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41.
Jelena Cvetkovic Ilka Haferkamp Regina Rode Isabel Keller Benjamin Pommerrenig Oliver Trentmann Jacqueline Altensell Michaela Fischer-Stettler Simona Eicke Samuel C Zeeman H Ekkehard Neuhaus 《Plant physiology》2021,186(1):315
Maltose, the major product of starch breakdown in Arabidopsis (Arabidopsis thaliana) leaves, exits the chloroplast via the maltose exporter1 MEX1. Consequently, mex1 loss-of-function plants exhibit substantial maltose accumulation, a starch-excess phenotype and a specific chlorotic phenotype during leaf development. Here, we investigated whether the introduction of an alternative metabolic route could suppress the marked developmental defects typical for mex1 loss-of-function mutants. To this end, we ectopically expressed in mex1 chloroplasts a functional maltase (MAL) from baker’s yeast (Saccharomyces cerevisiae, chloroplastidial MAL [cpMAL] mutants). Remarkably, the stromal MAL activity substantially alleviates most phenotypic peculiarities typical for mex1 plants. However, the cpMAL lines contained only slightly less maltose than parental mex1 plants and their starch levels were, surprisingly, even higher. These findings point to a threshold level of maltose responsible for the marked developmental defects in mex1. While growth and flowering time were only slightly retarded, cpMAL lines exhibited a substantially improved frost tolerance, when compared to wild-types. In summary, these results demonstrate the possibility to bypass the MEX1 transporter, allow us to differentiate between possible starch-excess and maltose-excess responses, and demonstrate that stromal maltose accumulation prevents frost defects. The latter insight may be instrumental for the development of crop plants with improved frost tolerance.Expressing a yeast maltase in chloroplasts of the Arabidopsis maltose transporter mutant mex1 prevents the marked developmental defects typical for that mutant and enhances plant frost tolerance. 相似文献
42.
Maxime?J.?C. Audin Jan Philip Wurm Milos A. Cvetkovic Remco Sprangers 《Nucleic acids research》2016,44(6):2962-2973
The exosome plays an important role in RNA degradation and processing. In archaea, three Rrp41:Rrp42 heterodimers assemble into a barrel like structure that contains a narrow RNA entrance pore and a lumen that contains three active sites. Here, we demonstrate that this quaternary structure of the exosome is important for efficient RNA degradation. We find that the entrance pore of the barrel is required for nM substrate affinity. This strong interaction is crucial for processive substrate degradation and prevents premature release of the RNA from the enzyme. Using methyl TROSY NMR techniques, we establish that the 3′ end of the substrate remains highly flexible inside the lumen. As a result, the RNA jumps between the three active sites that all equally participate in substrate degradation. The RNA jumping rate is, however, much faster than the cleavage rate, indicating that not all active site:substrate encounters result in catalysis. Enzymatic turnover therefore benefits from the confinement of the active sites and substrate in the lumen, which ensures that the RNA is at all times bound to one of the active sites. The evolution of the exosome into a hexameric complex and the optimization of its catalytic efficiency were thus likely co-occurring events. 相似文献
43.
Noncontact dipole effects on channel permeation. III. Anomalous proton conductance effects in gramicidin 总被引:3,自引:2,他引:1 下载免费PDF全文
LR Phillips CD Cole RJ Hendershot M Cotten TA Cross DD Busath 《Biophysical journal》1999,77(5):2492-2501
Proton transport on water wires, of interest for many problems in membrane biology, is analyzed in side-chain analogs of gramicidin A channels. In symmetrical 0.1 N HCl solutions, fluorination of channel Trp(11), Trp-(13), or Trp(15) side chains is found to inhibit proton transport, and replacement of one or more Trps with Phe enhances proton transport, the opposite of the effects on K(+) transport in lecithin bilayers. The current-voltage relations are superlinear, indicating that some membrane field-dependent process is rate limiting. The interfacial dipole effects are usually assumed to affect the rate of cation translocation across the channel. For proton conductance, however, water reorientation after proton translocation is anticipated to be rate limiting. We propose that the findings reported here are most readily interpreted as the result of dipole-dipole interactions between channel waters and polar side chains or lipid headgroups. In particular, if reorientation of the water column begins with the water nearest the channel exit, this hypothesis explains the negative impact of fluorination and the positive impact of headgroup dipole on proton conductance. 相似文献
44.
The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus 总被引:1,自引:0,他引:1
Padgett RW; Loeb DD; Snyder LR; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1987,4(1):30-45
Recombinant DNA clones have been isolated that contain 80 kb of the
beta-globin complex from the deer mouse, Peromyscus maniculatus.
Comparisons of this complex with that from the laboratory mouse, Mus
domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3,
Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin
complex since the two species diverged. Unlike other mammals studied thus
far, the deer mouse possesses three adult genes. Partial sequence analysis
indicates that each of the three adult genes is intact and hence may be
functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to
genomic blots from Peromyscus reveals that it has a homologous counterpart
in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO
and Hbb-bhl, are also found in Peromyscus. The strong hybridization between
the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO
genes suggest that both pairs are important for the ontogeny of these mice
although no known product has been identified for the Hbb-bhO genes. The
presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication
that created this related gene set occurred before the two lineages
diverged. A single gene for Hbb-y has been isolated from Peromyscus. The
adult region in Peromyscus has undergone significant divergence from the
same region in Mus, having three rather than two adult genes, the
acquisition of at least 15 kb of extra DNA relative to Mus, and possibly
the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in
contrast, contains the same set of genes apparently distributed over the
same amount of DNA as in the Mus beta- globin complex. This observation
suggests that the embryonic region of the complex is more evolutionarily
stable than the adult region.
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