New insights into intracellular lipid binding proteins: The role of buried water

The crystal structures of most intracellular lipid binding proteins (LBPs) show between 5 and 20 internally bound water molecules, depending on the presence or the absence of ligand inside the protein cavity. The structural and functional significance of these waters has been discussed for several LBPs based on studies that used various biophysical techniques. The present work focuses on two very different LBPs, heart-type fatty acid binding protein (H-FABP) and ileal lipid binding protein (ILBP). Using high-resolution nuclear magnetic resonance spectroscopy, certain resonances belonging to side-chain protons that are located inside the water-filled lipid binding cavity were observed. In the case of H-FABP, the pH- and temperature-dependent behavior of selected side-chain resonances (Ser82 OgH and the imidazole ring protons of His93) indicated an unusually slow exchange with the solvent, implying that the intricate hydrogen-bonding network of amino-acid side-chains and water molecules in the protein interior is very rigid. In addition, holo H-FABP appeared to display a reversible self-aggregation at physiological pH. For ILBP, on the other hand, a more solvent-accessible protein cavity was deduced based on the pH titration behavior of its histidine residues. Comparison with data from other LBPs implies that the evolutionary specialization of LBPs for certain ligand types was not only because of mutations of residues directly involved in ligand binding but also to a refinement of the internal water scaffold.     

Clathrin-independent endocytosis: new insights into caveolae and non-caveolar lipid raft carriers

A number of recent studies have provided new insights into the complexity of the endocytic pathways originating at the plasma membrane of mammalian cells. Many of the molecules involved in clathrin coated pit internalization are now well understood but other pathways are less well defined. Caveolae appear to represent a low capacity but highly regulated pathway in a restricted set of tissues in vivo. A third pathway, which is both clathrin- and caveolae-independent, may constitute a specialized high capacity endocytic pathway for lipids and fluid. The relationship of this pathway, if any, to macropinocytosis or to the endocytic pathways of lower eukaryotes remains an interesting open question. Our understanding of the regulatory mechanisms and molecular components involved in this pathway are at a relatively primitive stage. In this review, we will consider some of the characteristics of different endocytic pathways in high and lower eukaryotes and consider some of the common themes in endocytosis. One theme which becomes apparent from comparison of these pathways is that apparently different pathways can share common molecular machinery and that pathways considered to be distinct actually represent similar basic pathways to which additional levels of regulatory complexity have been added.     

Oxysterol-Binding Protein: new insights into lipid transport functions and human diseases

Oxysterol-binding protein (OSBP) mediates lipid exchange between organelles at membrane contact sites, thereby regulating lipid dynamics and homeostasis. How OSBP's lipid transfer function impacts health and disease remain to be elucidated. In this review, we first summarize the structural characteristics and lipid transport functions of OSBP, and then focus on recent progresses linking OSBP with fatty liver disease, diabetes, lysosome-related diseases, cancer and viral infections, with the aim of discovering novel therapeutic strategies for common human diseases.     

Wolbachia genomes: insights into an intracellular lifestyle

The genome sequence of the Wolbachia endosymbiont that infects the nematode Brugia malayi has recently been determined together with three partial Wolbachia genomes from different Drosophila species. These data along with the previously published Wolbachia genome from Drosophila melanogaster provide new insights into how this endosymbiont has managed to become so successful.     

New insights into Chlamydia intracellular survival mechanisms

Chlamydia sp. are responsible for a wide range of diseases of significant clinical and public health importance. In this review, we highlight how recent cellular and functional genomic approaches have significantly increased our knowledge of the pathogenic mechanisms used by these genetically intractable bacteria. As the extensive repertoire of chlamydial proteins that are translocated into the mammalian host is identified and characterized, a molecular understanding of how Chlamydiae co-opt host cellular functions and block innate immune pathways is beginning to emerge.     

Turning receptors on and off with intracellular pepducins: new insights into G-protein-coupled receptor drug development

G-protein-coupled receptors (GPCRs) are a large family of remarkably versatile membrane proteins that are attractive therapeutic targets because of their involvement in a vast range of normal physiological processes and pathological diseases. Upon activation, intracellular domains of GPCRs mediate signaling to G-proteins, but these domains have yet to be effectively exploited as drug targets. Cell-penetrating lipidated peptides called pepducins target specific intracellular loops of GPCRs and have recently emerged as effective allosteric modulators of GPCR activity. The lipid moiety facilitates translocation across the plasma membrane, where pepducins then specifically modulate signaling of their cognate receptor. To date, pepducins and related lipopeptides have been shown to specifically modulate the activity of diverse GPCRs and other membrane proteins, including protease-activated receptors (PAR1, PAR2, and PAR4), chemokine receptors (CXCR1, CXCR2, and CXCR4), sphingosine 1-phosphate receptor-3 (S1P3), the melanocortin-4 receptor, the Smoothened receptor, formyl peptide receptor-2 (FPR2), the relaxin receptor (LGR7), G-proteins (Gα(q/11/o/13)), muscarinic acetylcholine receptor and vanilloid (TRPV1) channels, and the GPIIb integrin. This minireview describes recent advances made using pepducin technology in targeting diverse GPCRs and the use of pepducins in identifying potential novel drug targets.     

Phosphoproteomics: new insights into cellular signaling

Developments in the field of phosphoproteomics have been fueled by the need simultaneously to monitor many different phosphoproteins within the signaling networks that coordinate responses to changes in the cellular environment. This article presents a brief review of phosphoproteomics with an emphasis on the biological insights that have been derived so far.     

New insights into cardiovascular and lipid metabolomics

Metabolomics is the study of metabolite profiles in biological samples, particularly urine, saliva, blood plasma and fat biopsies. The metabolome is now considered by some to be the most predictive phenotype: consequently, the comprehensive and quantitative study of metabolites is a desirable tool for diagnosing disease, identifying new therapeutic targets and enabling appropriate treatments. A wealth of information about metabolites has been accumulated with global profiling tools and several candidate technologies for metabolomic studies are now available. Many high-throughput metabolomics methodologies are currently under development and have yet to be applied in clinical practice on a routine basis. In the cardiovascular field, few recent metabolomic studies have been reported so far. This minireview provides an updated overview of alternative technical approaches for metabolomics studies and reviews initial applications of metabolomics that relate to both cardiovascular disease and lipid metabolism research.     

Evolution of insect mushroom bodies: old clues,new insights

The mushroom bodies are a morphologically diverse sensory integration and learning and memory center in the brains of various invertebrate species, of which those of insects are the best described. Insect mushroom bodies are composed of numerous tiny intrinsic neurons (Kenyon cells) that form calyces with their dendrites and a pedunculus and lobes with their axons. The identities of conserved Kenyon cell subpopulations and the correlations between morphological and functional specializations of the mushroom bodies are just beginning to be elucidated, providing insight into mechanisms of mushroom body evolution. Comparisons of mushroom body organization in different insect lineages reveal trends in the evolution of subcompartments correlated with the elaboration, reduction, acquisition or loss of Kenyon cell subpopulations. Furthermore, these changes often appear correlated with variation in type and strength of afferent input and in behavioral ecology. These and other features of mushroom body organization suggest a striking convergence with mammalian cortex, with Kenyon cell subpopulations displaying evolutionary modularity in a manner reminiscent of cortical areas.     

A view into the blind spot: solution NMR provides new insights into signal transduction across the lipid bilayer

One of the most fundamental problems in cell biology concerns how cells communicate with their surroundings through surface receptors. The last few decades have seen major advances in understanding the mechanisms of receptor-ligand recognition and the biochemical consequences of such encounters. This review describes the emergence of solution nuclear magnetic resonance (NMR) spectroscopy as a powerful tool for the structural characterization of membrane-associated protein domains involved in transmembrane signaling. We highlight particularly instructive examples from the fields of immunoreceptor biology, growth hormone signaling, and cell adhesion. These signaling complexes comprise multiple subunits each spanning the membrane with a single helical segment that links extracellular ligand-binding domains to the cell interior. The apparent simplicity of this domain organization belies the complexity involved in cooperative assembly of functional structures that translate information across the cellular boundary.     

Storage diseases: new insights into sphingolipid functions

Studying human diseases can help us to uncover important processes in normal cells. Cell biologists have recently focused on inherited sphingolipid-storage diseases. Eukaryotic life is characterized by internal membranes of various compositions, and sphingolipids are a small but important part of these membranes. Compositional differences between cellular membranes are maintained by sorting and sphingolipids are thought to organize this process by forming ordered domains of increased thickness in the bilayer. Here, we describe the impact of sphingolipid accumulation on the sorting of endocytic membranes and discuss the proposed basis for the pathology of these diseases at the cellular level.     

Spliceosomal introns: new insights into their evolution

A new genome-wide analysis of spliceosomal introns indicates massive loss and gain of introns has taken place in many eukaryotic lineages. Only a small subset of the analyzed introns was present in the common ancestor of plants, fungi, animals and Plasmodium.     

Candida species: new insights into biofilm formation

Biofilms of Candida albicans, Candida parapsilosis, Candida glabrata and Candida tropicalis are associated with high indices of hospital morbidity and mortality. Major factors involved in the formation and growth of Candida biofilms are the chemical composition of the medical implant and the cell wall adhesins responsible for mediating Candida-Candida, Candida-human host cell and Candida-medical device adhesion. Strategies for elucidating the mechanisms that regulate the formation of Candida biofilms combine tools from biology, chemistry, nanoscience, material science and physics. This review proposes the use of new technologies, such as synchrotron radiation, to study the mechanisms of biofilm formation. In the future, this information is expected to facilitate the design of new materials and antifungal compounds that can eradicate nosocomial Candida infections due to biofilm formation on medical implants. This will reduce dissemination of candidiasis and hopefully improve the quality of life of patients.     

Deeper into the maize: new insights into genomic imprinting in plants

Current models for regulation of parent-specific gene expression in plants have been based on a small number of imprinted genes in Arabidopsis. These present repression as the default state, with expression requiring targeted activation. In general, repression is associated with maintenance methylation of cytosines, while no role has been found in Arabidopsis imprinting for de novo methylation--unlike the case in mammals. A recent paper both reinforces and challenges the model drawn from Arabidopsis. Methylation patterns of two imprinted loci in maize were tracked from gametes to offspring, enabling an exploration of the timing of imprinting. For one gene, fie1, the results were as expected: parent-specific methylation patterns were inherited from the three types of gamete: egg, central cell and sperm. The behaviour of fie2, however, was a surprise: no alleles were methylated in the gametes, although paternally contributed fie2 is methylated and silent in the endosperm, indicating that, in some cases, plant imprinting requires de novo DNA methylation. This work significantly broadens our understanding of plant imprinting and points to a greater diversity in imprinting mechanisms than has previously been appreciated.