Therapeutic use of bacteriophages

Electrocardiographic features of patients with COVID-19: One year of unexpected manifestations

N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue. We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human hydroxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase.

Combined alcoholic and non-alcoholic steatohepatitis.

Telomere maintenance is essential for protecting chromosome ends. Aberrations in telomere length have been implicated in cancer and aging. Telomere elongation by human telomerase is inhibited in cis by the telomeric protein TRF1 and its associated proteins. However, the link between TRF1 and inhibition of telomerase elongation of telomeres remains elusive because TRF1 has no direct effect on telomerase activity. We have previously identified one Pin2/TRF1-interacting protein, PinX1, that has the unique property of directly binding and inhibiting telomerase catalytic activity (Zhou, X. Z., and Lu, K. P. (2001) Cell 107, 347-359). However, nothing is known about the role of the PinX1-TRF1 interaction in the regulation of telomere maintenance. By identifying functional domains and key amino acid residues in PinX1 and TRF1 responsible for the PinX1-TRF1 interaction, we show that the TRF homology domain of TRF1 interacts with a minimal 20-amino acid sequence of PinX1 via hydrophilic and hydrophobic interactions. Significantly, either disrupting this interaction by mutating the critical Leu-291 residue in PinX1 or knocking down endogenous TRF1 by RNAi abolishes the ability of PinX1 to localize to telomeres and to inhibit telomere elongation in cells even though neither has any effect on telomerase activity per se. Thus, the telomerase inhibitor PinX1 is recruited to telomeres by TRF1 and provides a critical link between TRF1 and telomerase inhibition to prevent telomere elongation and help maintain telomere homeostasis.

We have reconstituted human mitochondrial transcription in vitro on DNA oligonucleotide templates representing the light strand and heavy strand-1 promoters using protein components (RNA polymerase and transcription factors A and B2) isolated from Escherichia coli. We show that 1 eq of each transcription factor and polymerase relative to the promoter is required to assemble a functional initiation complex. The light strand promoter is at least 2-fold more efficient than the heavy strand-1 promoter, but this difference cannot be explained solely by the differences in the interaction of the transcription machinery with the different promoters. In both cases, the rate-limiting step for production of the first phosphodiester bond is open complex formation. Open complex formation requires both transcription factors; however, steps immediately thereafter only require transcription factor B2. The concentration of nucleotide required for production of the first dinucleotide product is substantially higher than that required for subsequent cycles of nucleotide addition. In vitro, promoter-specific differences in post-initiation control of transcription exist, as well as a second rate-limiting step that controls conversion of the transcription initiation complex into a transcription elongation complex. Rate-limiting steps of the biochemical pathways are often those that are targeted for regulation. Like the more complex multisubunit transcription systems, multiple steps may exist for control of transcription in human mitochondria. The tools and mechanistic framework presented here will facilitate not only the discovery of mechanisms regulating human mitochondrial transcription but also interrogation of the structure, function, and mechanism of the complexes that are regulated during human mitochondrial transcription.

Aspirin in the prevention of cancer

Environmental and occupational allergies

Bone Marrow Iron in CKD: Correlation With Functional Iron Deficiency

Synaptic AMPA Receptor Plasticity and Behavior

Telaprevir (VX-950) is a highly selective, potent inhibitor of the hepatitis C virus (HCV) NS3.4A serine protease. It has demonstrated strong antiviral activity in patients chronically infected with genotype 1 HCV when dosed alone or in combination with peginterferon alfa-2a. Substitutions of Arg(155) of the HCV NS3 protease domain have been previously detected in HCV isolates from some patients during telaprevir dosing. In this study, Arg(155) was replaced with various residues in genotype 1a protease domain proteins and in genotype 1b HCV subgenomic replicons. Characterization of both the purified enzymes and reconstituted replicon cells demonstrated that substitutions of Arg(155) with these residues conferred low level resistance to telaprevir (<25-fold). An x-ray structure of genotype 1a HCV protease domain with the R155K mutation, in a complex with an NS4A co-factor peptide, was determined at a resolution of 2.5A. The crystal structure of the R155K protease is essentially identical to that of the wild-type apoenzyme (Protein Data Bank code 1A1R) except for the side chain of mutated residue 155. Telaprevir was docked into the x-ray structure of the R155K protease, and modeling analysis suggests that the P2 group of telaprevir loses several hydrophobic contacts with the Lys(155) side chain. It was demonstrated that replicon cells containing substitutions at NS3 protease residue 155 remain fully sensitive to interferon alpha or ribavirin. Finally, these variant replicons were shown to have reduced replication capacity compared with the wild-type HCV replicon in cells.

Unicystic ameloblastoma: a case of mistaken identity

The neuronal nitric-oxide synthase (nNOS) flavoprotein domain (nNOSr) contains regulatory elements that repress its electron flux in the absence of bound calmodulin (CaM). The repression also requires bound NADP(H), but the mechanism is unclear. The crystal structure of a CaM-free nNOSr revealed an ionic interaction between Arg(1400) in the C-terminal tail regulatory element and the 2'-phosphate group of bound NADP(H). We tested the role of this interaction by substituting Ser and Glu for Arg(1400) in nNOSr and in the full-length nNOS enzyme. The CaM-free nNOSr mutants had cytochrome c reductase activities that were less repressed than in wild-type, and this effect could be mimicked in wild-type by using NADH instead of NADPH. The nNOSr mutants also had faster flavin reduction rates, greater apparent K(m) for NADPH, and greater rates of flavin auto-oxidation. Single-turnover cytochrome c reduction data linked these properties to an inability of NADP(H) to cause shielding of the FMN module in the CaM-free nNOSr mutants. The full-length nNOS mutants had no NO synthesis in the CaM-free state and had lower steady-state NO synthesis activities in the CaM-bound state compared with wild-type. However, the mutants had faster rates of ferric heme reduction and ferrous heme-NO complex formation. Slowing down heme reduction in R1400E nNOS with CaM analogues brought its NO synthesis activity back up to normal level. Our studies indicate that the Arg(1400)-2'-phosphate interaction is a means by which bound NADP(H) represses electron transfer into and out of CaM-free nNOSr. This interaction enables the C-terminal tail to regulate a conformational equilibrium of the FMN module that controls its electron transfer reactions in both the CaM-free and CaM-bound forms of nNOS.

PDZ domains1 are modular protein interaction domains that play a role in protein targeting and protein complex assembly. Once termed Discs-large homology regions (DHRs) or GLGF repeats (after a conserved Gly-Leu-Gly-Phe sequence found within the domain), these domains of ∼90 amino acids are now primarily known by an acronym of the first three PDZ-containing proteins identified: the postsynaptic protein PSD-95/SAP90, theDrosophila septate junction protein Discs-large, and the tight junction protein ZO-1.

Rod outer segments (ROSs) are specialized light-sensitive organelles in vertebrate photoreceptor cells. Lipids in ROS are of considerable importance, not only in providing an adequate environment for efficient phototransduction, but also in originating the second messengers involved in signal transduction. ROSs have the ability to adapt the sensitivity and speed of their responses to ever-changing conditions of ambient illumination. A major contributor to this adaptation is the light-driven translocation of key signaling proteins into and out of ROS. The present review shows how generation of the second lipid messengers from phosphatidylcholine, phosphatidic acid, and diacylglycerol is modulated by the different illumination states in the vertebrate retina. Findings suggest that the light-induced translocation of phototransduction proteins influences the enzymatic activities of phospholipase D, lipid phosphate phosphatase, diacylglyceride lipase, and diacylglyceride kinase, all of which are responsible for the generation of the second messenger molecules.

We have previously shown that inhibiting protein-tyrosine kinase increased whereas inhibiting protein-tyrosine phosphatase (PTP) decreased renal outer medullary potassium channel 1 (ROMK1) channel activity (1). We have now used confocal microscopy, the patch clamp technique, and biotin labeling to further examine the role of tyrosine phosphorylation in regulating ROMK1 trafficking. Human embryonic kidney 293 cells were cotransfected with c-Src and green fluorescent protein-ROMK1, which has the same biophysical properties as those of ROMK1. Patch clamp studies have shown that phenylarsine oxide (PAO), an inhibitor of PTP, decreased the activity of ROMK1. Moreover, addition of PAO reduced the cell surface localization of green fluorescent protein-ROMK1 detected by confocal microscopy and diminished the surface ROMK1 density by 65% measured by biotin labeling. Also, PAO treatment significantly increased the phosphorylation of ROMK1. The notion that the effect of PAO is mediated by stimulating tyrosine phosphorylation-induced endocytosis of ROMK1 has also been supported by findings that mutating the tyrosine residue 337 of ROMK1 to alanine abolished the effect of PAO. Finally, the inhibitory effect of PAO on ROMK1 was completely blocked in the cells co-transfected with dominant negative dynamin (dynaminK44A). This indicates that the tyrosine phosphorylation-induced endocytosis of ROMK1 is dynamin-dependent. We conclude that inhibiting PTP increases ROMK1 phosphorylation and results in a dynamin-dependent internalization of the channel.