R and conferred to the AT2R the ability to constitutively activate the fos promoter. These findings suggest that the third intracellular loop of the AT1R is critical for Gq coupling. Substitution of discrete amino acid sequences of the third intracellular loop indicate that its N-terminal and C-terminal portions, especially the seven amino acids 219-225 in the N-terminal portion, are important for AT1R function, and that the intermediate portion of this loop is not required for Gq coupling.