An N-terminal diacidic motif is required for the trafficking of maize aquaporins ZmPIP2;4 and ZmPIP2;5 to the plasma membrane

Maize plasma membrane aquaporins (ZmPIPs, where PIP is the plasma membrane intrinsic protein) fall into two groups, ZmPIP1s and ZmPIP2s, which, when expressed alone in mesophyll protoplasts, are found in different subcellular locations. Whereas ZmPIP1s are retained in the endoplasmic reticulum (ER), ZmPIP2s are found in the plasma membrane (PM). We previously showed that, when co-expressed with ZmPIP2s, ZmPIP1s are relocalized to the PM, and that this relocalization results from the formation of hetero-oligomers between ZmPIP1s and ZmPIP2s. To determine the domains responsible for the ER retention and PM localization, respectively, of ZmPIP1s and ZmPIP2s, truncated and mutated ZmPIPs were generated, together with chimeric proteins created by swapping the N- or C-terminal regions of ZmPIP2s and ZmPIP1s. These mutated proteins were fused to the mYFP and/or mCFP, and the fusion proteins were expressed in maize mesophyll protoplasts, and were then localized by microscopy. This allowed us to identify a diacidic motif, DIE (Asp-Ile-Glu), at position 4–6 of the N-terminus of ZmPIP2;5, that is essential for ER export. This motif was conserved and functional in ZmPIP2;4, but was absent in ZmPIP2;1. In addition, we showed that the N-terminus of ZmPIP2;5 was not sufficient to cause the export of ZmPIP1;2 from the ER. A study of ZmPIP1;2 mutants suggested that the N- and C-termini of this protein are probably not involved in ER retention. Together, these results show that the trafficking of maize PM aquaporins is differentially regulated depending on the isoform, and involves a specific signal and mechanism.     

The High Throughput Sequence Annotation Service (HT-SAS) – the shortcut from sequence to true Medline words

Background  

Advances in high-throughput technologies available to modern biology have created an increasing flood of experimentally determined facts. Ordering, managing and describing these raw results is the first step which allows facts to become knowledge. Currently there are limited ways to automatically annotate such data, especially utilizing information deposited in published literature.     

Crystal Structure of a Yeast Aquaporin at 1.15 ? Reveals a Novel Gating Mechanism

Aquaporins are transmembrane proteins that facilitate the flow of water through cellular membranes. An unusual characteristic of yeast aquaporins is that they frequently contain an extended N terminus of unknown function. Here we present the X-ray structure of the yeast aquaporin Aqy1 from Pichia pastoris at 1.15 Å resolution. Our crystal structure reveals that the water channel is closed by the N terminus, which arranges as a tightly wound helical bundle, with Tyr31 forming H-bond interactions to a water molecule within the pore and thereby occluding the channel entrance. Nevertheless, functional assays show that Aqy1 has appreciable water transport activity that aids survival during rapid freezing of P. pastoris. These findings establish that Aqy1 is a gated water channel. Mutational studies in combination with molecular dynamics simulations imply that gating may be regulated by a combination of phosphorylation and mechanosensitivity.     

Origin and post-glacial dispersal of mitochondrial DNA haplogroups C and D in northern Asia

More than a half of the northern Asian pool of human mitochondrial DNA (mtDNA) is fragmented into a number of subclades of haplogroups C and D, two of the most frequent haplogroups throughout northern, eastern, central Asia and America. While there has been considerable recent progress in studying mitochondrial variation in eastern Asia and America at the complete genome resolution, little comparable data is available for regions such as southern Siberia--the area where most of northern Asian haplogroups, including C and D, likely diversified. This gap in our knowledge causes a serious barrier for progress in understanding the demographic pre-history of northern Eurasia in general. Here we describe the phylogeography of haplogroups C and D in the populations of northern and eastern Asia. We have analyzed 770 samples from haplogroups C and D (174 and 596, respectively) at high resolution, including 182 novel complete mtDNA sequences representing haplogroups C and D (83 and 99, respectively). The present-day variation of haplogroups C and D suggests that these mtDNA clades expanded before the Last Glacial Maximum (LGM), with their oldest lineages being present in the eastern Asia. Unlike in eastern Asia, most of the northern Asian variants of haplogroups C and D began the expansion after the LGM, thus pointing to post-glacial re-colonization of northern Asia. Our results show that both haplogroups were involved in migrations, from eastern Asia and southern Siberia to eastern and northeastern Europe, likely during the middle Holocene.     

Influence of sorbitol on protein production and glycosylation and cell wall formation in Trichoderma reesei

Sorbitol is often used at 1 mol/liter as an osmotic stabilizer for cultivation of fungi with a fragile cell wall phenotype. On the other hand, at this concentration sorbitol causes an osmotic stress in fungal cells resulting in intensive production of intracellular glycerol. The highly increased consumption of glucose for glycerol synthesis may lead to changes in processes requiring carbohydrate residues. This study provides new information on the consequences of osmotic stress to the cell wall composition, protein production and glycosylation, and cell morphology of Trichoderma reesei. We observed that high osmolarity conditions enhanced biomass production and strongly limited synthesis of cell wall glucans and chitin. Moreover, in these conditions the amount of secreted protein decreased nearly ten-fold and expression of cbh1 and cbh2 genes coding for cellobiohydrolase I and cellobiohydrolase II, the main secretory proteins in T. reesei, was inhibited resulting in a lack of the proteins in the cell and cultivation medium. The activity of DPM synthase, enzyme engaged in both N- and O-glycosylation pathways, was reduced two-fold, suggesting an overall inhibition of protein glycosylation. However, the two modes of glycosylation were affected divergently: O-glycosylation of secreted proteins decreased in the early stages of growth while N-glycosylation significantly increased in the stationary phase.     

The Peopling of Europe from the Mitochondrial Haplogroup U5 Perspective

It is generally accepted that the most ancient European mitochondrial haplogroup, U5, has evolved essentially in Europe. To resolve the phylogeny of this haplogroup, we completely sequenced 113 mitochondrial genomes (79 U5a and 34 U5b) of central and eastern Europeans (Czechs, Slovaks, Poles, Russians and Belorussians), and reconstructed a detailed phylogenetic tree, that incorporates previously published data. Molecular dating suggests that the coalescence time estimate for the U5 is ∼25–30 thousand years (ky), and ∼16–20 and ∼20–24 ky for its subhaplogroups U5a and U5b, respectively. Phylogeographic analysis reveals that expansions of U5 subclusters started earlier in central and southern Europe, than in eastern Europe. In addition, during the Last Glacial Maximum central Europe (probably, the Carpathian Basin) apparently represented the area of intermingling between human flows from refugial zones in the Balkans, the Mediterranean coastline and the Pyrenees. Age estimations amounting for many U5 subclusters in eastern Europeans to ∼15 ky ago and less are consistent with the view that during the Ice Age eastern Europe was an inhospitable place for modern humans.     

Arteriovenous oscillations of the redox potential: Is the redox state influencing blood flow?

Objective: Studies on the regulation of human blood flow revealed several modes of oscillations with frequencies ranging from 0.005 to 1 Hz. Several mechanisms were proposed that might influence these oscillations, such as the activity of vascular endothelium, the neurogenic activity of vessel wall, the intrinsic activity of vascular smooth muscle, respiration, and heartbeat. These studies relied typically on non-invasive techniques, for example, laser Doppler flowmetry. Oscillations of biochemical markers were rarely coupled to blood flow.

Methods: The redox potential difference between the artery and the vein was measured by platinum electrodes placed in the parallel homonymous femoral artery and the femoral vein of ventilated anesthetized pigs.

Results: Continuous measurement at 5 Hz sampling rate using a digital nanovoltmeter revealed fluctuating signals with three basic modes of oscillations: ～ 1, ～ 0.1 and ～ 0.01 Hz. These signals clearly overlap with reported modes of oscillations in blood flow, suggesting coupling of the redox potential and blood flow.

Discussion: The amplitude of the oscillations associated with heart action was significantly smaller than for the other two modes, despite the fact that heart action has the greatest influence on blood flow. This finding suggests that redox potential in blood might be not a derivative but either a mediator or an effector of the blood flow control system.     

Overgrowth of Douglas fir (Pseudotsuga menziesii Franco) stumps with regenerative tissue as an example of cell ordering and tissue reorganization

Main conclusion

Stump overgrowth may serve as a unique model for studying cellular reorganization and mechanisms responsible for cell polarity changes during the process of vascular tissue differentiation from initially unorganized parenchymatous cells. Cellular ordering and tissue reorganization during the overgrowth process of the transverse surfaces of Douglas fir stumps in forest stand was studied. At the beginning of stump overgrowth, the produced parenchymatous cells form an unorganized tissue. Particular parenchyma cells start arranging into more ordered structures which resemble rays. Application of digital image analysis software based on structure tensor was used. The analysis showed that at this stage of tissue development, cellular elements display a wide range of angular orientation values and attain very low coherency coefficients. The progress of the tissue differentiation process is associated with the formation of local regions with tracheids oriented circularly around the rays. This coincides with an increase in the range of angular orientations and greater values of coherency coefficients. At the most advanced stage of tissue development, with tracheids arranged parallelly in longitudinal strands, the degree of cell ordering is the highest what is manifested by the greatest values attained by coherency coefficients, and the narrow range of angular orientations. It is suggested that the ray-like structures could act as organizing centers in the morphogenetic field responsible for differentiation of the overgrowth tissue. The circular pattern of tracheids around rays in the initial phase of tissue development can be interpreted in terms of local rotation of the morphogenetic field which afterward is transformed into irrotational field. This transformation is noted by the presence of tracheids arranged parallelly in longitudinal strands. The possible involvement of a mechanism controlling cell polarity with respect to auxin transport is discussed.