Corelike structures in a stable L-form ofStreptococcus pyogenes

Corelike structures, which were interpreted as straight, large cylinders containing ribosome-like particles surrounded by an amorphous substance of low electron density, were found in a stable L-form ofStreptococcus pyogenes grown in the absence of antibiotics.     

Why does avian influenza A virus hemagglutinin bind to avian receptor stronger than to human receptor? Ab initio fragment molecular orbital studies

Influenza A viruses attach to alpha-sialosides on the target cell surface by their hemagglutinins, which strictly recognize the difference in sialic acid-galactose linkage. Why does avian virus H3 subtype bind to avian receptor Neu5Ac(alpha2-3)Gal stronger than to human receptor Neu5Ac(alpha2-6)Gal? Why does avian H3 mutated Gln226 to Leu preferentially bind to human receptor? In this paper, we theoretically answer the questions by molecular mechanics and ab initio fragment molecular orbital (FMO) calculations. The binding energy between avian H3 and avian receptor is 8.2kcal/mol larger than that of the avian H3-human receptor complex estimated at the FMO-HF/STO-3G level, which is a reason that avian H3 binds to avian receptor stronger than to human receptor. Avian Leu226 H3 clashes to Gal unit on the avian receptor to quite decrease its binding affinity. In contrast, Gal unit on the human receptor forms intermolecular hydrophobic interaction with avian Leu226 H3 to afford moderate binding affinity.     

Sequence Heterogeneity of the Ten rRNA Operons in Clostridium perfringens

We have cloned and sequenced rRNA operons of Clostridium perfringens strain 13 and analyzed the sequence structure in view of the phylogenesis. The organism had ten copies of rRNA operons all of that comprised of 16S, 23S and 5S rDNAs except for one operon. The operons clustered around the origin of replication, ranging within one-third of the whole genome sequence as it is arranged in a circle. Seven operons were transcribed in clockwise direction, and the remaining three were transcribed in counter clockwise direction assuming that the gyrA was transcribed in clockwise direction. Two of the counter clockwise operons contained tRNA^Ile genes between the 16S and 23S rDNAs, and the other had a tRNA^Ile genes between the 16S and 23S rDNAs and a tRNA^Asn gene in the place of the 5S rDNA. Microheterogeneity was found within the rRNA structural genes and spacer regions. The length of each 16S, 23S and 5S rDNA were almost identical among the ten operons, however, the intergenic spacer region of 16S-23S and 23S-5S were variable in the length depending on loci of the rRNA operons on the chromosome. Nucleotide sequences of the helix 19, helix 19a, helix 20 and helix 21 of 23S rDNA were divergent and the diversity appeared to be correlated with the loci of the rRNA operons on the chromosome.     

Unpaired structures in SCA10 (ATTCT)n.(AGAAT)n repeats

A number of human hereditary diseases have been associated with the instability of DNA repeats in the genome. Recently, spinocerebellar ataxia type 10 has been associated with expansion of the pentanucleotide repeat (ATTCT)(n).(AGAAT)(n) from a normal range of ten to 22 to as many as 4500 copies. The structural properties of this repeat cloned in circular plasmids were studied by a variety of methods. Two-dimensional gel electrophoresis and atomic force microscopy detected local DNA unpairing in supercoiled plasmids. Chemical probing analysis indicated that, at moderate superhelical densities, the (ATTCT)(n).(AGAAT)(n) repeat forms an unpaired region, which further extends into adjacent A+T-rich flanking sequences at higher superhelical densities. The superhelical energy required to initiate duplex unpairing is essentially length-independent from eight to 46 repeats. In plasmids containing five repeats, minimal unpairing of (ATTCT)(5).(AGAAT)(5) occurred while 2D gel analysis and chemical probing indicate greater unpairing in A+T-rich sequences in other regions of the plasmid. The observed experimental results are consistent with a statistical mechanical, computational analysis of these supercoiled plasmids. For plasmids containing 29 repeats, which is just above the normal human size range, flanked by an A+T-rich sequence, atomic force microscopy detected the formation of a locally condensed structure at high superhelical densities. However, even at high superhelical densities, DNA strands within the presumably compact A+T-rich region were accessible to small chemicals and oligonucleotide hybridization. Thus, DNA strands in this "collapsed structure" remain unpaired and accessible for interaction with other molecules. The unpaired DNA structure functioned as an aberrant replication origin, in that it supported complete plasmid replication in a HeLa cell extract. A model is proposed in which unscheduled or aberrant DNA replication is a critical step in the expansion mutation.     

Upregulation of uncoupling proteins by oral administration of capsiate, a nonpungent capsaicin analog.

Capsiate is a nonpungent capsaicin analog, a recently identified principle of the nonpungent red pepper cultivar CH-19 Sweet. In the present study, we report that 2-wk treatment of capsiate increased metabolic rate and promoted fat oxidation at rest, suggesting that capsiate may prevent obesity. To explain these effects, at least in part, we examined uncoupling proteins (UCPs) and thyroid hormones. UCPs and thyroid hormones play important roles in energy expenditure, the maintenance of body weight, and thermoregulation. Two-week treatment of capsiate increased the levels of UCP1 protein and mRNA in brown adipose tissue and UCP2 mRNA in white adipose tissue. This dose of capsiate did not change serum triiodothyronine or thyroxine levels. A single dose of capsiate temporarily raised both UCP1 mRNA in brown adipose tissue and UCP3 mRNA in skeletal muscle. These results suggest that UCP1 and UCP2 may contribute to the promotion of energy metabolism by capsiate, but that thyroid hormones do not.     

Off-response property of an acid-activated cation channel complex PKD1L3-PKD2L1

Ligand-gated ion channels are important in sensory and synaptic transduction. The PKD1L3-PKD2L1 channel complex is a sour taste receptor candidate that is activated by acids. Here, we report that the proton-activated PKD1L3-PKD2L1 ion channels have the unique ability to be activated after the removal of an acid stimulus. We refer to this property as the off-response (previously described as a delayed response). Electrophysiological analyses show that acid-induced responses are observed only after the removal of an acid solution at less than pH 3.0. A small increase in pH is sufficient for PKD1L3-PKD2L1 channel activation, after exposure to an acid at pH 2.5. These results indicate that this channel is a new type of ion channel-designated as an 'off-channel'-which is activated during stimulus application but not gated open until the removal of the stimulus. The off-response property of PKD1L3-PKD2L1 channels might explain the physiological phenomena occurring during sour taste sensation.     

Degenerative muscle fiber accelerates adipogenesis of intramuscular cells via RhoA signaling pathway

In some pathological conditions such as Duchenne muscular dystrophy, it has been known that a fatty infiltration in skeletal muscle is often observed and that is also one of primary factors to induce marked decline of muscular strength. However, the mechanism of fatty infiltration, cellular origin of accumulated adipocytes and its significance are not fully understood. The fact that persistent degenerative muscle fibers are present on dystrophic muscle leads us to hypothesize that muscle fiber condition affects fatty infiltration in skeletal muscle. We employed a single fiber culture system to determine whether fiber condition affects an appearance of adipocytes on the fibers. Artificially hyper-contracted muscle fibers (HCF), generated from isolated intact fibers (IF) of rat extensor digitrum longus muscle, were maintained as non-adherent cultures for 5–7 days. Interestingly, there appeared to be considerable numbers of mature adipocytes on HCF, whereas no adipocytes were seen on IF, indicating that cells on HCF spontaneously differentiated into mature adipocytes. Activation of RhoA signaling by the addition of thrombin decreased the number of adipocytes on HCF in a dose-dependent manner, whereas the number of MyoD-positive myoblasts increased. In contrast, Y-27632, a specific inhibitor of Rho kinases (ROCK), induced adipogenic differentiation of cells derived from IF. In addition, administration of Y-27632 into mouse regenerating muscle resulted in fat accumulation in the muscle. Taken together, the present studies clearly demonstrated that muscle fiber condition affects fat accumulation in skeletal muscle and that is possibly mediated by the RhoA signaling pathway.