Regulation of sensory neuron-specific acid-sensing ion channel 3 by the adaptor protein Na+/H+ exchanger regulatory factor-1

Acid-sensing ion channels (ASICs) are cationic channels activated by extracellular protons. The ASIC3 subunit is largely expressed in the peripheral nervous system, where it contributes to pain perception and to some aspects of mechanosensation. We report here a PDZ-dependent and protein kinase C-modulated association between ASIC3 and the Na+/H+ exchanger regulatory factor-1 (NHERF-1) adaptor protein. We show that NHERF-1 and ASIC3 are co-expressed in dorsal root ganglion neurons. NHERF-1 enhances the ASIC3 peak current in heterologous cells, including F-11 dorsal root ganglion cells, by increasing the amount of channel at the plasma membrane. Perhaps more importantly, we show that the plateau current of ASIC3 can be dramatically increased (10-30-fold) by association with NHERF-1, leading to a significant sustained current at pH 6.6. In the presence of NHERF-1, the ASIC3 subcellular localization is modified, and the channel co-localizes with ezrin, a member of the ezrin-radixin-moesin family of actin-binding proteins, providing the first direct link between ASIC3 and the cortical cytoskeleton. Given the importance of the ASIC3 sustained current in nociceptor excitability, it is likely that NHERF-1 participates in channel functions associated with nociception and mechanosensation.     

An enzyme-coupled continuous spectrophotometric assay for S-adenosylmethionine-dependent methyltransferases

Modification of small molecules and proteins by methyltransferases affects a wide range of biological processes. Here, we report an enzyme-coupled continuous spectrophotometric assay to quantitatively characterize S-adenosyl-L-methionine (AdoMet/SAM)-dependent methyltransferase activity. In this assay, S-adenosyl-L-homocysteine (AdoHcy/SAH), the transmethylation product of AdoMet-dependent methyltransferases, is hydrolyzed to S-ribosylhomocysteine and adenine by recombinant S-adenosylhomocysteine/5'-methylthioadenosine nucleosidase (SAHN/MTAN, EC 3.2.2.9). Subsequently, adenine generated from AdoHcy is further hydrolyzed to hypoxanthine and ammonia by recombinant adenine deaminase (EC 3.5.4.2). This deamination is associated with a decrease in absorbance at 265 nm that can be monitored continuously. Coupling enzymes are recombinant and easily purified. The utility of this assay was shown using recombinant rat protein arginine N-methyltransferase 1 (PRMT1, EC 2.1.1.125), which catalyzes the mono- and dimethylation of guanidino nitrogens of arginine residues in select proteins. Using this assay, the kinetic parameters of PRMT1 with three synthetic peptides were determined. An advantage of this assay is the destruction of AdoHcy by AdoHcy nucleosidase, which alleviates AdoHcy product feedback inhibition of S-adenosylmethionine-dependent methyltransferases. Finally, this method may be used to assay other enzymes that produce AdoHcy, 5'-methylthioadenosine, or compounds that can be cleaved by AdoHcy nucleosidase.     

Primary empty sella with isolated ACTH deficiency and microprolactinoma

The empty sella turcica is defined as the herniation of the subarachnoid space within the sella with displacement of the pituitary towards the posteroinferior wall. By autopsy studies, the incidence in the general population is around 20%. The association of prolactinoma and empty sella has been coincidental & infrequently reported. As such for microadenoma, visual field testing and screening for hypopituitarism is not needed, but if it is associated with empty sella, both visual field testing and screening for hypopituitarism is necessary.     

Assays for RNA synthesis and replication by the hepatitis C virus

At least six major genotypes of Hepatitis C virus (HCV) cause liver diseases worldwide.The efficacy rates with current standard of care are about 50％ against genotype 1,the most prevalent strain in the...     

Substrate profiling of PRMT1 reveals amino acid sequences that extend beyond the "RGG" paradigm

Protein arginine methyltransferase 1 (PRMT1) catalyzes the mono- and dimethylation of certain protein arginine residues. Although this posttranslational modification has been implicated in many physiological processes, the molecular basis for PRMT1 substrate recognition is poorly understood. Most modified arginine residues in known PRMT1 substrates reside in repeating "RGG" sequences. However, PRMT1 also specifically methylates Arg3 of histone H4 in a region that is not glycine-arginine rich, suggesting that PRMT1 substrates are not limited to proteins bearing "RGG" sequences. Because a systematic evaluation of PRMT1 substrate specificity has not been performed, it is unclear if the "RGG" sequence accurately represents the consensus target for PRMT1. Using a focused peptide library based on a sequence derived from the in vivo substrate fibrillarin we observed that PRMT1 methylated substrates that had amino acid residues other than glycine in the "RX (1)" and "RX (1)X (2)" positions. Importantly, eleven additional PRMT1 substrate sequences were identified. Our results also illustrate that the two residues on the N-terminal side of the modification site are important and need not both be glycine. PRMT1 methylated the eukaryotic initiation factor 4A1 (eIF4A1) protein, which has a single "RGG" sequence. Methylation of eIF4A1 and the similar eIF4A3 could be affected using single site mutations adjacent to the modification site, demonstrating the importance of amino acid sequence in PRMT1 protein substrates. Dimethylation of the parent library peptide was shown to occur through a dissociative mechanism. In summary, PRMT1 selectively recognizes a set of amino acid sequences in substrates that extend beyond the "RGG" paradigm.     

Prevalence of Cholera Toxin Genes (ctxA and zot) among Non-O1/O139 Vibrio cholerae Strains from Newport Bay, California

The examination of 137 non-O1/O139 Vibrio cholerae isolates from Newport Bay, California, indicated the presence of diverse genotypes and a temporal succession. Unexpectedly, the cholera toxin gene (ctxA) was found in 17% of the strains, of which one-third were also positive for the zot gene. This suggests that ctxA is prevalent in the region of nonepidemicity and is likely to have an environmental origin.