1,721,009 research outputs found
Targeting of proteins into and across the thylakoid membrane
No full textThe assembly of the photosynthetic apparatus utilizes component proteins that are synthesized by two genomes and then targeted into and across the thylakoid membrane. The emerging picture is one of a remarkably complex system of protein trafficking, in which at least four distinct pathways operate within the chloroplast - two for lumenal proteins and two for integral membrane proteins. Some of the pathways can be traced back to the prokaryotic ancestor of the chloroplast, whereas others appear to have arisen more recently - one in response to the transfer of genes to the plant nucleus and another, possibly, in response to the acquisition of new photosynthetic proteins. Remarkably, proteins in three of these pathways are synthesized with clearable signal-type peptides that are almost identical in overall structure, yet that execute entirely different functions. Recent studies have begun to reconcile the function of these targeting signals with the nature of the protein being targeted.</p
Determination of the unfrozen water content of maximally freeze-concentrated carbohydrate solutions
No full textThe heat capacity change at T′g has been studied in freeze-concentrated carbohydrate solutions. The values obtained have been compared with those found for high concentration solutions that do not undergo freezing above Tg. The analysis has indicated that the freezing process influences the degree of stress in the glassy phase. This results in a complex power-time curve when frozen solutions are heated in a differential scanning calorimeter. The endotherm produced by the stress relaxation can cause considerable error in W′g measurement obtained by any method that relies on the integration of the power-time curve. A more reliable method for W′g determination is via the intersection of T′g with a previously prepared Tg/Wg calibration curve.</p
Sec/SRP-independent insertion of two thylakoid membrane proteins bearing cleavable signal peptides
No full textAbstractTwo imported thylakoid membrane proteins, PSII-X and PSII-W, are synthesised with cleavable N-terminal signal peptides that closely resemble those of Sec-dependent lumenal proteins. In this report we have reconstituted the insertion of pre-PSII-X and pre-PSII-W into isolated thylakoids. We show that insertion does not require either nucleoside triphosphates or stromal extracts, both of which are required for Sec- and signal recognition particle (SRP)-dependent targeting mechanisms. Insertion is furthermore unaffected by protease treatments that destroy the known protein translocation apparatus in the thylakoid membrane. We conclude that these membrane proteins are inserted by an unusual Sec/SRP-independent mechanism that probably resembles that used by CFoII, and we discuss possible parallels with the biogenesis of phage M13 procoat
Acid sensitive background potassium channels K2p3.1 and K2p9.1 undergo rapid dynamin-dependent endocytosis
No full textAcid-sensitive, two-pore domain potassium channels, K2p3.1 and K2p9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K2p3.1 and K2p9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K2p3.1 and K2p9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K2p3.1 and K2p9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K2p3.1 and K2p9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K2p3.1 and K2p9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K2p3.1 and K2p9.1 trafficking can be further studied
Dual signal peptides mediate the signal recognition particle/Sec- independent insertion of a thylakoid membrane polyprotein, psbY
No full textThe nuclear psbY gene (formerly ycf32) encodes two distinct single- spanning chloroplast thylakoid membrane proteins in Arabidopsis thaliana. After import into the chloroplast, the precursor protein is processed to a polyprotein in which each 'mature' protein is preceded by an additional hydrophobic region; we show that these regions function as signal peptides that are cleaved after insertion into the thylakoid membrane. Inhibition of the first or second signal cleavage reaction by enlargement of the -1 residues leads in each case to the accumulation of a thylakoid-integrated intermediate containing three hydrophobic regions after import into chloroplasts; a double mutant is converted to a protein containing all four hydrophobic regions. We propose that the overall insertion process involves (i) insertion as a double-loop structure, (ii) two cleavages by the thylakoidal processing peptidase on the lumenal face of the membrane, and (iii) cleavage by an unknown peptidase on the stromal face on the membrane between the first mature protein and the second signal peptide. We also show that this polyprotein can insert into the thylakoid membrane in the absence of stromal factors, nucleoside triphosphates, or a functional Sec apparatus; this effectively shows for the first time that a multispanning protein can insert posttranslationally without the aid of signal recognition particle, SecA, or the membrane-bound Sec machinery.</p
An Arabidopsis cDNA encodes an apparent polyprotein of two non-identical thylakoid membrane proteins that are associated with photosystem II and homologous to algal ycf32 open reading frames
No full textAbstractWe have characterised an Arabidopsis thaliana cDNA homologous to the ycf32 open reading frames present in the Synechocystis genome and the plastid genomes of several eukaryotic algae. The predicted protein is also homologous to a novel protein reported to be associated with photosystem II. The protein is synthesised as a 23 kDa precursor with an N-terminal presequence that appears to be bipartite in structure, and the protein is targeted into the thylakoid membrane of pea chloroplasts. Although the Ycf32 presequence contains an apparent signal peptide, we find that this protein is not imported by either of the standard Sec- or ΔpH-dependent pathways. The mature protein is also unusual in two respects. First, there are two distinct, non-identical copies of typical single-span Ycf32 sequences in the Arabidopsis sequence, separated by an additional hydrophobic region. Secondly, the imported protein runs as a doublet of 6 kDa and 7 kDa polypeptides whereas the mature protein is predicted to be 14 kDa. We speculate that the protein undergoes further maturation once inserted into the thylakoid membrane to yield two separate Ycf32-like polypeptides
Life sciences in the central South: an economically strong region with a world-class natural environment and an innovative and collaborative life sciences sector
No full textThe Southern Policy Centre is an independent think tank and policy forum for central Southern England, founded in 2014. In promoting a regional public policy debate, the SPC has sought to make the case for a regional approach to economic and social policy. Based on the current strategies of local authorities and Local Economic Partnerships it has been possible to identify a strong and coherent region: the central South. Stretching from Portsmouth to Bournemouth Christchurch and Poole (BCP) and spanning the Isle of Wight and Hampshire, the central South can boast three coastal cities (Portsmouth, Southampton and BCP) with complementary economies, strong links to the rest of the UK, Europe and the world, strong universities, attractive culture, rich heritage and tourism. All are set within a superb natural environment with two national parks, areas of outstanding natural beauty and an ecologically rich coastline.Our first report on the central South was published in September 2019. Since then, the Southern Policy Centre has worked with local authorities, higher and further education, business and environmental organisations to set out the challenges and opportunities of the region. Details of our work on the future of our city centres, a GreenPrint for green recovery, and the central South’s case for ‘levelling-up’ can be found on our website.In this report, produced in collaboration with partners across the region , we examine the central South’s unsung stories: its strength in fostering and promoting the Life Sciences. We hope it will be useful to the region’s political and civic leaders in telling the story of the central South; to central government in understanding what the region has to offer the UK, and to those engaged in the regions life sciences in recognising the importance of what they do.AcknowledgementsSponsors of the report include: National Biofilms Innovation Centre, NIHR Clinical Research Network Wessex, University of Portsmouth, University Hospital Southampton NHS Foundation Trust, University of Southampton, Wessex Academic Health Science Network (Health Innovation Wessex). We are grateful to over 30 businesses, NHS Trusts, universities and other organisations across the south for contributing expertise to this report.Enquiries: The Southern Policy Centre closed in July 2023. For enquires about the report, please contact the Institute for Life Sciences by emailing [email protected]. <br/
Characterisation of an Arabidopsis thaliana cDNA encoding a novel thylakoid lumen protein imported by the ΔpH-dependent pathway
No full textAn Arabidopsis thaliana (L.) Heynh. cDNA encoding a novel 16-kDa protein (P16) of the chloroplast thylakoid lumen has been characterised. The function of the protein is unknown but it shares some sequence similarity with alpha allophycocyanins. P16 is synthesised with a bipartite, lumen-targeting presequence, and import experiments demonstrated that this protein follows the ΔpH-dependent pathway. Analysis of the thylakoid transfer peptide revealed two unusual features. Firstly, the key targeting determinant is predicted to be a twin-arginine followed by a highly hydrophobic residue two residues later, rather than at the third position as in most transfer peptides. Secondly, the C-terminal domain of the transfer peptide contains multiple charged residues which may help to prevent mistargeting by the Sec-type protein translocase.</p
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