Effect of cholesterol nanodomains on monolayer morphology and dynamics
KyuHan Kim, Siyoung Q. Choi, Zachary A. Zell, Todd M. Squires, and Joseph A. Zasadzinski
Replacement lung surfactants have dramatically reduced premature infant mortality owing to respiratory distress syndrome. However, clinical lung surfactant varies widely in composition, and even the existence of cholesterol in native lung surfactants remains controversial. Improving replacement surfactants will require an understanding of each molecular component’s role in a film’s static and dynamic properties. Here (pp. E3054–E3060), we show that small cholesterol fractions reduce the viscosity of model lung surfactant interfaces by orders of magnitude while leaving compressibility and collapse unchanged, offering control over surfactant spreadability. Lipid–cholesterol nanodomain complexes are observed, which act as line-active sources of free area to reduce surface viscosity.
Microsatellite-encoded domain in rodent Sry functions as a genetic capacitor to enable the rapid evolution of biological novelty
Yen-Shan Chen, Joseph D. Racca, Paul W. Sequeira, Nelson B. Phillips, and Michael A. Weiss
Gene duplication is prominent among evolutionary pathways through which novel transcription factors and gene regulatory networks evolve. A model in mammals is provided by Sry, a Y-encoded Sox factor that initiates male development. We provide evidence (pp. E3061–E3070) that a CAG DNA microsatellite invasion into the Sry gene of a rodent superfamily enabled its rapid evolution. This unstable microsatellite encodes a variable length glutamine-rich repeat domain. Our results suggest that intragenic complementation between the glutamine-rich domain and canonical Sry motifs accelerated their divergence through repeat length–dependent biochemical linkages. Such novelty may underlie emergence of non–Sry-dependent mechanisms of male sex determination.
Insight into mechanisms of 3′-5′ exonuclease activity and removal of bulky 8,5′-cyclopurine adducts by apurinic/apyrimidinic endonucleases
Abdelghani Mazouzi, Armelle Vigouroux, Bulat Aikeshev, Philip J. Brooks, Murat K. Saparbaev, Solange Morera, and Alexander A. Ishchenko
Oxidative DNA damage has been postulated to play an important role in human neurodegenerative disorders and cancer. 8,5′-cyclo-2′-deoxyadenosine (cdA) is generated in DNA by hydroxyl radical attack and strongly blocks DNA replication and transcription. Here (pp. E3071–E3080) we demonstrate that cdA adducts at 3′ termini of DNA can be removed by 3′-5′ exonuclease activity of the apurinic/apyrimidinic (AP) endonucleases: Escherichia coli Xth and human APE1. The crystal structure of bacterial AP endonuclease in complex with DNA duplex provides insight into the mechanism of this activity. This new repair function provides an alternative pathway to counteract genotoxic effect of helix-distorting DNA lesions.
Mod5 protein binds to tRNA gene complexes and affects local transcriptional silencing
Matthew Pratt-Hyatt, Dave A. Pai, Rebecca A. Haeusler, Glenn G. Wozniak, Paul D. Good, Erin L. Miller, Ian X. McLeod, John R. Yates III, Anita K. Hopper, and David R. Engelke
This study (pp. E3081–E3089) provides new insight into the requirements for observed silencing of RNA polymerase II transcription near tRNA genes. Mod5 is a conserved tRNA modification enzyme found in both the nucleus and cytoplasm, although it only modifies tRNAs in the cytoplasm. Mod5 is required for silencing near tRNA genes, and it is bound to both nuclear tRNA gene complexes and nuclear pre-tRNA transcripts. Possible mechanisms for this form of RNA-mediated transcriptional silencing are discussed.
Prereplicative repair of oxidized bases in the human genome is mediated by NEIL1 DNA glycosylase together with replication proteins
Muralidhar L. Hegde, Pavana M. Hegde, Larry J. Bellot, Santi M. Mandal, Tapas K. Hazra, Guo-Min Li, Istvan Boldogh, Alan E. Tomkinson, and Sankar Mitra
Repair of mutagenic oxidized bases in the genome is required before replication to prevent mutations. It is unknown how such base lesions, which do not block replication, are flagged for repair in the single-stranded replicating template. We demonstrate here (pp. E3090–E3099) that the repair-initiating, S-phase–activated Nei-like (NEIL) 1 DNA glycosylase binds to but does not excise the base lesion and cleave the template DNA strand, which would lead to a lethal double-strand break. Instead, NEIL1 blocks progression of the replication fork, which then regresses to allow lesion repair. In the absence of NEIL1, the related glycosylase NEIL2 serves as a backup enzyme.
Protective effect of mitochondria-targeted antioxidants in an acute bacterial infection
Egor Y. Plotnikov, Maria A. Morosanova, Irina B. Pevzner, Ljubava D. Zorova, Vasily N. Manskikh, Natalya V. Pulkova, Svetlana I. Galkina, Vladimir P. Skulachev, and Dmitry B. Zorov
The main approach to treat acute pyelonephritis is antibiotic therapy. However, the pathology is accompanied by inflammation and oxidative stress phenomena that can also be a target for intervention when direct antibacterial measures are impossible or inefficient. In our study (pp. E3100–E3108), in vitro and in vivo models of experimental pyelonephritis were used to define the role of mitochondria in this pathology and to find a way to alleviate the kidney damage. The majority of the deleterious effects of pyelonephritis, including animal mortality in extreme cases, were prevented by the treatment with the mitochondria-targeted antioxidant, pointing to mitochondria as a therapeutic target.
Interferon-induced RIP1/RIP3-mediated necrosis requires PKR and is licensed by FADD and caspases
Roshan J. Thapa, Shoko Nogusa, Peirong Chen, Jenny L. Maki, Anthony Lerro, Mark Andrake, Glenn F. Rall, Alexei Degterev, and Siddharth Balachandran
The interferons are small secreted proteins with powerful antiviral and cytotoxic properties. Here (pp. E3109–E3118), we outline a signaling pathway activated by interferons that results in the precipitous necrotic death of susceptible cells. Interferon-induced necrosis proceeds via a novel, progressive mechanism that requires RNA transcription, as well as the sequential activity of three serine-threonine kinases: PKR, RIP1, and RIP3. This pronecrotic kinase cascade is normally held in check by FADD and caspases. As FADD can be disabled by phosphorylation during mitosis, our findings suggest the existence of a putative cell cycle-dependent checkpoint that licenses interferon-induced necrosis.
MAIT cells are critical for optimal mucosal immune responses during in vivo pulmonary bacterial infection
Anda Meierovics, Wei-Jen Chua Yankelevich, and Siobhán C. Cowley
Mucosa-associated invariant T (MAIT) cells are an innate T-cell subset uniquely activated by microbe-derived vitamin B metabolites. Thus far, little is known about MAIT cell contributions to defense against pathogens in vivo. Using murine respiratory tularemia as a model of mucosal infection, we show (pp. E3119–E3128) that MAIT cells are required for the prompt initiation of immune responses in the lungs. Surprisingly, MAIT cells also actively contributed to immunity throughout the later stages of infection. Thus, MAIT cells are a unique T-cell subset with wide-ranging activities that may be harnessed to improve future vaccines and adjuvants used at mucosal surfaces.
Metagenomic natural product discovery in lichen provides evidence for a family of biosynthetic pathways in diverse symbioses
Annette Kampa, Andrey N. Gagunashvili, Tobias A. M. Gulder, Brandon I. Morinaka, Cristina Daolio, Markus Godejohann, Vivian P. W. Miao, Jörn Piel, and Ólafur S. Andrésson
Remarkable chemical families are being recognized by studying diverse symbioses. We identified (pp. E3129–E3137), through metagenomics, the first cyanobacterial trans-AT polyketide biosynthetic pathway in the Nostoc symbiont of the lichen Peltigera membranacea and showed its expression in natural thalli. An isotope-based technique designed for characterizing minute amounts of material confirmed predictions that its product, nosperin, is a distinct member of the pederin family of compounds that was previously thought exclusive to animal–bacteria associations. The unexpected discovery of nosperin in lichen expands the structural range and known distribution of this family of natural products and suggests a role associated with symbiosis.
Heparan sulfate proteoglycans mediate internalization and propagation of specific proteopathic seeds
Brandon B. Holmes, Sarah L. DeVos, Najla Kfoury, Mei Li, Rachel Jacks, Kiran Yanamandra, Mohand O. Ouidja, Frances M. Brodsky, Jayne Marasa, Devika P. Bagchi, Paul T. Kotzbauer, Timothy M. Miller, Dulce Papy-Garcia, and Marc I. Diamond
Prion-like propagation of proteopathic seeds may underlie the progression of neurodegenerative diseases, including the tauopathies and synucleinopathies. Aggregate entry into the cell is a crucial step in transcellular propagation. We used (pp. E3138–E3147) chemical, enzymatic, and genetic methods to identify heparan sulfate proteoglycans as critical mediators of tau aggregate binding and uptake, and subsequent seeding of normal intracellular tau. This pathway mediates aggregate uptake in cultured cells, primary neurons, and brain. α-Synuclein fibrils use the same entry mechanism to seed intracellular aggregation, whereas huntingtin fibrils do not. This establishes the molecular basis for a key step in aggregate propagation.