Plasma membrane association by N-acylation governs PKG function in Toxoplasma gondii

ABSTRACT Cyclic GMP (cGMP)-dependent protein kinase (protein kinase G [PKG]) is essential for microneme secretion, motility, invasion, and egress in apicomplexan parasites, However, the separate roles of two isoforms of the kinase that are expressed by some apicomplexans remain uncertain. Despite having identical regulatory and catalytic domains, PKG I is plasma membrane associated whereas PKG II is cytosolic in Toxoplasma gondii . To determine whether these isoforms are functionally distinct or redundant, we developed an auxin-inducible degron (AID) tagging system for conditional protein depletion in T. gondii . By combining AID regulation with genome editing strategies, we determined that PKG I is necessary and fully sufficient for PKG-dependent cellular processes. Conversely, PKG II is functionally insufficient and dispensable in the presence of PKG I . The difference in functionality mapped to the first 15 residues of PKG I , containing a myristoylated Gly residue at position 2 that is critical for membrane association and PKG function. Collectively, we have identified a novel requirement for cGMP signaling at the plasma membrane and developed a new system for examining essential proteins in T. gondii . IMPORTANCE Toxoplasma gondii is an obligate intracellular apicomplexan parasite and important clinical and veterinary pathogen that causes toxoplasmosis. Since apicomplexans can only propagate within host cells, efficient invasion is critically important for their life cycles. Previous studies using chemical genetics demonstrated that cyclic GMP signaling through protein kinase G (PKG)-controlled invasion by apicomplexan parasites. However, these studies did not resolve functional differences between two compartmentalized isoforms of the kinase. Here we developed a conditional protein regulation tool to interrogate PKG isoforms in T. gondii . We found that the cytosolic PKG isoform was largely insufficient and dispensable. In contrast, the plasma membrane-associated isoform was necessary and fully sufficient for PKG function. Our studies identify the plasma membrane as a key location for PKG activity and provide a broadly applicable system for examining essential proteins in T. gondii . </jats:p

The Rise of China Through the Lens of Realism

China has experienced drastic growth on a number of fronts over the course of the last several decades. As a military contender, an economic player, and a political influencer, China has risen to become one of the top power in the world. China’s transformation has become a topic of discussion in the scholarly community and well beyond. In the recent United States’ Presidential Election, Mitt Romney and Barack Obama extensively discussed the importance of China in the international system and how the United States ought to respond. China’s significance in international affairs has been recognized not only by political leaders and media; China has become a large part of conversation amongst international relations theorists as well. Of the scholarly work that has been done on the rise of China, the international relations theory of realism has received a large amount of attention. The research and corresponding literature review that I have undertaken attempts to display the various efforts by realist scholars to analyze the current and future state of China. Additionally, my review portrays the differences between scholars as well as the strengths and shortcomings of their respective arguments. The research included in this endeavor includes, but is not limited to, an analysis of how neo-realism, classical realism, and neoclassical realism perceive China and how they will interact with the international community in the future. The review provides an in-depth case study on how the various tenets of realism apply directly to one of the biggest international topics of the 21st century: the rise of China

The University in the 1990s: Crisis or Predicament?

The financial difficulties which our universities are currently encountering are not without precedent, as a brief retrospective look at conditions in the 1930s will attest. However, the "decision space " in which we must operate today is far more circumscribed than at any time in the past. External constraints continue to increase in number and severity; the contemporary academic culture has greatly weakened old institutional values and identities; and governance structures have become inordinately complex, cumbersome, and ill-adapted to deal with existing realities. In these circumstances, strident demands for "greater accountability " and "stronger leadership " cannot really be met. It is imperative that we not only address certain pressing problems but also identify several genuine system contradictions, which cannot be evaded and sooner or later must be resolved. Any credible agenda for renewal must be based on new paradigms of participation and models of governance, that will enable us to create patterns of decision-making far more suited to cope with emerging realities than the outmoded forms embedded in our current systems.Les problèmes financiers auxquels les universités sont présentement confrontées ne sont pas nouveaux comme une analyse rétrospective de la situation dans les années trente le démontrera. Cependant, "l'espace de décision" dans lequel chacun doit maintenant opérer est beaucoup plus circonscrit qu'il ne l'était dans le passé. Les contraintes provenant de l'externe augmentent continuellement en nombre et en intensité; la culture académique contemporaine a affaibli l'identité et les valeurs institutionnelles traditionnelles; et les structures de décision sont devenues excessivement complexes, lourdes et inadapteees aux réalités actuelles. Dans ces conditions, les demandes pressantes visant le renforcement des mécanismes de reddition de compte et le leadership ne peuvent être satisfaites. Il devient donc urgent de ne pas répondre seulement aux problèmes les plus pressants mais aussi d'identifier les contradictions systémiques qui tôt ou tard devront être confrontées et corrigées. Tout renouvellement, s'il veut être crédible, devra être axé sur de nouveaux modèles de participation et de gestion permettant de créer des modes nouveaux de décision mieux adaptés aux réalités modernes que les modèles traditionnels sur lesquels reposent toujours nos systèmes actuels