Role of KIFC3 motor protein in Golgi positioning and integration

KIFC3, a microtubule (MT) minus end-directed kinesin superfamily protein, is expressed abundantly and is associated with the Golgi apparatus in adrenocortical cells. We report here that disruption of the kifC3 gene induced fragmentation of the Golgi apparatus when cholesterol was depleted. Analysis of the reassembly process of the Golgi apparatus revealed bidirectional movement of the Golgi fragments in both wild-type and kifC3-/- cells. However, we observed a markedly reduced inwardly directed motility of the Golgi fragments in cholesterol-depleted kifC3-/- cells compared with either cholesterol-depleted wild-type cells or cholesterol-replenished kifC3-/- cells. These results suggest that (a) under the cholesterol-depleted condition, reduced inwardly directed motility of the Golgi apparatus results in the observed Golgi scattering phenotype in kifC3-/- cells, and (b) cholesterol is necessary for the Golgi fragments to attain sufficient inwardly directed motility by MT minus end-directed motors other than KIFC3, such as dynein, in kifC3-/- cells. Furthermore, we showed that Golgi scattering was much more drastic in kifC3-/- cells than in wild-type cells to the exogenous dynamitin expression even in the presence of cholesterol. These results collectively demonstrate that KIFC3 plays a complementary role in Golgi positioning and integration with cytoplasmic dynein.     

Molecular cloning and characterization of novel ficolins from<Emphasis Type="Italic"> Xenopus laevis</Emphasis>

Ficolins are proteins characterized by the presence of collagen- and fibrinogen-like domains. Two of three human ficolins, L-ficolin and H-ficolin, are serum lectins and are thought to play crucial roles in host defense through opsonization and complement activation. To elucidate the evolution of ficolins and the primordial complement lectin pathway, we cloned four ficolin cDNAs from Xenopus laevis, termed Xenopus ficolin (XeFCN) 1, 2, 3 and 4. The deduced amino acid sequences of the four ficolins revealed the conserved collagen- and fibrinogen-like domains. The full sequences of the four ficolins showed a 42-56% identity to human ficolins, and 60-83% between one another. Northern blots showed that XeFCN1 was expressed mainly in liver, spleen and heart, and XeFCN2 and XeFCN4 mainly in peripheral blood leukocytes, lung and spleen. We isolated ficolin proteins from Xenopus serum by affinity chromatography on N-acetylglucosamine-agarose, followed by ion-exchange chromatography. The final eluate showed polymeric bands composed of two components of 37 and 40 kDa. The N-terminal amino acid sequences and treatment with endoglycosidase F showed that the two bands are the same XeFCN1 protein with different masses of N-linked sugar. The polymeric form of the two types of XeFCN1 specifically recognized GlcNAc and GalNAc residues. These results suggest that like human L-ficolin, XeFCN1 functions in the circulation through its lectin activity.     

Regulation by organic acids of polysaccharide-mediated microbe-plant interactions

A polysaccharide flocculant of Klebsiella pneumoniae H12 has been suggested to mediate microbe-plant interactions with the aid of Ca2+ [K. Nakata et al., Biosci. Biotechnol. Biochem., 64, 459-465, 2000]. Here, two-way regulation of polysaccharide-mediated interactions between K. pneumoniae and Raphanus sativus was studied using organic acids. Namely, 10 mM equivalents of organic acids promoted production of the polysaccharide by the bacterium, but inhibited flocculation of bacterial cells by the polysaccharide. These phenomena were counterbalanced by equi-molar equivalents of Ca2+, suggesting competition for Ca2+ between the carboxylic residues of the polysaccharide and those of the aliphatic acids. By electron microscopy observations, bacterial cell aggregates were sparsely distributed over the main roots and root hairs, had various sizes, and seemed to tightly adhere to root tissues. Their shapes seemed to be distorted and abundant in cavities. In brief, these microscopical observations may be explained by a two-way regulation system of bacterial adhesion to a plant by organic acids.     

Solution structures of the N-terminal domain of yeast calmodulin: Ca2+-dependent conformational change and its functional implication

We have determined solution structures of the N-terminal half domain (N-domain) of yeast calmodulin (YCM0-N, residues 1-77) in the apo and Ca(2+)-saturated forms by NMR spectroscopy. The Ca(2+)-binding sites of YCM0-N consist of a pair of helix-loop-helix motifs (EF-hands), in which the loops are linked by a short beta-sheet. The binding of two Ca(2+) causes large rearrangement of the four alpha-helices and exposes the hydrophobic surface as observed for vertebrate calmodulin (CaM). Within the observed overall conformational similarity in the peptide backbone, several significant conformational differences were observed between the two proteins, which originated from the 38% disagreement in amino acid sequences. The beta-sheet in apo YCM0-N is strongly twisted compared with that in the N-domain of CaM, while it turns to the normal more stable conformation on Ca(2+) binding. YCM0-N shows higher cooperativity in Ca(2+) binding than the N-domain of CaM, and the observed conformational change of the beta-sheet is a possible cause of the highly cooperative Ca(2+) binding. The hydrophobic surface on Ca(2+)-saturated YCM0-N appears less flexible due to the replacements of Met51, Met71, and Val55 in the hydrophobic surface of CaM with Leu51, Leu71, and Ile55, which is thought to be one of reasons for the poor activation of target enzymes by yeast CaM.     

Evaluation of nine sets of PCR primers in the RNA dependent RNA polymerase region for detection and differentiation of members of the family Caliciviridae, Norwalk virus and Sapporo virus

Norwalk virus and Sapporo virus were approved as type species of the genus "Norwalk-like viruses" and the genus "Sapporo-like viruses," respectively, in the family Caliciviridae. A total of 116 stool specimens containing Norwalk virus (NV) or Sapporo virus (SV) were tested by RT-PCR and Southern hybridization to evaluate nine sets of PCR primers and seven internal oligonucleotide probes in the RNA dependent RNA polymerase region of NV and SV for detection and differentiation of viruses in the NV and SV. Fifty-five stool samples were collected from 11 outbreaks of NV and/or SV gastroenteritis in an infant home, where residents were infants under 2 years of age, in Sapporo, Japan. Sixty specimens were obtained in Sapporo from sporadic cases in children, mainly under 6 years of age, of acute gastroenteritis due to small round structured viruses detected by EM. There is no single primer pair to detect all NV and SV, and at least three primer pairs, G1 set, G2 set and Sapp35/Sapp36, are required to detect viruses in the NV and SV clades. Many NV and SV strains were successfully classified into one of the NV/genogroup I, NV/genogroup II and SV by single-round RT-PCR and Southern hybridization. The new detection method for SV reported in this study combined with those for NV previously reported may elucidate the importance of Norwalk virus and Sapporo virus as a cause of viral gastroenteritis in all age groups in the world.     

Absolute configuration and tautomeric structure of xylindein, a blue-green pigment of Chlorociboria species

The S absolute configuration of both chiral centers of xylindein was assigned using X-ray crystallographic heavy atom analysis after its conversion to a synthetic derivative. Crystallographic analysis of xylindein crystallized with phenols revealed that the proposed structure is the proper tautomer in the crystals.     

Molecular cloning and expression of the mouse N-acetylneuraminic acid 9-phosphate synthase which does not have deaminoneuraminic acid (KDN) 9-phosphate synthase activity

A cDNA of the mouse homologue of Escherichia coli N-acetylneuraminic acid (Neu5Ac) synthase (neuB gene product) was cloned by the PCR-based method. The mouse homologue consists of 359 amino acids, and the cDNA sequence displays 33% identity to that of the E. coli Neu5Ac synthase. The recombinant mouse homologue which is transiently expressed in HeLa cells does not exhibit the Neu5Ac synthase activity, which catalyzes condensation of phosphoenolpyruvate (PEP) and N-acetylmannosamine (ManNAc) to synthesize Neu5Ac, but the Neu5Ac 9-phosphate (Neu5Ac-9-P) synthase activity, which catalyzes condensation of PEP and ManNAc 6-phosphate (ManNAc-6-P) to synthesize Neu5Ac-9-P. Thus, the mouse homologue of E. coli Neu5Ac synthase is the Neu5Ac-9-P synthase. The Neu5Ac-9-P synthase is a cytosolic enzyme and ubiquitously distributed in mouse various tissues. Notably, the Neu5Ac-9-P synthase can not catalyze the synthesis of deaminoneuraminic acid (KDN) or KDN-9-P from PEP and Man or ManNAc-6-P, thus suggesting that the enzyme is not involved in the synthesis of KDN. This is consistent with the previous observation that only a very low activity to synthesize KDN is found in mouse B16 cells [Angata, T., et al. (1999) Biochem. Biophys. Res. Commun. 261, 326-331].