scholarly journals Starch metabolism in leaves.

2008 ◽  
Vol 55 (3) ◽  
pp. 435-445 ◽  
Author(s):  
Sławomir Orzechowski
Keyword(s):  
Translational Regulation ◽  
Higher Plants ◽  
Current Knowledge ◽  
Starch Synthesis ◽  
Starch Degradation ◽  
Starch Metabolism ◽  
Debranching Enzymes ◽  
Storage Carbohydrate ◽  
Branching Enzymes ◽  
Diphosphate Glucose

Starch is the most abundant storage carbohydrate produced in plants. The initiation of transitory starch synthesis and degradation in plastids depends mainly on diurnal cycle, post-translational regulation of enzyme activity and starch phosphorylation. For the proper structure of starch granule the activities of all starch synthase isoenzymes, branching enzymes and debranching enzymes are needed. The intensity of starch biosynthesis depends mainly on the activity of AGPase (adenosine 5'-diphosphate glucose pyrophosphorylase). The key enzymes in starch degradation are beta-amylase, isoamylase 3 and disproportionating enzyme. However, it should be underlined that there are some crucial differences in starch metabolism between heterotrophic and autotrophic tissues, e.g. is the ability to build multiprotein complexes responsible for biosynthesis and degradation of starch granules in chloroplasts. The observed huge progress in understanding of starch metabolism was possible mainly due to analyses of the complete Arabidopsis and rice genomes and of numerous mutants with altered starch metabolism in leaves. The aim of this paper is to review current knowledge on transient starch metabolism in higher plants.

scholarly journals Expression ofE. coliglycogen branching enzyme in anArabidopsismutant devoid of endogenous starch branching enzymes induces the synthesis of starch-like polyglucans

2015 ◽  
Author(s):  
Laura Boyer ◽  
Xavier Roussel ◽  
Adeline Courseaux ◽  
Ofilia Mvundza Ndjindji ◽  
Christine Lancelon-Pin ◽  
...  
Keyword(s):  
Double Mutant ◽  
Starch Synthesis ◽  
Water Soluble ◽  
Relative Importance ◽  
Branching Enzyme ◽  
Limited Impact ◽  
Debranching Enzymes ◽  
Branching Enzymes ◽  
Plant Storage ◽  
Glycogen Branching Enzyme

Starch synthesis requires several enzymatic activities including branching enzymes (BEs) responsible for the formation of α(1→6) linkages. Distribution and number of these linkages are further controlled by debranching enzymes (DBEs) that cleave some of them, rendering the polyglucan water-insoluble and semi-crystalline. Although the activity of BEs and DBEs is mandatory to sustain normal starch synthesis, the relative importance of each in the establishment of the plant storage polyglucan (i.e. water-insolubility, crystallinity, presence of amylose) is still debated. Here, we have substituted the activity of BEs inArabidopsiswith that of theEscherichia coliglycogen branching enzyme (GlgB). The latter is the BE counterpart in the metabolism of glycogen, a highly branched water-soluble and amorphous storage polyglucan. GlgB was expressed in thebe2 be3double mutant ofArabidopsisthat is devoid of BE activity and consequently free of starch. The synthesis of a water-insoluble, partly crystalline, amylose-containing starch-like polyglucan was restored in GlgB-expressing plants, suggesting that BEs origin only have a limited impact on establishing essential characteristics of starch. Moreover, the balance between branching and debranching is crucial for the synthesis of starch, as an excess of branching activity results in the formation of highly branched, water-soluble, poorly crystalline polyglucan.

scholarly journals Soluble Starch Synthase Enzymes in Cereals: An Updated Review

Agronomy ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1983
Author(s):  
Ahsan Irshad ◽  
Huijun Guo ◽  
Shoaib Ur Rehman ◽  
Xueqing Wang ◽  
Chaojie Wang ◽  
...  
Keyword(s):  
Structural Characteristics ◽  
Starch Synthesis ◽  
Soluble Starch ◽  
Starch Synthase ◽  
Cereal Crops ◽  
Starch Granules ◽  
Starch Structure ◽  
Debranching Enzymes ◽  
Branching Enzymes ◽  
Starch Yield

Cereal crops have starch in their endosperm, which has provided calories to humans and livestock since the dawn of civilization to the present day. Starch is one of the important biological factors which is contributing to the yield of cereal crops. Starch is synthesized by different enzymes, but starch structure and amount are mainly determined by the activities of starch synthase enzymes (SS) with the involvement of starch branching enzymes (SBEs) and debranching enzymes (DBEs). Six classes of SSs are found in Arabidopsis and are designated as soluble SSI-V, and non-soluble granule bound starch synthase (GBSS). Soluble SSs are important for starch yield considering their role in starch biosynthesis in cereal crops, and the activities of these enzymes determine the structure of starch and the physical properties of starch granules. One of the unique characteristics of starch structure is elongated glucan chains within amylopectin, which is by SSs through interactions with other starch biosynthetic enzymes (SBEs and DBEs). Additionally, soluble SSs also have conserved domains with phosphorylation sites that may be involved in regulating starch metabolism and formation of heteromeric SS complexes. This review presents an overview of soluble SSs in cereal crops and includes their functional and structural characteristics in relation to starch synthesis.

scholarly journals Regulation of ST6GAL1 sialyltransferase expression in cancer cells

Glycobiology ◽  
2020 ◽  
Author(s):  
Kaitlyn A Dorsett ◽  
Michael P Marciel ◽  
Jihye Hwang ◽  
Katherine E Ankenbauer ◽  
Nikita Bhalerao ◽  
...  
Keyword(s):  
Cancer Cells ◽  
Translational Regulation ◽  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Sialic Acids ◽  
Invasion Resistance ◽  
Cell Behaviors ◽  
Molecular Events ◽  
Wide Range

Abstract The ST6GAL1 sialyltransferase, which adds α2–6 linked sialic acids to N-glycosylated proteins, is overexpressed in a wide range of human malignancies. Recent studies have established the importance of ST6GAL1 in promoting tumor cell behaviors such as invasion, resistance to cell stress, and chemoresistance. Furthermore, ST6GAL1 activity has been implicated in imparting cancer stem cell characteristics. However, despite the burgeoning interest in the role of ST6GAL1 in the phenotypic features of tumor cells, insufficient attention has been paid to the molecular mechanisms responsible for ST6GAL1 upregulation during neoplastic transformation. Evidence suggests that these mechanisms are multifactorial, encompassing genetic, epigenetic, transcriptional, and post-translational regulation. The purpose of this review is to summarize current knowledge regarding the molecular events that drive enriched ST6GAL1 expression in cancer cells.

scholarly journals Novel Translation Initiation Regulation Mechanism in Escherichia coli ptrB Mediated by a 5′-Terminal AUG

2017 ◽  
Vol 199 (14) ◽  
Author(s):  
Heather J. Beck ◽  
Gary R. Janssen
Keyword(s):  
Escherichia Coli ◽  
Translation Initiation ◽  
Translational Regulation ◽  
Current Knowledge ◽  
Upstream Open Reading Frame ◽  
Model Organisms ◽  
Regulation Mechanism ◽  
Rna Regulation ◽  
Content Type ◽  
E Coli

ABSTRACT Alternative translation initiation mechanisms, distinct from the Shine-Dalgarno (SD) sequence-dependent mechanism, are more prevalent in bacteria than once anticipated. Translation of Escherichia coli ptrB instead requires an AUG triplet at the 5′ terminus of its mRNA. The 5′-terminal AUG (5′-uAUG) acts as a ribosomal recognition signal to attract ribosomes to the ptrB mRNA rather than functioning as an initiation codon to support translation of an upstream open reading frame. ptrB expression exhibits a stronger dependence on the 5′-uAUG than the predicted SD sequence; however, strengthening the predicted ptrB SD sequence relieves the necessity for the 5′-uAUG. Additional sequences within the ptrB 5′ untranslated region (5′-UTR) work cumulatively with the 5′-uAUG to control expression of the downstream ptrB coding sequence (CDS), thereby compensating for the weak SD sequence. Replacement of 5′-UTRs from other mRNAs with the ptrB 5′-UTR sequence showed a similar dependence on the 5′-uAUG for CDS expression, suggesting that the regulatory features contained within the ptrB 5′-UTR are sufficient to control the expression of other E. coli CDSs. Demonstration that the 5′-uAUG present on the ptrB leader mRNA is involved in ribosome binding and expression of the downstream ptrB CDS revealed a novel form of translational regulation. Due to the abundance of AUG triplets at the 5′ termini of E. coli mRNAs and the ability of ptrB 5′-UTR regulation to function independently of gene context, the regulatory effects of 5′-uAUGs on downstream CDSs may be widespread throughout the E. coli genome. IMPORTANCE As the field of synthetic biology continues to grow, a complete understanding of basic biological principles will be necessary. The increasing complexity of the synthetic systems highlights the gaps in our current knowledge of RNA regulation. This study demonstrates that there are novel ways to regulate canonical Shine-Dalgarno-led mRNAs in Escherichia coli, illustrating that our understanding of the fundamental processes of translation and RNA regulation is still incomplete. Even for E. coli, one of the most-studied model organisms, genes with translation initiation mechanisms that do not fit the canonical Shine-Dalgarno sequence paradigm are being revealed. Uncovering diverse mechanisms that control translational expression will allow synthetic biologists to finely tune protein production of desired gene products.

Functional diversity of the hnRNPs: past, present and perspectives

2010 ◽  
Vol 430 (3) ◽  
pp. 379-392 ◽  
Author(s):  
Siew Ping Han ◽  
Yue Hang Tang ◽  
Ross Smith
Keyword(s):  
Translational Regulation ◽  
Binding Proteins ◽  
Rna Binding ◽  
Rna Binding Proteins ◽  
Current Knowledge ◽  
Functional Divergence ◽  
Nucleic Acid Metabolism ◽  
Heterogeneous Nuclear Ribonucleoproteins ◽  
Nascent Transcripts

The hnRNPs (heterogeneous nuclear ribonucleoproteins) are RNA-binding proteins with important roles in multiple aspects of nucleic acid metabolism, including the packaging of nascent transcripts, alternative splicing and translational regulation. Although they share some general characteristics, they vary greatly in terms of their domain composition and functional properties. Although the traditional grouping of the hnRNPs as a collection of proteins provided a practical framework, which has guided much of the research on them, this approach is becoming increasingly incompatible with current knowledge about their structural and functional divergence. Hence, we review the current literature to examine hnRNP diversity, and discuss how this impacts upon approaches to the classification of RNA-binding proteins in general.

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