Role of Amino Acid Side Chains in Region 17–31 of Parathyroid Hormone (PTH) in Binding to the PTH Receptor

The principal receptor-binding domain (Ser(17)-Val(31)) of parathyroid hormone (PTH) is predicted to form an amphiphilic alpha-helix and to interact primarily with the N-terminal extracellular domain (N domain) of the PTH receptor (PTHR). We explored these hypotheses by introducing a variety of substitutions in region 17-31 of PTH-(1-31) and assessing, via competition assays, their effects on binding to the wild-type PTHR and to PTHR-delNt, which lacks most of the N domain. Substitutions at Arg(20) reduced affinity for the intact PTHR by 200-fold or more, but altered affinity for PTHR-delNt by 4-fold or less. Similar effects were observed for Glu substitutions at Trp(23), Leu(24), and Leu(28), which together form the hydrophobic face of the predicted amphiphilic alpha-helix. Glu substitutions at Arg(25), Lys(26), and Lys(27) (which forms the hydrophilic face of the helix) caused 4-10-fold reductions in affinity for both receptors. Thus, the side chains of Arg(20), together with those composing the hydrophobic face of the ligand's putative amphiphilic alpha-helix, contribute strongly to PTHR-binding affinity by interacting specifically with the N domain of the receptor. The side chains projecting from the opposite helical face contribute weakly to binding affinity by different mechanisms, possibly involving interactions with the extracellular loop/transmembrane domain region of the receptor. The data help define the roles that side chains in the binding domain of PTH play in the PTH-PTHR interaction process and provide new clues for understanding the overall topology of the bimolecular complex

Site-directed Mutagenesis of Evolutionary Conserved Carboxylic Amino Acids in the Chitosanase from Streptomyces sp. N174 Reveals Two Residues Essential for Catalysis

The comparison of four sequences of prokaryotic chitosanases, belonging to the family 46 of glycosyl hydrolases, revealed a conserved N-terminal module of 50 residues, including five invariant carboxylic residues. To verify if some of these residues are important for catalytic activity in the chitosanase from Streptomyces sp. N174, these 5 residues were replaced by site-directed mutagenesis. Substitutions of Glu-22 or Asp-40 with sterically conservative (E22Q, D40N) or functionally conservative (E22D, D40E) residues reduced drastically specific activity and kcat, while Km− was only slightly changed. The other residues examined, Asp-6, Glu-36, and Asp-37, retained significant activity after mutation. Circular dichroism studies of the mutant chitosanases confirmed that the observed effects are not due to changes in secondary structure. These results suggested that Glu-22 and Asp-40 are directly involved in the catalytic center of the chitosanase and the other residues are not essential for catalytic activity

Mapping far-IR emission from the central kiloparsec of NGC 1097

Using photometry of NGC 1097 from the Herschel PACS (Photodetector Array Camera and Spectrometer) instrument, we study the resolved properties of thermal dust continuum emission from a circumnuclear starburst ring with a radius ~ 900 pc. These observations are the first to resolve the structure of a circumnuclear ring at wavelengths that probe the peak (i.e. lambda ~ 100 micron) of the dust spectral energy distribution. The ring dominates the far-infrared (far-IR) emission from the galaxy - the high angular resolution of PACS allows us to isolate the ring's contribution and we find it is responsible for 75, 60 and 55% of the total flux of NGC 1097 at 70, 100 and 160 micron, respectively. We compare the far-IR structure of the ring to what is seen at other wavelengths and identify a sequence of far-IR bright knots that correspond to those seen in radio and mid-IR images. The mid- and far-IR band ratios in the ring vary by less than +/- 20% azimuthally, indicating modest variation in the radiation field heating the dust on ~ 600 pc scales. We explore various explanations for the azimuthal uniformity in the far-IR colors of the ring including a lack of well-defined age gradients in the young stellar cluster population, a dominant contribution to the far-IR emission from dust heated by older (> 10 Myr) stars and/or a quick smoothing of local enhancements in dust temperature due to the short orbital period of the ring. Finally, we improve previous limits on the far-IR flux from the inner ~ 600 pc of NGC 1097 by an order of magnitude, providing a better estimate of the total bolometric emission arising from the active galactic nucleus and its associated central starburst.Comment: Accepted for publication in the A&A Herschel Special Editio

A Study of Heating and Cooling of the ISM in NGC 1097 with Herschel-PACS and Spitzer-IRS

NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar and an active nucleus. We present a detailed study of the spatial variation of the far infrared (FIR) [CII]158um and [OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with [CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in the Enuc S. SED modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high intensity photodissociation regions (PDRs), in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the the H2 emission in the starburst ring could come from warm regions in the diffuse ISM that are heated by turbulent dissipation or shocks.Comment: 17 pages, 14 figures, 5 tables; accepted for publication in Ap

Multiplicity in cellulases of Schizophyllum commune - derivation partly from heterogeneity in transcription and glycosylation

Peer reviewed: YesNRC publication: Ye

The 5S RNA binding protein from yeast (Saccharomyces cerevisiae) ribosomes. Evolution of the eukaryotic 5S RNA binding protein

Peer reviewed: YesNRC publication: Ye