Post-translational modification (PTM) of proteins is an essential cellular process used to regulate protein function and stability. PTMs are assumed to have an impact on protein structure and conformation, but the effects of specific protein conformations on biological processes are difficult to understand and test in vivo. The importance of protein conformation is of particular interest in DNA repair as many of the same proteins are involved in context specific repair processes. For example, the Mre11-Rad50-Nbs1 complex is an essential DNA double-strand break sensor that is found at every type of double-strand break. It has been proposed that this complex can, in theory, adopt up to 216 conformational states and acts as a “molecular computer” to detect damage and regulate repair pathway choice (i.e. should the break be repaired via nonhomologous end joining or homologous recombination)1. In vivo studies of the roles that particular protein conformations play are rare, yet critical for understanding the regulation of DSB repair.
New work from Steger and colleagues2 shows that Pin1, a prolyl isomerase that catalyzes cis/trans isomerization, binds multiple DNA repair proteins, including CtIP, a key player in double-strand break end resection. The authors show that the interaction between Pin1 and CtIP is induced by phosphorylation of CtIP at two S/T-Proline sites, and that Pin1 binding does indeed cause a conformational change in CtIP. This conformational change leads to polyubiquitylation of CtIP and subsequent degradation. Overexpression of Pin1 causes hyporesection and a decrease in homologous recombination; similarly, depleting Pin1 causes hyperresection and decreased NHEJ. These data and others presented in the paper lead to a model in which CtIP is phosphorylated, causing Pin1 to bind and isomerize CtIP. This isomerization leads to ubiquitin-mediated CtIP degradation and appropriate end resection. Pin1 overexpression leads to reduced CtIP activity and therefore hyporesection and decreased homologous recombination, whereas Pin1 depletion leads to increased CtIP activity, hyperresection and decreased NHEJ.
In this particular case, the researchers were lucky to find a specific protein, Pin1, that induces a known conformational change, cis/trans isomerization, by acting directly on the substrate protein. However, most conformational changes may be caused indirectly by the effects of post-translational modifications. While the identification of Pin1 as a critical regulator of DNA repair is a large step forward in understanding the role protein conformation plays in function, this same understanding for other proteins will require more cross-disciplinary studies that are able to modify protein conformation in vivo and determine the biological outcomes.
1. Williams, G. J., et al. (2010). “Mre11-Rad50-Nbs1 conformations and the control of sensing, signaling, and effector responses at DNA double-strand breaks.” DNA Repair 9(12): 1299-1306.
2. Steger, M., et al. (2013). “Prolyl Isomerase PIN1 Regulates DNA Double-Strand Break Repair by Counteracting DNA End Resection.” Molecular Cell 50(3): 333-343.
The discovery of bromodomain inhibitors and super-enhancers lead scientists to new approaches in cancer drug discovery
Cancer researchers have published innumerous papers mapping the multiple genetic mutations that exist in all cancer types. From these discoveries, hope emerged that inhibiting the mutated proteins fueling the cancer cell, or driver mutations, would lead to targeted cancer drugs. However, finding small molecule inhibitors that are successful in the clinic has proven more difficult. Within the last decade, the discovery of chromatin modifiers and their important role in various cancers provided an exciting new avenue for cancer researchers to explore. Whole genome studies of a myriad of cancers revealed numerous epigenetic regulators as driver mutations for many cancers. Nonetheless, Continue reading “New Avenues in Cancer Drug Discovery”
If you eat five portions of fruit and vegetables a day, exercise, and don’t smoke then you are well on the way to becoming an optimally functioning human. Pat on the back. Extra points if you drink alcohol within guidelines, get eight hours sleep, and don’t go on regular processed meat benders. Deduct ten points for every time you’ve stressed out, rolled giddily in asbestos, or ate your own weight in cake. Continue reading “Shake What Your Mama Gave You!”
For decades, when neuroscientists turned their attention to more complex aspects of cognition, primates have been the model animals of choice, favored for both their similarities to humans and their ability to perform intricate tasks of the sort required to probe the neural substrate of higher level mental functioning. Over the last several years, however, a wave of investigators have begun turning to the humble rodent to explore these questions. In Nature Neuroscience’s Focus on Neurotechniques this month, Carandini and Churchland examine this trend and the rewards and challenges of using rodent models to study perceptual decision making. Continue reading “Move Over, Monkeys”
Avian Influenza Transmission in Mammals
Avian influenza viruses can reassort their genomes to infect mammals. To investigate how this is done, Zhang et al. generated all possible 127 reassorted viruses by combining the hemagglutinin gene of an avian H5N1 influenza virus with an H1N1 virus capable of infecting humans. The researchers examined the virulence of these viruses in mice, as well as their ability to transmit in guinea pigs, which, like certain livestock, have both avian and mammalian airway receptors. Certain H1N1 genes allowed the H5N1 virus to transmit between guinea pigs. The virus was transferred by respiration between guinea pigs without killing them, indicating that livestock could be carriers of this virus without the farmer even knowing. Continue reading “Leafing through the Literature”
We’re more than used to drug resistance arising in bacterial pathogens. Antibiotic resistance is perhaps most well known in MRSA (methicillin-resistant Staphylococcus aureus) – a bacterial strain that had earned, through its resilience, lethality and prevalence in hospitals, the title of “super bug.” Another example is Mycobacterium tuberculosis, strains of which have (terrifyingly enough) evolved resistances to many of the weapons in our antibiotic arsenal. It’s not just bacteria that have been known to evolve such mechanisms, so today I’ll focus on another bullet dodger: malaria (caused by Plasmodium species – Plasmodium falciparum being the most dangerous). Continue reading “South East Asia and the Mystery of Malaria Resistance”
The cerebral cortex – the intricate, six layered maze of connections underlying of many of the brain’s most compex tasks – continues to offer researchers new surprises. Conventional belief holds that sensory information arrives in the cortex from the thalamus via the granular layer, layer 4, from which information is transmitted serially to layer 2/3, the main source of intracortical connections, and then to layers 5 and 6, from which arise most output to subcortical areas. A new study by Constantinople and Bruno, however, suggests that the current dogma may need to make room for a new canonical circuit Continue reading “New Insights on Cortical Circuity”
It’s that time of year when the temperatures start to rise turning closed-toed shoes into sandals and pants into shorts and we start looking out our windows 50 times a day wishing we could be outside by a pool or on a lake. Yep, I’m talking about summer, and though there is a lull in the activities occurring on campus, this is the time when a number of new faces show up on campus ranging from new doctoral students starting early to undergraduates wanting to do summer research bringing on the tidal wave of new students wanting to rotate through your lab. If you happen to be one of these new faces embarking on the journey of rotating through labs, Continue reading “A Journey into the Unknown – Lab Rotations”
An experimental TB vaccine identifies a cool new way to boost immune protection
Researchers from Canada tested out two new inhaled vaccines against adult tuberculosis, based on adenovirus or vesicular stomatitis virus. While both vaccines generated similar levels of adaptive immunity, only the adenovirus vaccine was also able to robustly activate innate immunity. Innate immunity exists in a state of constant readiness to repel pathogenic invaders, while adaptive immunity requires stimulation, activation and expansion before it can be fully engaged. Continue reading “Marvelous Microbes Round-Up”
For many researchers in biomedical sciences, the use of animal models is an integral part of daily work and crucial to advancing knowledge. While most investigators are well aware of the threat posed to such advancement by animal rights extremists, a recent editorial in Nature Neuroscience cautions that more attention should be paid to the subtler ways in which animal rights activists are impeding research, such as making it prohibitively difficult to transport research animals to institutions or pushing to ban use of individual species. Continue reading “Of Mice and Monkeys (and Scientists)”