Aldosterone: the mechanisms of molecular action

Aldosterone: a steroid hormone of adrenal cortex, has recently attracted much interest not only due to its great importance in regulation of salt and water balance, but also because of its key role in therapy of cardiovascular and renal pathology. The classical genomic mechanism of molecular action of aldosterone is mediated through interaction with mineral-corticoid receptors. Fast nongenomic pathway of cell signal transduction begins with interaction with hypothetic membrane receptors and includes activation of different kinase cascades. Interference of these two pathways of signal transduction assures abroad spectrum of aldosterone effects depending on the cell type, and also secures multycomponent regulation depending on the need of specific functional and stress situation. This review is dedicated to modern views of mechanisms of aldosterone molecular action, mostly of the level of aldosterone-sensitive segment of kidney nephron.     

Transport of ABA from the site of biosynthesis to the site of action

There is substantial evidence that abscisic acid (ABA) moves within plants. ABA has been considered as a root-derived signaling molecule that induces stomatal closure in response to dry soil conditions. It has been also reported that ABA synthesized in vegetative tissues is translocated to the seeds. The transport of ABA is an important factor in determining the endogenous concentrations of the hormone at the site of action, and hence, it is an important process in physiological responses. However, the molecular mechanisms that regulate ABA transport are not fully understood. Recent studies using Arabidopsis indicate that ABA is actively synthesized in leaf vascular tissues in response to drought, and that ABA is subsequently transported to the guard cells to close stomata. Identification of the transporters that mediate ABA export from the inside to the outside of the cells at the site of ABA biosynthesis (vascular tissues) and ABA uptake into the cells at the site of action (guard cells), respectively, in this species indicates an active mechanism to regulate ABA transport. Although Arabidopsis represents only one model plant, these findings are useful to discuss common or different regulatory mechanisms among different species and to improve our total understanding of the regulation of ABA transport.     

Aldosterone and the heart: from basic research to clinical evidence

Recent views suggest that long-term exposure to elevated aldosterone concentrations might result in cardiac, vascular, renal, and metabolic sequelae that occur independent of the blood pressure level. Indirect evidence of the untoward effects of aldosterone on the heart has been clearly established in clinical studies that have tested the effects of mineralocorticoid receptor antagonists in the treatment of systolic heart failure. As it has become clear in recent years, the interaction between aldosterone and the heart has to deal with additional actions of the hormone on specific cell types, cellular mechanisms, and molecules that are involved in regulation of tissue responses, leading to hypertrophy, remodeling, and fibrosis. The majority of these effects are mediated by activation of the mineralocorticoid receptors that are expressed in cardiomyocytes and cardiac fibroblasts, and mediate the genomic effects of the hormone. Evidence of interactions between aldosterone and the heart that occur independent of the renal effects of aldosterone, however, is not limited to the context of systolic heart failure and observations obtained in other disease states have led, together with findings of animal studies, to a better understanding of the potential benefits of aldosterone antagonists. In this narrative overview, we highlight the most recent findings that have been obtained in experimental animal models and in clinical conditions that include, in addition to systolic heart failure, primary aldosteronism, essential hypertension, diastolic heart failure, and arrhythmia.     

The mitochondrial proteome: from inventory to function

Mitochondria are central to cellular energetics, metabolism, and signaling. In this issue, Pagliarini et al. (2008) report the largest compendium of mammalian mitochondrial proteins to date. Together with proteomic studies in yeast, this study represents an important step toward the systematic characterization of the mitochondrial proteome and of mitochondrial diseases.     

Mining the fecal proteome: from biomarkers to personalised medicine

Introduction: Fecal proteomics has gained increased prominence in recent years. It can provide insights into the diagnosis and surveillance of many bowel diseases by both identifying potential biomarkers in stool samples and helping identify disease-related pathways. Fecal proteomics has already shown its potential for the discovery and validation of biomarkers for colorectal cancer screening, and the analysis of fecal microbiota by MALDI-MS for the diagnosis of a range of bowel diseases is gaining clinical acceptance.

Areas covered: Based on a comprehensive analysis of the current literature, we introduce the range of sensitive and specific proteomics methods which comprise the current ‘Proteomics Toolbox’, explain how the integration of fecal proteomics with data processing/bioinformatics has been used for the identification of potential biomarkers for both CRC and other gut-related pathologies and analysis of the fecal microbiome, outline some of the current fecal assays in current clinical practice and introduce the concept of personalised medicine which these technologies will help inform.

Expert commentary: Integration of fecal proteomics with other proteomics and genomics strategies as well as bioinformatics is paving the way towards personalised medicine, which will bring with it improved global healthcare.     

Arabidopsis thaliana proteomics: from proteome to genome

Proteomics has become an important approach for investigating cellular processes and network functions. Significant improvements have been made during the last few years in technologies for high-throughput proteomics, both at the level of data analysis software and mass spectrometry hardware. As proteomics technologies advance and become more widely accessible, efforts of cataloguing and quantifying full proteomes are underway to complement other genomics approaches, such as RNA and metabolite profiling. Of particular interest is the application of proteome data to improve genome annotation and to include information on post-translational protein modifications with the annotation of the corresponding gene. This type of analysis requires a paradigm shift because amino acid sequences must be assigned to peptides without relying on existing protein databases. In this review, advances and current limitations of full proteome analysis are briefly highlighted using the model plant Arabidopsis thaliana as an example. Strategies to identify peptides are also discussed on the basis of MS/MS data in a protein database-independent approach.     

Lipoarabinomannans: from structure to biosynthesis

Mycobacterium tuberculosis, the causative agent of tuberculosis, is one of the most effective human pathogens and the molecular basis of its virulence remains poorly understood. Here, we review our current knowledge about the structure and biosynthesis of the mycobacterial cell-wall lipoglycans, lipoarabinomannans (LAM). LAM are ubiquitous of mycobacteria and appear as the most potent non-peptidic molecules to modulate the host immune response. Nevertheless, LAM structure differs according to the mycobacterial species and three types of LAM have been described: mannose-capped LAM (ManLAM), phospho-myo-inositol-capped LAM (PILAM) and non-capped LAM (AraLAM). The type of capping is a major structural feature determining the ability of LAM to modulate the immune response. ManLAM, found in slow-growing mycobacteria, such as M. tuberculosis, have been demonstrated to be powerful anti-inflammatory molecules and emerge as key virulence factors that may be relevant drug targets. LAM-like molecules are not only confined to mycobacteria but are also present in actinomycetes (including the genera Rhodococcus, Corynebacterium or Gordonia). This offers the possibility of comparative studies that should help in deciphering the structure-function relationships and biosynthesis of these complex molecules in the future.     

Aldosterone as a factor of extracellular volume regulation: mechanism of action

The key role assumed by aldosterone in the regulation of extracellular volumes, requires that chloride moves along with sodium when active transport of the later ion is stimulated. In the mammalian nephron, aldosterone promotes reabsorption of sodium by the principal cells of the cortical portion of the collecting ducts. This results from hormone-induced increase in conductance for sodium at the apical pole of the target cells, and later on, from associated increased density of the sodium "pump" units at the basolateral pole. Studies carried out on amphibian epithelia indicate that chloride permeability - of mitochondria-rich cells, in all likelihood - is concurrently increased by aldosterone. It therefore looks as though this steroid hormone influences in a concerted way 2 cell populations, one being involved in transepithelial sodium transport, the other one representing the route of passage for the accompanying anion.     

Bacterial alginates: from biosynthesis to applications

Alginate is a polysaccharide belonging to the family of linear (unbranched), non-repeating copolymers, consisting of variable amounts of β-d-mannuronic acid and its C5-epimer α- l-guluronic acid linked via β-1,4-glycosidic bonds. Like DNA, alginate is a negatively charged polymer, imparting material properties ranging from viscous solutions to gel-like structures in the presence of divalent cations. Bacterial alginates are synthesized by only two bacterial genera, Pseudomonas and Azotobacter, and have been extensively studied over the last 40 years. While primarily synthesized in form of polymannuronic acid, alginate undergoes chemical modifications comprising acetylation and epimerization, which occurs during periplasmic transfer and before final export through the outer membrane. Alginate with its unique material properties and characteristics has been increasingly considered as biomaterial for medical applications. The genetic modification of alginate producing microorganisms could enable biotechnological production of new alginates with unique, tailor-made properties, suitable for medical and industrial applications.     

The genetic proteome: Using genetics to inform the proteome of mycobacterial pathogens

Mycobacterial pathogens pose a sustained threat to human health. There is a critical need for new diagnostics, therapeutics, and vaccines targeting both tuberculous and nontuberculous mycobacterial species. Understanding the basic mechanisms used by diverse mycobacterial species to cause disease will facilitate efforts to design new approaches toward detection, treatment, and prevention of mycobacterial disease. Molecular, genetic, and biochemical approaches have been widely employed to define fundamental aspects of mycobacterial physiology and virulence. The recent expansion of genetic tools in mycobacteria has further increased the accessibility of forward genetic approaches. Proteomics has also emerged as a powerful approach to further our understanding of diverse mycobacterial species. Detection of large numbers of proteins and their modifications from complex mixtures of mycobacterial proteins is now routine, with efforts of quantification of these datasets becoming more robust. In this review, we discuss the “genetic proteome,” how the power of genetics, molecular biology, and biochemistry informs and amplifies the quality of subsequent analytical approaches and maximizes the potential of hypothesis-driven mycobacterial research. Published proteomics datasets can be used for hypothesis generation and effective post hoc supplementation to experimental data. Overall, we highlight how the integration of proteomics, genetic, molecular, and biochemical approaches can be employed successfully to define fundamental aspects of mycobacterial pathobiology.     

Nuclear Envelope: Nanoarray Responsive to Aldosterone

Signalling between cytosol and nucleus is mediated by nuclear pores. These supramolecular complexes represent intelligent nanomachines regulated by a wide spectrum of factors. Among them, steroid hormones specifically interact with the pores and thus modify ion conductivity and macromolecule permeability of the nuclear envelope. In response to aldosterone the pores undergo dramatic changes in conformation, changes that depend on the nature of the transported cargo. Such changes can be imaged at the nanometer scale by using atomic force microscopy. Furthermore, steroid-induced macromolecule transport across the nuclear envelope causes osmotic water movements and nuclear swelling. Drugs that interact with intracellular steroid receptors (spironolactone) or with plasma membrane sodium channels (amiloride) inhibit swelling. Steroid hormone action is blocked when nuclear volume changes are prevented. This is shown in frog oocytes and human endothelial cells. In conclusion, nuclear pores serve as steroid-sensitive gates that determine nuclear activity.     

Aldosterone biosynthesis and cytochrome P-45011 beta: evidence for two different forms of the enzyme in rats

Whereas cytochrome P-45011 beta has been recently shown to catalyze the two-step conversion of corticosterone to aldosterone in the bovine and porcine adrenal cortex, the identity of the enzyme involved in the two final steps of aldosterone biosynthesis in the rat adrenal cortex is as yet unknown. Mitochondria from capsular adrenals of sodium-deficient, potassium-replete rats converted corticosterone to 18-hydroxycorticosterone and aldosterone at markedly higher rates than mitochondria from capsular adrenals of sodium-replete, potassium-deficient rats. However, the same preparations exhibited no difference in the 11 beta-hydroxylase activity, i.e. the conversion of deoxycorticosterone to corticosterone. Only mitochondria of zona glomerulosa from rats with stimulated aldosterone biosynthesis contained a 49K protein which showed a strong cross-reactivity with a monoclonal antibody raised against purified bovine cytochrome P-45011 beta. By contrast, a crossreactive protein with a molecular weight of 51K was found in mitochondria of zona fasciculata and in mitochondria of zona glomerulosa from rats with a suppressed aldosterone biosynthesis. These findings indicate the existence of two different forms of cytochrome P-45011 beta in the rat adrenal cortex, with only one of them, i.e. the 49K form, being capable of catalyzing the two final steps of aldosterone biosynthesis in situ.     

Antibiotic biosynthesis: from natural to unnatural compounds

The evolution of the field of biosynthesis from the unravelling of the mode of formation of natural products to the use of such knowledge to create new compounds is reviewed using examples from the author's laboratory. The discussion focuses on the mode of operation of type II (spore pigment PKS) and type I (rifamycin PKS) polyketide synthases and their diversion to generate unnatural products, and on the genetics and biochemistry of deoxysugar formation in granaticin biosynthesis as a prerequisite to combinatorial enzymatic synthesis of unusual glycosides. Journal of Industrial Microbiology & Biotechnology (2001) 27, 183–194. Received 21 September 1999/ Accepted in revised form 13 September 2000     

Lantibiotics: structure, biosynthesis and mode of action

The lantibiotics are a group of ribosomally synthesised, post-translationally modified peptides containing unusual amino acids, such as dehydrated and lanthionine residues. This group of bacteriocins has attracted much attention in recent years due to the success of the well characterised lantibiotic, nisin, as a food preservative. Numerous other lantibiotics have since been identified and can be divided into two groups on the basis of their structures, designated type-A and type-B. To date, many of these lantibiotics have undergone extensive characterisation resulting in an advanced understanding of them at both the structural and mechanistic level. This review outlines some of the more recent developments in the biochemistry, genetics and mechanism of action of these peptides.     

Neutrophil proteome: lessons from different standpoints

The present review brings a timeline of some of the major steps given throughout the years towards the development of our knowledge regarding the biology of the neutrophil. The contribution of early articles and their elementary biochemical approach is highlighted. The importance of the development of proteomic techniques is paralleled to the shift in neutrophil research towards high throughput molecular methods. As a last change of standpoint, the study of the neutrophil is presented integrated with other life- sciences technologies such as lipidomics, genomics and systems biology. The paper also brings a perspective/tendency overview at the same time that it discusses some of the difficulties encountered in the research of the neutrophil.