Robert J. Lefkowitz

Bio: Robert J. Lefkowitz is an academic researcher from Howard Hughes Medical Institute. The author has contributed to research in topics: Receptor & G protein-coupled receptor. The author has an hindex of 214, co-authored 860 publications receiving 147995 citations. Previous affiliations of Robert J. Lefkowitz include University of Nice Sophia Antipolis & University of Stuttgart.

GPCR signaling: conformational activation of arrestins.

Abstract: The arrestins, a small family of versatile adapter proteins, play central roles in G-protein coupled receptor (GPCR) desensitization, endocytosis, and signal transduction. Two papers by Latorraca et al. and Eichel et al. published recently in Nature, dissect the independent and concerted mechanisms by which the phosphorylated GPCR tail and transmembrane core conformationally enable arrestins to perform their diverse functions. G-protein coupled receptors (GPCRs), also known as seven transmembrane receptors (7 TMRs) are the largest family of cell surface proteins, with ~800 members identified in the human genome. They represent the commonest targets of therapeutic drugs used for the treatment of a wide range of health problems. Their remarkably diverse actions are mediated and modulated by the extracellular stimulus-driven interaction of the receptors with three families of proteins: the heterotrimeric guanine nucleotidebinding (G) proteins, the G protein-coupled receptor kinases (GRKs), and the arrestins. G proteins were discovered as the paradigmatic relay switches connecting the receptors to membrane effectors, such as second messenger-generating enzymes. GRKs and arrestins were discovered as a two-component system, which turns off the receptors. The activated receptors are phosphorylated by the kinases, typically on multiple sites on the cytoplasmic C-terminal tail. This leads to binding of the arrestins, initially to the phosphorylated receptor C tail, and then to the agonist-modified conformation of the 7 TM core. This occludes the G-protein-binding site on the receptor thus diminishing receptor G-protein signaling, a process known as receptor desensitization. There are four members of the arrestin family including two visual arrestins (arrestins 1 and 4), which are confined to the retina, and two universally expressed non-visual forms, arrestins 2 and 3, generally referred to as β-arrestin-1 and β-arrestin-2. Recently two papers have shed new light on the distinct roles of the phosphorylated receptor C-terminus and the 7 TM core in mediating arrestin interaction with and activation by GPCRs. Protein members of the versatile arrestin family contain two major domains (N and C), which consist largely of β-sheets and connecting loops. While initially discovered in the context of receptor desensitization, it was subsequently discovered that β-arrestins also serve as multifunctional adapters mediating receptor interaction with several components of the clathrincoated pit endocytic machinery, thus mediating receptor internalization and trafficking. They also bind to a long list of signaling proteins thus enabling β-arrestins to serve as signaling intermediates in their own right, acting either independently of or in concert with G-proteins to modulate cellular activities. The remarkable diversity of functions carried out by arrestins after their interaction with the receptors has engendered much interest in the mechanisms of GPCR-β-arrestin interactions and how these are translated into specific cellular consequences. Confirming decades-long ideas, recent structural studies of both visual arrestin interaction with rhodopsin and β-arrestin interaction with other GPCRs, have revealed two types of interactions within receptor-arrestin complexes: one involving the phosphorylated cytoplasmic tail of the GPCR (RP-tail), referred to as the ‘tail’ interaction, and one involving the transmembrane core of the GPCR, referred to as the ‘core’ interaction. It has been suggested that these are in turn mediated by two distinct sites on arrestins — a ‘phosphorylation sensor’ and an ‘activation sensor’. In the past, studies have largely focused on activation of arrestins by the RP-tail and its functional outcomes, 9 while the role of the receptor transmembrane core, if any, has remained obscure. However, the two new papers illuminate the distinct roles of both the RP-tail and the 7 TM core in mediating arrestin interaction with and activation by GPCRs. Specifically, these studies focus a much brighter light on the mechanisms of arrestin activation by the GPCR core. Using atomic-level molecular dynamic simulations of arrestin and β-arrestin, Latorraca and colleagues investigated the structural mechanisms by which the RP-tail, and the transmembrane core, in particular, regulate arrestin activation. In the simulations, the authors used a key conformational change in arrestin that occurs upon activation (a twist of the C domain of about 20° relative to the N domain) as a primary indicator of arrestin activation. According to current models, the initial step of arrestin activation requires the displacement of the long C tail of arrestin (which is folded back on the N domain in the inactive conformation) by the RP-tail of an activated GPCR. The authors show that this displacement of the arrestin C tail leads to prolongation in active state conformations of arrestin, even when not bound to the receptor. This may explain the previously noted curious finding that β-arrestin remains active and continues signaling following its dissociation from the activating GPCR. Using the rhodopsin-arrestin structure as a template for their simulations, the authors demonstrate that the receptor core and RP-tail each individually stabilize active conformations of arrestin (Fig. 1). The simultaneous binding of both regions as occurs with a full-length receptor adds further stabilization. According to their simulations, the key contacts responsible for the core interaction are between the receptor’s intracellular loops (ICLs), e.g., ICL-2 and ICL-3, and the C-loop and back loop in the C domain of arrestin, respectively. These computational findings are supported by fluorescence spectroscopic studies on arrestin mutants, which monitor conformational changes both at the RP-tail interface (the arrestin gate loop) and

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans

Abstract: Experimental introduction of RNA into cells can be used in certain biological systems to interfere with the function of an endogenous gene Such effects have been proposed to result from a simple antisense mechanism that depends on hybridization between the injected RNA and endogenous messenger RNA transcripts RNA interference has been used in the nematode Caenorhabditis elegans to manipulate gene expression Here we investigate the requirements for structure and delivery of the interfering RNA To our surprise, we found that double-stranded RNA was substantially more effective at producing interference than was either strand individually After injection into adult animals, purified single strands had at most a modest effect, whereas double-stranded mixtures caused potent and specific interference The effects of this interference were evident in both the injected animals and their progeny Only a few molecules of injected double-stranded RNA were required per affected cell, arguing against stochiometric interference with endogenous mRNA and suggesting that there could be a catalytic or amplification component in the interference process

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

Abstract: The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stressresponse or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole. (Endocrine Reviews 21: 55‐ 89, 2000)