EHBP1L1 coordinates Rab8 and Bin1 to regulate apical-directed transport in polarized epithelial cells

The highly conserved Rab guanosine triphosphatase (GTPase) Rab8 plays a role in exocytosis toward the polarized plasma membrane in eukaryotic cells. In murine Rab8-deficient small intestine cells, apical proteins are missorted into lysosomes. In this study, we identified a novel Rab8-interacting protein complex containing an EH domain–binding protein 1–like 1 (EHBP1L1), Bin1/amphiphysin II, and dynamin. Biochemical analyses showed that EHBP1L1 directly bound to GTP-loaded Rab8 and Bin1. The spatial dependency of these complexes at the endocytic recycling compartment (ERC) was demonstrated through overexpression and knockdown experiments. EHBP1L1- or Bin1-depleted or dynamin-inhibited small intestine organoids significantly accumulated apical membrane proteins but not basolateral membrane proteins in lysosomes. Furthermore, in EHBP1L1-deficient mice, small intestine cells displayed truncated and sparse microvilli, suggesting that EHBP1L1 maintains the apical plasma membrane by regulating apical transport. In summary, our data demonstrate that EHBP1L1 links Rab8 and the Bin1–dynamin complex, which generates membrane curvature and excises the vesicle at the ERC for apical transport.     

Crystal structure and substrate recognition mechanism of Aspergillus oryzae isoprimeverose-producing enzyme

Isoprimeverose-producing enzymes (IPases) release isoprimeverose (α-d-xylopyranosyl-(1?→?6)-d-glucopyranose) from the non-reducing end of xyloglucan oligosaccharides. Aspergillus oryzae IPase (IpeA) is classified as a member of the glycoside hydrolase family 3 (GH3); however, it has unusual substrate specificity compared with other GH3 enzymes. Xylopyranosyl branching at the non-reducing ends of xyloglucan oligosaccharides is vital for IpeA activity. We solved the crystal structure of IpeA with isoprimeverose at 2.4?Å resolution, showing that the structure of IpeA formed a dimer and was composed of three domains: an N-terminal (β/α)₈ TIM-barrel domain, α/β/α sandwich fold domain, and a C-terminal fibronectin-like domain. The catalytic TIM-barrel domain possessed a catalytic nucleophile (Asp300) and acid/base (Glu524) residues. Interestingly, we found that the cavity of the active site of IpeA was larger than that of other GH3 enzymes, and subsite ?1′ played an important role in its activity. The glucopyranosyl and xylopyranosyl residues of isoprimeverose were located at subsites ?1 and ?1′, respectively. Gln58 and Tyr89 contributed to the interaction with the xylopyranosyl residue of isoprimeverose through hydrogen bonding and stacking effects, respectively. Our findings provide new insights into the substrate recognition of GH3 enzymes.     

Expression of N-Acetylglucosaminyltransferase III Suppresses α2,3-Sialylation,and Its Distinctive Functions in Cell Migration Are Attributed to α2,6-Sialylation Levels

N-Acetylglucosaminyltransferase III (GnT-III), which catalyzes the addition of the bisecting GlcNAc branch on N-glycans, is usually described as a metastasis suppressor. Overexpression of GnT-III inhibited migration in multiple types of tumor cells. However, these results seem controversial to the clinical observations for the increased expression of GnT-III in human hepatomas, glioma, and ovarian cancers. Here, we present evidence that these inconsistencies are mainly attributed to the different expression pattern of cell sialylation. In detail, we show that overexpression of GnT-III significantly inhibits α2,3-sialylation but not α2,6-sialylation. The migratory ability of cells without or with a low level of α2,6-sialylation is consistently suppressed after GnT-III overexpression. In contrast, the effects of GnT-III overexpression are variable in tumor cells that are highly α2,6-sialylated. Overexpression of GnT-III promotes the cell migration in glioma cells U-251 and hepatoma cells HepG2, although it has little influence in human breast cancer cell MDA-MB-231 and gastric cancer cell MKN-45. Interestingly, up-regulation of α2,6-sialylation by overexpressing β-galactoside α2,6-sialyltranferase 1 in the α2,6-hyposialylated HeLa-S3 cells abolishes the anti-migratory effects of GnT-III. Conversely, depletion of α2,6-sialylation by knock-out of β-galactoside α2,6-sialyltranferase 1 in α2,6-hypersialylated HepG2 cells endows GnT-III with the anti-migratory ability. Taken together, our data clearly demonstrate that high expression of α2,6-sialylation on the cell surface could affect the anti-migratory role of GnT-III, which provides an insight into the mechanistic roles of GnT-III in tumor metastasis.     

Translational activation of ribosome-related genes at initial photoreception is dependent on signals derived from both the nucleus and the chloroplasts in Arabidopsis thaliana

Journal of Plant Research - Light is one of the indispensable elements that plants need in order to grow and develop. In particular, it is essential for inducing morphogenesis, such as suppression...     

Conformational preference of bicyclic β-amino acid dipeptides

Bridged bicyclic amino acids have high potential applicability as self-organized, conformationally constrained synthetic building blocks that do not require assistance from hydrogen bond formation. We systematically investigated the intrinsic conformational propensities of dipeptides of bridged bicyclic β-amino acids by means of accelerated molecular dynamics simulation and density functional theory (DFT) calculations in methanol, chloroform, and water. While the main-chain conformation, represented by φ and θ values, is fixed by the nature of the bicyclic ring structure, rotation of the C-terminal carbonyl group (ψ) is also restricted, converging to one or two minima. In endo-type dipeptides, in which the two N- and C-terminal amides are spatially close to each other, the C-terminal amide plane is placed horizontally. In exo-type dipeptides, in which the two amides are on opposite sides of the ring plane, the C-terminal carbonyl group can take two types of positions: either parallel/antiparallel with the N-terminal carbonyl or beneath the bicyclic ring, forcing the amide NHMe moiety to lie outside of the ring. We also examined the cis-trans preference of model bicyclic amides. Although the parent amides exhibit cis-trans equilibrium without any preference, addition of a methyl group on one of the bridgehead positions tips the equilibrium towards trans.     

Exaggerated evolution of male armaments via male–male competition

Males usually compete to gain access to prospective mates. Through this male–male competition, superior males have a higher chance of passing on their traits to the next generation of male offspring. One category of male traits is armaments, which are weapons used during competition, for example, the chelae of fiddler crabs and the antlers of deer. One consequence of intrasexual selection is the exaggerated evolution of armaments, which can be limited by trade‐offs, such as trade‐offs with male body size. Here, we formulate a game‐theoretic sexual selection model to explore the exaggerated evolution of armaments through male–male competition. The model is used to determine how competition affects the evolution of an armament that is subject to trade‐offs. Our simulation can be used to support the exaggerated evolution hypothesis, that is, male–male competition escalates the rate of evolution of armaments.     

Amino acid sequence of myoglobin from the chitonLiolophura japonica and a phylogenetic tree for molluscan globins

Myoglobin was isolated from the radular muscle of the chitonLiolophura japonica, a primitive archigastropodic mollusc.Liolophura contains three monomeric myoglobins (I, II, and III), and the complete amino acid sequence of myoglobin I has been determined. It is composed of 145 amino acid residues, and the molecular mass was calculated to be 16,070 D. The E7 distal histidine, which is replaced by valine or glutamine in several molluscan globins, is conserved inLiolophura myoglobin. The autoxidation rate at physiological conditions indicated thatLiolophura oxymyoglobin is fairly stable when compared with other molluscan myoglobins. The amino acid sequence ofLiolophura myoglobin shows low homology (11–21%) with molluscan dimeric myoglobins and hemoglobins, but shows higher homology (26–29%) with monomeric myoglobins from the gastropodic molluscsAplysia, Dolabella, andBursatella. A phylogenetic tree was constructed from 19 molluscan globin sequences. The tree separated them into two distinct clusters, a cluster for muscle myoglobins and a cluster for erythrocyte or gill hemoglobins. The myoglobin cluster is divided further into two subclusters, corresponding to monomeric and dimeric myoglobins, respectively.Liolophura myoglobin was placed on the branch of monomeric myoglobin lineage, showing that it diverged earlier from other monomeric myoglobins. The hemoglobin cluster is also divided into two subclusters. One cluster contains homodimeric, heterodimeric, tetrameric, and didomain chains of erythrocyte hemoglobins of the blood clamsAnadara, Scapharca, andBarbatia. Of special interest is the other subcluster. It consists of three hemoglobin chains derived from the bacterial symbiont-harboring clamsCalyptogena andLucina, in which hemoglobins are supposed to play an important role in maintaining the symbiosis with sulfide bacteria.