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.

Anomalous equilibrium binding properties of high-affinity racemic radioligands.

Abstract: In receptor binding studies, high-affinity racemic radioligands are often used as tracers, neglecting the difference in affinity of their stereoisomers. We present an experimental and theoretical study comparing the binding of (±)-[3H]carazolol and (±)-[125I]hydroxy-benzylpindolol (HYP) to their pure respective isomers in the frog erythrocyte beta-adrenergic system. Saturation binding curves with the racemic radioligands showed deviations from a binding isotherm for a single ligand which were accentuated at higher receptor concentrations. When different affinity constants for both isomers were considered, significant improvement in the fits of the data were obtained by computer-modeling procedures. The KDav (average dissociation constant) obtained by considering the racemic radioligand as a single ligand, as has generally been done in the literature, varied with the receptor concentration from approximately 2 KD(-) at low receptor concentrations to ≅0.5 KD(+) at high receptor concentrations. Thus the generally measured "KDav" of these racemic radioligands is really a hybrid of KD(-) and KD(+). These experimental findings are in very good agreement with Monte Carlo simulations and may help to explain the discrepancies in dissociation constants of high-affinity racemic radioligands reported in the literature. Experimental data and simulations also indicate that information about the KD(-) is greatest at low receptor concentrations, whereas that about KD(+) is greatest at high receptor concentrations. Simultaneous computer fitting of saturation curves from racemic [125I]HYP and the (+)-isomer, isolated by repeated incubations with frog erythrocyte membranes under appropriate conditions, indicates approximately a 20-fold ratio for the individual isomer KD values. Estimated KD values of the stereoisomers of [125I]HYP and [3H]carazolol were virtually identical, being KD(-) = 10-50 pM and KD(+) ≅ 400-2000 pM at 25°. Use of the KDav for a racemic radioligand resulted in up to 5-fold systematic underestimation of the affinity of nonracemic competitors. The KD values of all high-affinity competitors were also found to be misestimated by as much as 10-fold using the commonly employed Cheng and Prusoff [Biochem. Pharmacol.22: 3099-3108 (1973)] approximation when the affinity of the radioligand was significantly lower than that of the competitor. Under such circumstances, slope factors of ≅2 were obtained for competition curves in the absence of cooperativity.

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)