Slow inactivation in voltage-gated sodium channels

Slow inactivation in voltage-gated sodium channels is a biophysical process that governs the availability of sodium channels over extended periods of time. Slow inactivation, therefore, plays an important role in controlling membrane excitability, firing properties, and spike frequency adaptation. Defective slow inactivation is associated with several diseases of cell excitability, such as hyperkalemic periodic paralysis, myotonia, idiopathic ventricular fibrillation and long-QT syndrome. These associations underscore the physiological importance of this phenomenon. Nevertheless, our understanding of the molecular substrates for slow inactivation is still fragmentary. This review covers the current state of knowledge concerning the molecular underpinnings of slow inactivation, and its relationship with other biophysical processes of voltage-gated sodium channels.     

Structure of the core part of the lipopolysaccharides from Proteus penneri strains 7, 8, 14, 15, and 21

The core-lipid A region of the lipopolysaccharides from Proteus penneri strains 7, 8, 14, 15, and 21 was studied using NMR spectroscopy, ESI MS, and chemical analysis after alkaline deacylation, deamination, and mild-acid hydrolysis of the lipopolysaccharides. The following general structure of the major core oligosaccharides is proposed: [abstract: see text] where all sugars are in the pyranose form and have the D configuration unless otherwise stated, Hep and DDHep=L-glycero- and D-glycero-D-manno-heptose, respectively, K=H, and Q=H in strain 8 or alpha-Glc in strains 7, 14, 15, and 21. In addition, several minor structural variants are present, including those lacking Ara4N in strains 7 and 15 and having the alpha-GlcN residue N-acylated to a various degree with glycine in strains 7, 8, 14, and 21. In strain 14, there are also core oligosaccharides with K=amide of beta-D-GalpA with putrescine, spermidine, or 4-azaheptane-1,7-diamine; remarkably, these structural variants lack either the PEtN group or the alpha-Hep-(1-->2)-alpha-DDHep disaccharide fragment at alpha-D-GalpA. While structural features of the inner core part are shared by Proteus strains studied earlier, the outermost Q-(1-->4)-alpha-GalNAc-(1-->2)-alpha-DDHep-(1-->6)-alpha-GlcN oligosaccharide unit has not been hitherto reported.     

Structure of a new 2-deoxy-2-[(R)-3-hydroxybutyramido]-D-glucose-containing O-specific polysaccharide from the lipopolysaccharide of Citrobacter gillenii PCM 1542

The O-specific polysaccharide of Citrobacter gillenii PCM 1542 from serotype O-12a,12 b is composed of one residue each of D-glucose, D-GlcNAc, 2-deoxy-2-[(R)-3-hydroxybutyramido]-D-glucose (D-GlcNAcyl) and two GalNAc residues. On the basis of sugar and methylation analyses of the intact and Smith degraded polysaccharides, along with 1D and 2D 1H and 13C NMR spectroscopy, the following structure of the branched pentasaccharide repeating unit of the O-specific polysaccharide was established:This structure differs significantly from that of the O-specific polysaccharide of C. gillenii PCM 1544 from the same serotype O-12a,12 b, which has been established earlier (Kübler-Kielz.shtsls;b, J. et al. Carbohydr. Res. 2001, 331, 331-336). Serological studies confirmed that the two O-antigens are not related and suggested that strains PCM 1542 and 1544 should be classified into different O-serogroups.     

Structure of the O-polysaccharide of Aeromonas hydrophila O:34; a case of random O-acetylation of 6-deoxy-L-talose

The O-polysaccharide of Aeromonas hydrophila O:34 was obtained by mild-acid degradation of the lipopolysaccharide and studied by chemical methods and NMR spectroscopy before and after O-deacetylation. The polysaccharide was found to contain D-Man, D-GalNAc and 6-deoxy-L-talose (L-6dTal), and the following structure of the tetrasaccharide repeating unit was established [carbohydrate structure see text] where 6dTal(I) is O-acetylated stoichiometrically at position-2 and 6dTal(II) carries no, one or two O-acetyl groups at any positions.     

Superantigen-induced TCR alpha locus secondary rearrangement: role in tolerance induction

Immunization with superantigen in vivo induces transient activation of superantigen-specific T cells, followed by a superantigen-nonresponsive state. In this study, using a TCR alpha knock-in mouse in which the knock-in alpha-chain can be replaced with endogenous alpha-chain through secondary rearrangement, we show that immunization of superantigen changes the TCR alpha-chain expression on peripheral superantigen-specific T cells, induces expression of recombination-activating genes, and generates DNA double-strand breaks at the TCR alpha-chain locus. These results suggest that viral superantigens are capable of inducing peripheral TCR revision. Our findings thus provide a new perspective on pathogen-immune system interaction.     

Strand breaks produced in X-írradiated crystalline DNA: influence of base sequence

This study reports the radiation-chemical yields for DNA single-strand breaks (SSBs) in crystals of CGCACG:CGTGCG (I) and CACGCG:CGCGTG (II) duplexes induced by direct ionization using X rays. The DNA fragmentation products, consisting of 3'- and 5'-phosphate-terminated fragments, were quantified by ion-exchange chromatography using a set of reference compounds. The yields of single-strand breaks in I and II are 0.16 +/- 0.03 micro mol/J and 0.07 +/- 0.02 micro mol/J, respectively. The probability of cleavage at a given site is relatively independent of which of the four bases is at that site. For the very small sample of base sequences studied to date, there is no obvious dependence on base sequence. However, there appears to be an increased frequency of strand breaks at the non-phosphorylated termini of the oligodeoxynucleotides. These results show that direct ionization is efficient at producing single-strand breaks in DNA and that its action is relatively indiscriminate with respect to base sequence.     

The identity of the O-specific polysaccharide structure of Citrobacter strains from serogroups O2, O20 and O25 and immunochemical characterisation of C. youngae PCM 1507 (O2a,1b) and related strains

Serological studies using SDS-PAGE and immunoblotting revealed that from five strains that are ascribed to Citrobacter serogroup O2, four strains, PCM 1494, PCM 1495, PCM 1496 and PCM 1507, are reactive with specific anti-Citrobacter O2 serum. In contrast, strain PCM 1573 did not react with anti-Citrobacter O2 serum and, hence, does not belong to serogroup O2. The LPS of Citrobacter youngae O2a,1b (strain PCM 1507) was degraded under mild acidic conditions and the O-specific polysaccharide (OPS) released was isolated by gel chromatography. Sugar and methylation analyses along with (1)H- and (13)C-NMR spectroscopy, including two-dimensional (1)H,(1)H COSY, TOCSY, NOESY and (1)H,(13)C HSQC experiments, showed that the repeating unit of the OPS has the following structure: [structure: see text]. NMR spectroscopic studies demonstrated that Citrobacter werkmanii O20 and C. youngae O25 have the same OPS structure as C. youngae O2. Sugar and methylation analyses of the core oligosaccharide fractions demonstrated structural differences in the lipopolysaccharide core regions of these strains, which may substantiate their classification in different serogroups.     

The roles of annexins and types II and X collagen in matrix vesicle-mediated mineralization of growth plate cartilage

Annexins II, V, and VI are major components of matrix vesicles (MV), i.e. particles that have the critical role of initiating the mineralization process in skeletal tissues. Furthermore, types II and X collagen are associated with MV, and these interactions mediated by annexin V stimulate Ca(2+) uptake and mineralization of MV. However, the exact roles of annexin II, V, and VI and the interaction between annexin V and types II and X collagen in MV function and initiation of mineralization are not well understood. In this study, we demonstrate that annexin II, V, or VI mediate Ca(2+) influx into phosphatidylserine (PS)-enriched liposomes, liposomes containing lipids extracted from authentic MV, and intact authentic MV. The annexin Ca(2+) channel blocker, K-201, not only inhibited Ca(2+) influx into fura-2-loaded PS-enriched liposomes mediated by annexin II, V, or VI, but also inhibited Ca(2+) uptake by authentic MV. Types II and X collagen only bound to liposomes in the presence of annexin V but not in the presence of annexin II or VI. Binding of these collagens to annexin V stimulated its Ca(2+) channel activities, leading to an increased Ca(2+) influx into the liposomes. These findings indicate that the formation of annexin II, V, and VI Ca(2+) channels in MV together with stimulation of annexin V channel activity by collagen (types II and X) binding can explain how MV are able to rapidly take up Ca(2+) and initiate the formation of the first crystal phase.     

Milk Leptin Surge and Biological Rhythms of Leptin and Other Regulatory Proteins in Breastmilk

A significant number of chronic diseases are linked to perinatal nutrition, and prevention may be associated to naturally occurring components of breast milk. One key hormone in breast milk is leptin, related with the protection from obesity in the adulthood, thus knowing its changes through the day or lactation is crucial. We aimed to investigate the daily rhythms in the milk levels of leptin, together with other two related hormones, ghrelin and adiponectin, during lactation (days 5, 10 and 15) in rat dams, and the relation with morphometric parameters (dams and pups). Summarizing the main results, the existence of biological rhythms, but not daily and maybe circasemidian, was confirmed for the three hormones at the earliest period of lactation. The correlations performed generally showed a possible dependence of milk hormone levels on plasma levels at the early phase of lactation, while with the progression of lactation this dependence may fade and the hormone levels are suggested to be more dependent on mammary gland production/maturation. There was also a correlation between milk leptin and adiponectin levels, especially in the first half of lactation, suggesting a possible parallel regulation. Interestingly, we describe a milk leptin surge around the mid of lactation (at day 10) which may be related with pup´s growth (males and females) and with the well-known (in the literature) plasma leptin surge in pups. All this knowledge may be crucial for future applications in the development of formula milk and in relation with the role of leptin surge during lactation.     

Structures of mitochondrial oxidative phosphorylation supercomplexes and mechanisms for their stabilisation

Oxidative phosphorylation (OXPHOS) is the main source of energy in eukaryotic cells. This process is performed by means of electron flow between four enzymes, of which three are proton pumps, in the inner mitochondrial membrane. The energy accumulated in the proton gradient over the inner membrane is utilized for ATP synthesis by a fifth OXPHOS complex, ATP synthase. Four of the OXPHOS protein complexes associate into stable entities called respiratory supercomplexes. This review summarises the current view on the arrangement of the electron transport chain in mitochondrial cristae. The functional role of the supramolecular organisation of the OXPHOS system and the factors that stabilise such organisation are highlighted. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.