| 1. |
- Alexandersson, Erik, et al.
(author)
-
Whole gene family expression and drought stress regulation of aquaporins
- 2005
-
In: Plant Molecular Biology. - : Springer Science and Business Media LLC. - 1573-5028 .- 0167-4412. ; 59:3, s. 469-484
-
Journal article (peer-reviewed)abstract
- Since many aquaporins (AQPs) act as water channels, they are thought to play an important role in plant water relations. It is therefore of interest to study the expression patterns of AQP isoforms in order to further elucidate their involvement in plant water transport. We have monitored the expression patterns of all 35 Arabidopsis AQPs in leaves, roots and flowers by cDNA microarrays, specially designed for AQPs, and by quantitative real-time reverse transcriptase PCR (Q-RT-PCR). This showed that many AQPs are pre-dominantly expressed in either root or flower organs, whereas no AQP isoform seem to be leaf specific. Looking at the AQP subfamilies, most plasma membrane intrinsic proteins (PIPs) and some tonoplast intrinsic proteins (TIPs) have a high level of expression, while NOD26-like proteins (NIPs) are present at a much lower level. In addition, we show that PIP transcripts are generally down-regulated upon gradual drought stress in leaves, with the exception of AtPIP1;4 and AtPIP2;5, which are up-regulated. AtPIP2;6 and AtSIP1;1 are constitutively expressed and not significantly affected by the drought stress. The transcriptional down-regulation of PIP genes upon drought stress could also be observed on the protein level.
|
|
| 2. |
- Berntorp, Kerstin, et al.
(author)
-
Initiation of biphasic insulin aspart 30/70 in subjects with type 2 diabetes mellitus in a largely primary care-based setting in Sweden.
- 2011
-
In: Primary Care Diabetes. - : Elsevier BV. - 1878-0210 .- 1751-9918. ; 5, s. 89-94
-
Journal article (peer-reviewed)abstract
- AIMS: Despite a wealth of clinical trial data supporting use of the premixed insulin analogue, biphasic insulin aspart 30 (BIAsp 30) in the treatment of type 2 diabetes mellitus (T2DM), there is limited documentation of its use in primary care-based clinical practice. METHODS: An observational study investigating the safety and efficacy of BIAsp 30 in routine clinical practice was conducted. Patients were followed up 3 and 6 months after initiating insulin treatment. Safety and efficacy measures were documented. RESULTS: During the course of the study, 1154 patients were included (age range 20-95years), of whom 89% completed the 6-month follow-up period. Mean HbA(1c) at baseline was 8.8% (73mmol/mol), and had improved to 7.2% (55mmol/mol) after 6 months of treatment. The rate of total hypoglycaemia at completion of the study was 4.1 events per patient year. Major hypoglycaemic events were rare (two in total). CONCLUSIONS: BIAsp 30 was initiated safely and effectively in insulin-naïve patients with T2DM. The safety and efficacy profile observed in clinical trials was confirmed in this largely primary care-based setting in Sweden.
|
|
| 3. |
- Johanson, Urban, et al.
(author)
-
The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for a new nomenclature for major intrinsic proteins in plants
- 2001
-
In: Plant Physiology. - : Oxford University Press (OUP). - 1532-2548 .- 0032-0889. ; 126:4, s. 1358-1369
-
Journal article (peer-reviewed)abstract
- Major intrinsic proteins (MIPs) facilitate the passive transport of small polar molecules across membranes. MIPs constitute a very old family of proteins and different forms have been found in all kinds of living organisms, including bacteria, fungi, animals, and plants. In the genomic sequence of Arabidopsis, we have identified 35 different MIP-encoding genes. Based on sequence similarity, these 35 proteins are divided into four different subfamilies: plasma membrane intrinsic proteins, tonoplast intrinsic proteins, NOD26-like intrinsic proteins also called NOD26-like MIPs, and the recently discovered small basic intrinsic proteins. In Arabidopsis, there are 13 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, nine NOD26-like intrinsic proteins, and three small basic intrinsic proteins. The gene structure in general is conserved within each subfamily, although there is a tendency to lose introns. Based on phylogenetic comparisons of maize (Zea mays) and Arabidopsis MIPs (AtMIPs), it is argued that the general intron patterns in the subfamilies were formed before the split of monocotyledons and dicotyledons. Although the gene structure is unique for each subfamily, there is a common pattern in how transmembrane helices are encoded on the exons in three of the subfamilies. The nomenclature for plant MIPs varies widely between different species but also between subfamilies in the same species. Based on the phylogeny of all AtMIPs, a new and more consistent nomenclature is proposed. The complete set of AtMIPs, together with the new nomenclature, will facilitate the isolation, classification, and labeling of plant MIPs from other species.
|
|
| 4. |
- Karlsson, Maria, 1985, et al.
(author)
-
Reconstitution of water channel function of an aquaporin overexpressed and purified from Pichia pastoris.
- 2003
-
In: FEBS Letters. - 1873-3468 .- 0014-5793. ; 537:1-3, s. 68-72
-
Journal article (peer-reviewed)abstract
- The aquaporin PM28A is one of the major integral proteins in spinach leaf plasma membranes. Phosphorylation/dephosphorylation of Ser274 at the C-terminus and of Ser115 in the first cytoplasmic loop has been shown to regulate the water channel activity of PM28A when expressed in Xenopus oocytes. To understand the mechanisms of the phosphorylation-mediated gating of the channel the structure of PM28A is required. In a first step we have used the methylotrophic yeast Pichia pastoris for expression of the pm28a gene. The expressed protein has a molecular mass of 32462 Da as determined by matrix-assisted laser desorption ionization-mass spectrometry, forms tetramers as revealed by electron microscopy and is functionally active when reconstituted in proteoliposomes. PM28A was efficiently solubilized from urea- and alkali-stripped Pichia membranes by octyl-beta-D-thioglucopyranoside resulting in a final yield of 25 mg of purified protein per liter of cell culture.
|
|
| 5. |
- Olsson, Ulf, et al.
(author)
-
In vivo and in vitro studies of Bacillus subtilis ferrochelatase mutants suggest substrate channeling in the heme biosynthesis pathway.
- 2002
-
In: Journal of Bacteriology. - 0021-9193. ; 184:14, s. 4018-4024
-
Journal article (peer-reviewed)abstract
- Ferrochelatase (EC 4.99.1.1) catalyzes the last reaction in the heme biosynthetic pathway. The enzyme was studied in the bacterium Bacillus subtilis, for which the ferrochelatase three-dimensional structure is known. Two conserved amino acid residues, S54 and Q63, were changed to alanine by site-directed mutagenesis in order to detect any function they might have. The effects of these changes were studied in vivo and in vitro. S54 and Q63 are both located at helix alpha3. The functional group of S54 points out from the enzyme, while Q63 is located in the interior of the structure. None of these residues interact with any other amino acid residues in the ferrochelatase and their function is not understood from the three-dimensional structure. The exchange S54A, but not Q63A, reduced the growth rate of B. subtilis and resulted in the accumulation of coproporphyrin III in the growth medium. This was in contrast to the in vitro activity measurements with the purified enzymes. The ferrochelatase with the exchange S54A was as active as wild-type ferrochelatase, whereas the exchange Q63A caused a 16-fold reduction in V(max). The function of Q63 remains unclear, but it is suggested that S54 is involved in substrate reception or delivery of the enzymatic product.
|
|
| 6. |
- Sjövall Larsen, Sara
(author)
-
Plant Aquaporins: A study of expression, localization, specificity, and regulation
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- Aquaporins, or Major Intrinsic Proteins (MIPs), are integral proteins that facilitate transport of water and other small neutral solutes across biological membranes. They belong to a well conserved and ancient family of proteins, present in all organisms ranging from bacteria to plants and humans. The aquaporin family in plants is large, indicating complex and regulated water transport within the plant in order to adapt to different environmental conditions. All aquaporin isoforms probably work together in an orchestrated manner, where each individual aquaporin isoform displays a specific localization pattern, substrate specificity, and regulatory mechanism. When analyzing the whole genome of the model plant Arabidopsis thaliana, 35 aquaporin-encoded genes were identified. Based on sequence similarities and by phylogenetic analyses they were divided into four subfamilies; Plasma membrane Intrinsic Proteins (PIPs), Tonoplast Intrinsic Proteins (TIPs), NOD26-like Intrinsic Proteins (NIPs), and Small basic Intrinsic Proteins (SIPs). These subfamilies are conserved in many plant species. Based on the four subfamilies a new uniform nomenclature for all plant aquaporins was proposed, which is now widely accepted and used. A gene expression study, using a DNA microarray and quantitative real-time reverse transcriptase PCR, of all the 35 aquaporin genes in Arabidopsis was performed. The relative amounts of each isoform in leaves, roots, and flowers were analyzed, as well as their individual responses to drought stress. Focusing on four of the nine isoforms in the Arabidopsis NIP subfamily, i.e. AtNIP1;2, AtNIP2;1, AtNIP4;2, and AtNIP6;1, the gene expression on tissue and cell level was studied with promoter::GUS constructs, the protein localization was studied on the subcellular level in different organs with immunoblots, and the permeability to water and glycerol was examined by heterologous expression in Xenopus oocytes. The spinach leaf plasma membrane aquaporin SoPIP2;1 was heterologously overexpressed in the yeast Pichia pastoris, purified, and functionally characterized by reconstitution into proteoliposomes. The water channel activity of SoPIP2;1 has previously been shown to be regulated by phosphorylation of Ser115 and Ser274. Two protein kinases, acting on these two phosphorylation sites in SoPIP2;1, were partly purified and characterized.
|
|
| 7. |
- Sjövall Larsen, Sara, et al.
(author)
-
Purification and characterization of two protein kinases acting on the aquaporin SoPIP2; 1
- 2006
-
In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736. ; 1758:8, s. 1157-1164
-
Journal article (peer-reviewed)abstract
- Aquaporins are water channel proteins that facilitate the movement of water and other small solutes across biological membranes. Plants usually have large aquaporin families, providing them with many ways to regulate the water transport. Some aquaporins are regulated post-translationally by phosphorylation. We have previously shown that the water channel activity of SoP1P2;1, an aquaporin in the plasma membrane of spinach leaves, was enhanced by phosphorylation at Ser115 and Ser274. These two serine residues are highly conserved in all plasma membrane aquaporins of the PIP2 subgroup. In this study we have purified and characterized two protein kinases phosphorylating Ser115 and Ser274 in SoPIP2;1. By anion exchange chromatography, the Ser115 kinase was purified from the soluble protein fraction isolated from spinach leaves. The Ca2+-dependent Ser274 kinase was purified by peptide affinity chromatography using plasma membranes isolated from spinach leaves. When characterized, the Ser115 kinase was Mg2+-dependent, Ca2+-independent and had a pH-optimum at 6.5. In accordance with previous studies using the oocyte expression system, site-directed mutagenesis and kinase and phosphatase inhibitors, the phosphorylation of Ser274, but not of Ser115, was increased in the presence of phosphatase inhibitors while kinase inhibitors decreased the phosphorylation of both Ser274 and Ser115. The molecular weight of the Ser274 kinase was approximately 50 kDa. The identification and characterization of these two protein kinases is an important step towards elucidating the signal transduction pathway for gating of the aquaporin SoPIP2;1.
|
|
