Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.4.1.18 (branching enzyme)
628 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

cDNA clones for two isoforms of starch branching enzyme (SBEI and SBEII) have been isolated from pea embryos and sequenced. The deduced amino acid sequences of pea SBEI and SBEII are closely related to starch branching enzymes of maize, rice, potato and cassava and a number of glycogen branching enzymes from yeast, mammals and several prokaryotic species. In comparison with SBEI, the deduced amino acid sequence of SBEII lacks a flexible domain at the N-terminus of the mature protein. This domain is also present in maize SBEII and rice SBEIII and resembles one previously reported for pea granule-bound starch synthase II (GBSSII). However, in each case it is missing from the other isoform of SBE from the same species. On the basis of this structural feature (which exists in some isoforms from both monocots and dicots) and other differences in sequence, SBEs from plants may be divided into two distinct enzyme families. There is strong evidence from our own and other work that the amylopectin products of the enzymes from these two families are qualitatively different. Pea SBEI and SBEII are differentially expressed during embryo development. SBEI is relatively highly expressed in young embryos whilst maximum expression of SBEII occurs in older embryos. The differential expression of isoforms which have distinct catalytic properties means that the contribution of each SBE isoform to starch biosynthesis changes during embryo development. Qualitative measurement of amylopectin from developing and maturing embryos confirms that the nature of amylopectin changes during pea embryo development and that this correlates with the differential expression of SBE isoforms.
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PMID:Starch branching enzymes belonging to distinct enzyme families are differentially expressed during pea embryo development. 789 9

Escherichia coli glycogen branching enzyme (GBE) and maize starch branching enzymes I (SBEI) and II (SBEII) were expressed in E. coli and purified. E. coli GBE branched amylose at a higher rate than did SBEII, but branched amylose at a lower rate than did SBEI. Similar to SBEI, GBE branched amylopectin at a lower rate than did SBEII. High-performance anion-exchange chromatography analysis of the branched products produced by BE revealed the minimum chain length (cl) required for branching. While GBE and SBEII showed the same minimum cl [degree of polymerization (dp) 12] required for branching, SBEI had a slightly higher minimum cl (dp 16) requirement for branching. The major differences between GBE and SBE are their specificities in terms of the size of chains transferred. In comparison with SBE, GBE had a much narrower size range of chains transferred and transferred mainly shorter chains. While SBEI and SBEII produced a large number of chains ranging from dp 6 to over dp 30, GBE predominantly transferred chains ranging from dp 5 to 16 and produced only a very small number of long chains with dp greater than 20. Although it has been reported that SBEI and SBEII preferentially transfer longer and shorter chains, respectively (1), this study further defines the differences between SBEI and SBEII in the size of chains transferred. SBEI predominantly transfers longer chains with dp greater than 10, while producing few shorter chains with dp 3 to 5. In contrast, SBEII preferentially transfers smaller chains with dp 3 to 9, with the most abundant chains being dp 6 and 7. The significance of minimum chain-length requirement by SBE is discussed in setting the invariant size of amylopectin cluster size (9 nm).
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PMID:Comparing the properties of Escherichia coli branching enzyme and maize branching enzyme. 918 17

Genomic DNA fragments from Triticum tauschii (D-genome donor to wheat) carrying starch branching enzyme I (SBE I) type genes have been characterized. One fragment contains one complete gene and two partial genes in 16 kb of DNA. One of the partial genes is oriented in the opposite strand to the other two. The gene that is complete was sequenced. Its structure corresponds closely to that of rice in that exons 3-8 are retained at similar sizes and spacings. A cDNA closely corresponding to the complete gene was isolated and characterized; it codes for a putative protein that represents a novel type of SBE I, as it is shorter at the 3' end than the forms reported so far in other plants. A second genomic fragment contains a different SBE I gene. There appear to be approximately 10 copies of SBE I type genes in wheat (approximately 5 in T. tauschii) and most of them have been assigned to group 7 chromosomes. In situ hybridization indicates that a major locus for the genes is located at the distal end of the short arm of chromosome 7D.
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PMID:A complex arrangement of genes at a starch branching enzyme I locus in the D-genome donor of wheat. 927 35

Full length cDNAs encoding a second starch branching enzyme (SBE A) isoform have been isolated from potato tubers. The predicted protein has a molecular mass of 101 kDa including a transit peptide of 48 amino acids. Multiple forms of the SBE A gene exist which differ mainly in the length of a polyglutamic acid repeat at the C-terminus of the protein. Expression of the mature protein in Escherichia coli demonstrates that the gene encodes an active SBE. Northern analysis demonstrates that SBE A mRNA is expressed at very low levels in tubers but is the predominant isoform in leaves. This expression pattern was confirmed by Western analysis using isoform specific polyclonal antibodies raised against E. coli expressed SBE A. SBE A protein is found predominantly in the soluble phase of tuber extracts, indicating a stromal location within the plastid. Transgenic potato plants expressing an antisense SBE A RNA were generated in which almost complete reductions in SBE A were observed. SBE activity in the leaves of these plants was severely reduced, but tuber activity was largely unaffected. Even so, the composition and structure of tuber starch from these plants was greatly altered. The proportion of linear chains was not significantly increased but the average chain length of amylopectin was greater, resulting in an increase in apparent amylose content as judged by iodine binding. In addition, the starch had much higher levels of phosphorous.
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PMID:A minor form of starch branching enzyme in potato (Solanum tuberosum L.) tubers has a major effect on starch structure: cloning and characterisation of multiple forms of SBE A. 1036 68

Analysis of DNA from Aegilops tauschii revealed that sequences hybridisable to the starch branching enzyme I (SBE I) gene were contained within a 53-kb fragment. There were at least four genes or gene fragments but of these only one appeared to encode the SBE I observed in the endosperm. Two large-insert DNA clones that encode SBE I from A. tauschii were isolated. Hybridisation analysis confirmed the presence of multiple SBE I gene type sequences within this DNA fragment of approximately 100 kb. Fluorescent in situ hybridisation (FISH) on extended DNA fibres provided further evidence of the close proximity of three of these genes. Sequence analysis was undertaken and this demonstrated that wSBE I-D3, wSBE I-D2 and wSBE I-D4 genes were clustered within 27 kb of DNA; of these only wSBE I-D4 encodes the SBE I purified from the endosperm. Multiple but distinct cDNAs containing SBE I-related sequences have been reported and these could arise from the SBE I locus by different transcription/splicing regimes.
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PMID:The starch branching enzyme I locus from Aegilops tauschii, the donor of the D genome to wheat. 1259 Mar 44

Studies of maize starch branching enzyme mutants suggest that the amylose extender high amylose starch phenotype is a consequence of the lack of expression of the predominant starch branching enzyme II isoform expressed in the endosperm, SBEIIb. However, in wheat, the ratio of SBEIIb and SBEIIa expression are inversely related to the expression levels observed in maize and rice. Analysis of RNA at 15 days post anthesis suggests that there are about 4-fold more RNA for SBE IIa than for SBE IIb. The genes for SBE IIa and SBE IIb from wheat are distinguished in the size of the first three exons, allowing isoform-specific antibodies to be produced. These antibodies were used to demonstrate that in the soluble fraction, the amount of SBE IIa protein is two to three fold higher than SBIIb, whereas in the starch granule, there is two to three fold more SBE IIb protein amount than SBE IIa. In a further difference to maize and rice, the genes for SBE IIa and SBE IIb are both located on the long arm of chromosome 2 in wheat, in a position not expected from rice-maize-wheat synteny.
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PMID:Starch branching enzyme IIb in wheat is expressed at low levels in the endosperm compared to other cereals and encoded at a non-syntenic locus. 1617 66

The transcriptional activity of the sorghum sbeIIb gene, encoding starch branching enzyme IIb, is seed specific, with expression in both the endosperm and the embryo. In comparison, expression of barley sbeIIb is confined to the endosperm, whereas that of barley sbeIIa occurs in endosperm, embryonic and vegetative tissues. It has been suggested that the second intron of barley sbeIIb may be instrumental in conferring endosperm-specific expression. Therefore, to further investigate the regulatory mechanisms of barley and sorghum sbe, we examined the tissue-specific activity of the sorghum sbe promoter in transient assays of green fluorescent protein (gfp) reporter constructs. We found that, when linked to the barley sbeIIb second intron, the sorghum sbeIIb promoter could not drive gfp transcription in sorghum or barley embryonic cells. Similar results were obtained for the barley sbeIIa promoter. Database searches showed that sequences homologous to the barley sbeIIb intron also exist in introns and flanking regions of some other grass genes. Deletion mutagenesis of the sorghum sbeIIb promoter identified the minimal promoters required for high- and low-level expression, respectively, but did not reveal any putative promoter elements crucial for expression. A sequence with similarity to the SURE element, implicated in sugar signaling, was located in the distal promoter region of sorghum sbeIIb, upstream of the minimal promoters. SURE elements are present in the proximal promoter regions of the sugar-regulated barley iso1 gene, and barley sbeIIb. In keeping in line with these observations, RNA-gel blot analyses demonstrated that expression of barley sbeIIb was sugar inducible, whereas that of sorghum sbeIIb was not.
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PMID:Transcriptional regulation of the sbeIIb genes in sorghum (Sorghum bicolor) and barley (Hordeum vulgare): importance of the barley sbeIIb second intron. 1661 88

The physicochemical properties of starch, such as apparent amylose content, gelatinization temperature, and pasting viscosities, determine the eating, cooking, and processing qualities of various products of rice. A recombinant inbred line (RIL) population derived from the reciprocal cross of Lemont (a premium high-quality tropical japonica rice) and Jiayu 293 (a high-yield but low-quality indica rice) was used to test the association of microsatellite markers of starch-synthesizing genes with starch quality parameters. The results confirmed the association of Wx and starch synthase I (SSI) alleles with various starch properties measured in rice flour. However, the starch properties were not associated with the starch branching enzyme 1 (SBE 1) gene alleles.
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PMID:Starch physicochemical properties and their associations with microsatellite alleles of starch-synthesizing genes in a rice RIL population. 1825 94

Full-length starch branching enzyme II (SBE, EC 2.4.1.18) cDNA from mungbean ( Vigna radiata L. cv. Tainan no. 5), VrsbeII, was cloned, characterized, and expressed as an active enzyme in Escherichia coli . Gene-specific primers first amplified an internal cDNA by reverse transcriptase Polymerase Chain Reaction (RT-PCR), followed by obtaining 5' and 3' fragments by RT-PCR and rapid amplification of cDNA ends (RACE). VrsbeII possesses a complete open reading frame (ORF) of 2571 bp, and the deduced polypeptide includes the common catalytic (beta/alpha)(8)-barrel domain and conserved regions of the alpha-amylase family. Phylogenetic analysis classified VrsbeII into SBE family A. Its partial 3D structure and functional features were predicted. VrsbeII has a shorter N-terminal among SBEs; however, two 6 bp (CCAGTT) direct repeat sequences (DRS) were found. A 24 bp shortened VrsbeII at the 3' end, skipping one DRS, was ligated into pET21b vector and expressed as His(6)-rVrSBEII in E. coli BL21 (DE3) cells. The optimal expression condition for rVrSBEII was evaluated and detected by Western blot with a molecular size of 108 kDa and activity of 6.4 U/mg.
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PMID:Cloning, characterization, and expression of mungbean ( Vigna radiata L.) starch branching enzyme II cDNA in Escherichia coli. 1914 23

The roles of starch branching enzyme (SBE, EC 2.4.1.18) IIa and SBE IIb in defining the structure of amylose and amylopectin in barley (Hordeum vulgare) endosperm were examined. Barley lines with low expression of SBE IIa or SBE IIb, and with the low expression of both isoforms were generated through RNA-mediated silencing technology. These lines enabled the study of the role of each of these isoforms in determining the amylose content, the distribution of chain lengths, and the frequency of branching in both amylose and amylopectin. In lines where both SBE IIa and SBE IIb expression were reduced by >80%, a high amylose phenotype (>70%) was observed, while a reduction in the expression of either of these isoforms alone had minor impact on amylose content. The structure and properties of the high amylose starch resulting from the concomitant reduction in the expression of both isoforms of SBE II in barley were found to approximate changes seen in amylose extender mutants of maize, which result from lesions eliminating expression of the SBE IIb gene. Amylopectin chain length distribution analysis indicated that both SBE IIa and SBE IIb isoforms play distinct roles in determining the fine structure of amylopectin. A significant reduction in the frequency of branches in amylopectin was noticed only when both SBE IIa and SBE IIb were reduced, whereas there was a significant increase in the branching frequency of amylose when SBE IIb alone was reduced. Functional interactions between SBE isoforms are suggested, and a possible inhibitory role of SBE IIb on other SBE isoforms is discussed.
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PMID:Control of starch branching in barley defined through differential RNAi suppression of starch branching enzyme IIa and IIb. 2015 42


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