| 1. |
- Brännström, Kristoffer, et al.
(författare)
-
Ca2+ enhances Aβ polymerization rate and fibrillar stability in a dynamic manner
- 2013
-
Ingår i: Biochemical Journal. - : Portland Press. - 0264-6021 .- 1470-8728. ; 450, s. 189-197
-
Tidskriftsartikel (refereegranskat)abstract
- Identifying factors that affect the self-assembly of the amyloid-β peptide (Aβ) is of utmost importance in the quest to understand the molecular mechanisms causing Alzheimer's disease (AD). Ca2+ has previously been shown to accelerate both Aβ fibril nucleation and maturation, and a dysregulated Ca2+ homeostasis frequently correlates with development of AD. The mechanisms regarding Ca2+ binding as well as its effect on fibril kinetics are not fully understood. Using a polymerization assay we show that Ca2+ in a dynamic and reversible manner enhances both the elongation rate and fibrillar stability, where specifically the "dock and lock" phase mechanism is enhanced. Through NMR analysis we found that Ca2+ affects the fibrillar architecture. In addition, and unexpectedly, we found that Ca2+ does not bind the free Aβ monomer. This implies that Ca2+ binding requires an architecture adopted by assembled peptides, and consequently is mediated through intermolecular interactions between adjacent peptides. This gives a mechanistic explanation to the enhancing effect on fibril maturation and indicates structural similarities between prefibrillar structures and mature amyloid. Taken together we expose how Ca2+ levels affect the delicate equilibrium between the monomeric and assembled Aβ and how fluctuations in vivo may contribute to development and progression of the disease.
|
|
| 2. |
- Frick, Anna, 1982, et al.
(författare)
-
Mercury increases water permeability of a plant aquaporin through a non-cysteine-related mechanism
- 2013
-
Ingår i: Biochemical Journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 454:pt 3, s. 491-499
-
Tidskriftsartikel (refereegranskat)abstract
- Water transport across cellular membranes is mediated by a family of membrane proteins known as AQPs (aquaporins). AQPs were first discovered on the basis of their ability to be inhibited by mercurial compounds, an experiment which has followed the AQP field ever since. Although mercury inhibition is most common, many AQPs are mercury insensitive. In plants, regulation of AQPs is important in order to cope with environmental changes. Plant plasma membrane AQPs are known to be gated by phosphorylation, pH and Ca2+. We have previously solved the structure of the spinach AQP SoPIP2;1 (Spinacia oleracea plasma membrane intrinsic protein 2; 1) in closed and open conformations and proposed a mechanism for how this gating can be achieved. To study the effect of mercury on SoPIP2; 1 we solved the structure of the SoPIP2;1-mercury complex and characterized the water transport ability using proteoliposomes. The structure revealed mercury binding to three out of four cysteine residues. In contrast to what is normally seen for AQPs, mercury increased the water transport rate of SoPIP2; 1, an effect which could not be attributed to any of the cysteine residues. This indicates that other factors might influence the effect of mercury on SoPIP2; 1, one of which could be the properties of the lipid bilayer.
|
|
| 3. |
- Sjögren, Jonathan, et al.
(författare)
-
EndoS2 is a unique and conserved enzyme of serotype M49 group A Streptococcus that hydrolyses N-linked glycans on IgG and α1-acid glycoprotein
- 2013
-
Ingår i: Biochemical Journal. - 0264-6021. ; 455:1, s. 107-118
-
Tidskriftsartikel (refereegranskat)abstract
- Many bacteria have evolved ways to interact with glycosylation functions of the immune system of their hosts. Streptococcus pyogenes [GAS (group A Streptococcus)] secretes the enzyme EndoS that cleaves glycans on human IgG and impairs the effector functions of the antibody. The ndoS gene, encoding EndoS, has, until now, been thought to be conserved throughout the serotypes. However, in the present study, we identify EndoS2, an endoglycosidase in serotype M49 GAS strains. We characterized EndoS2 and the corresponding ndoS2 gene using sequencing, bioinformatics, phylogenetic analysis, recombinant expression and LC–MS analysis of glycosidic activity. This revealed that EndoS2 is present exclusively, and highly conserved, in serotype M49 of GAS and is only 37% identical with EndoS. EndoS2 showed endo-β-N-acetylglucosaminidase activity on all N-linked glycans of IgG and on biantennary and sialylated glycans of AGP (α1-acid glycoprotein). The enzyme was found to act only on native IgG and AGP and to be specific for free biantennary glycans with or without terminal sialylation. GAS M49 expression of EndoS2 was monitored in relation to carbohydrates present in the culture medium and was linked to the presence of sucrose. We conclude that EndoS2 is a unique endoglycosidase in serotype M49 and differs from EndoS of other GAS strains by targeting both IgG and AGP. EndoS2 expands the repertoire of GAS effectors that modify key glycosylated molecules of host defence.
|
|
| 4. |
- Spégel, Peter, et al.
(författare)
-
Time-resolved metabolomics analysis of beta-cells implicates the pentose phosphate pathway in the control of insulin release
- 2013
-
Ingår i: Biochemical Journal. - 0264-6021. ; 450, s. 595-605
-
Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is coupled with changes in beta-cell metabolism. To define this process, 195 putative metabolites, mitochondrial respiration, NADP(+), NADPH and insulin secretion were measured within 15 mm of stimulation of clonal INS-1 832/13 beta-cells with glucose. Rapid responses in the major metabolic pathways of glucose occurred, involving several previously suggested metabolic coupling factors. The complexity of metabolite changes observed disagreed with the concept of one single metabolite controlling insulin secretion. The complex alterations in metabolite levels suggest that a coupling signal should reflect large parts of the beta-cell metabolic response. This was fulfilled by the NADPH/NADP(+) ratio, which was elevated (8-fold; P < 0.01) at 6 min after glucose stimulation. The NADPH/NADP+ ratio paralleled an increase in ribose 5-phosphate (>2.5-fold; P < 0.001). Inhibition of the pentose phosphate pathway by trans-dehydroepiandrosterone (DHEA) suppressed ribose 5-phosphate levels and production of reduced glutathione, as well as insulin secretion in INS-1 832/13 beta-cells and rat islets without affecting ATP production. Metabolite profiling of rat islets confirmed the glucose-induced rise in ribose 5-phosphate, which was prevented by DHEA. These findings implicate the pentose phosphate pathway, and support a role for NADPH and glutathione, in beta-cell stimulus-secretion coupling.
|
|
