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排序方式: 共有171条查询结果,搜索用时 15 毫秒
21.
22.
Delay of mating was examined as a possible mechanism for population decreases associated with mating disruption for codling moth, Cydia pomonella L., and obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). We examined the effect of delaying female mating 0, 2, 4, or 6 d while holding male age constant on life table parameters of both species. We found that increasing delays in mating were accompanied by two responses: (1) an increase in the percentage of sterile pairs and (2) a reduction in net reproductive rate and population growth unrelated to sterility. On a percentage basis, obliquebanded leafroller population growth was more strongly affected than codling moth. However, the net fertility rate of obliquebanded leafroller was nearly eight-fold higher than that of codling moth, so that obliquebanded leafroller females that experienced a 4-d delay in mating had nearly the same reproductive rate as codling moth females that experienced no delay. Leslie matrix simulations using life tables with field-based adult longevity estimates showed that codling moth females experiencing >2-d delay in mating resulted in decreases in population density or extinction within two generations. In contrast, obliquebanded leafroller females delayed <6 d showed rapid population growth that decreased as female age at mating increased; only the 6-d delay treatment resulted in decreased population levels. Our results indicate that obliquebanded leafroller females must on average experience a much longer delay in mating to significantly reduce population growth compared with codling moth females, suggesting that delay of mating likely plays a greater role in codling moth mating disruption than for obliquebanded leafroller. 相似文献
23.
In this protocol, we describe a procedure for incorporating ATP-binding cassette (ABC) transporters into large unilamellar vesicles (LUVs) and assays to determine ligand binding and solute translocation by these membrane-reconstituted systems. The reconstitution technique as described has been optimized for ABC transporters but can be readily adapted for other types of transport systems. Purified transporters are inserted into detergent-destabilized preformed liposomes and detergent is subsequently removed by adsorption onto polystyrene beads. Next, Mg-ATP or an ATP-regenerating system is incorporated into the vesicle lumen by one or more cycles of freezing-thawing, followed by extrusion through polycarbonate filters to obtain unilamellar vesicles. Binding and translocation of substrates are measured using isotope-labeled ligands and rapid filtration to separate the proteoliposomes from the surrounding medium. Quantitative information is obtained about dissociation constants (K(d)) for ligand binding, number of binding-sites, transport affinities (K(m)), rates of transport, and the activities of transporter molecules with opposite orientations in the membrane. The full protocol can be completed within 4-5 d. 相似文献
24.
Gecko phylogeography in the Western Indian Ocean region: the oldest clade of Ebenavia inunguis lives on the youngest island 下载免费PDF全文
25.
Fusarium fujikuroi associated with stem rot of red‐fleshed dragon fruit (Hylocereus polyrhizus) in Malaysia 下载免费PDF全文
M. Masratul Hawa I. Nurul Faziha M.N. Nik Mohamad Izham Z. Latiffah 《The Annals of applied biology》2017,170(3):434-446
Stem rot was recorded as one of serious diseases of red‐fleshed dragon fruit, (Hylocereus polyrhizus), in Malaysia. Fusarium fujikuroi was recovered from stem rot lesion of H. polyrhizus and the species was identified using TEF1‐α sequence and mating study. From maximum likelihood phylogenetic tree using combined TEF1‐α and β‐tubulin sequences, the F. fujikuroi isolates from stem rot were grouped according to three geographical locations, namely Peninsular Malaysia, Sabah and Sarawak. Phylogenetic analysis indicated that F. fujikuroi isolates from stem rot of H. polyrhizus were clustered separately from F. fujikuroi isolates from rice because of intraspecific variation. From amplification of MAT allele‐specific primers, 20% of the isolates carried MAT‐1 allele while 80% carried MAT‐2 allele. From isolates that carried MAT‐1 allele, 65% crossed‐fertile with MP‐C (mating population of F. fujikuroi) tester strain while for MAT‐2 allele, 56% crossed‐fertile with MP‐C. None of the isolates were identified as MP‐D (mating population of F. proliferatum). Pathogenicity test conducted on 40 representative isolates showed that the stem rot symptoms were similar with the symptoms observed in the field, and can be categorized as low, moderate and high aggressiveness, which indicated variation in pathogenicity and virulence among the isolates. This study provides novel findings regarding Fusarium species associated with stem rot of H. polyrhizus and indicated that F. fujikuroi as a new causal pathogen of the disease. 相似文献
26.
En route to economical eco‐friendly solvent system in enhancing sustainable recovery of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) copolymer 下载免费PDF全文
Nik Murniati Nik Man Irdahayu Kannusamy Shantini Kai‐Hee Huong Sevakumaran Vigneswari Nursolehah Abdul Aziz Mohd. Noor Mohd. Azizan Al‐Ashraf Abdullah Amirul 《Engineering in Life Science》2017,17(9):1050-1059
Separation of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐co‐4HB)] from bacterial cell matter is a critical step in the downstream process with respect to material quality and eco‐balance as P(3HB‐co‐4HB) is widely used for biomedical applications. Therefore, an efficient and eco‐based extraction of P(3HB‐co‐4HB) using a combination of NaOH and Lysol in digesting the non‐polymeric cell material (NPCM) digestion is developed. The NaOH and Lysol show synergistic influence on the copolymer extraction at a high purity and recovery of 97 and 98 wt% respectively. The optimized cell digestion method was found applicable to a vast batch of cells containing copolymers from various 4HB monomer compositions. At the largest extraction volume of 100 L, P(3HB‐co‐4HB) with a purity of 89 wt% was extracted with a maximum recovery of 90 wt%. The method developed has also eliminated the cell pretreatment step. The extraction method developed in this research has not only produced an economic and efficient copolymer recovery but has also retained the copolymer quality, in term of its molecular weight and thermal properties. It demonstrates a practical and promising downstream processing method in recovering the copolymer effectively from the bacterial biomass. 相似文献
27.
Nadiawati Alias Nor Muhammad Mahadi Abdul Munir Abdul Murad Farah Diba Abu Bakar Nik Azmi Nik Mahmood Rosli Md Illias 《World journal of microbiology & biotechnology》2009,25(4):561-572
A gene encoding endochitinase from Trichoderma virens UKM-1 was cloned and expressed in E. coli BL21 (DE3). Both the endochitinase gene and its cDNA sequences were obtained. The endochitinase gene encodes 430 amino acids
from an open reading frame comprising of 1,690 bp nucleotide sequence with three introns. The endochitinase was expressed
as soluble and active enzyme at 20°C when induced with 1 mM IPTG. Maximum activity was observed at 4 h of post-induction time.
SDS-PAGE showed that the purified endochitinase exhibited a single band with molecular weight of 42 kDa. Biochemical characterization
of the enzyme displayed a near neutral pH characteristic with an optimum pH at 6.0 and optimum temperature at 50°C. The enzyme
is stable between pH 3.0–7.0 and is able to retain its activity from 30 to 60°C. The presence of Mg2+ and Ca2+ ions increased the enzyme activity up to 20%. The purified enzyme has a strong affinity towards colloidal chitin and low
effect on ethyl cellulose and D-cellubiose which are non-chitin related substrates. HPLC analysis from the chitin hydrolysis
showed the release of (GlcNAc)3, (GlcNAc)2 and GlcNAc, in which (GlcNAc)2 was the main product. 相似文献
28.
Nik A. B. N. Mahmood Esther Biemans-Oldehinkel Bert Poolman 《The Journal of biological chemistry》2009,284(21):14368-14376
We have previously shown that the C-terminal cystathionine β-synthase
(CBS) domains of the nucleotide-binding domains of the ABC transporter OpuA,
in conjunction with an anionic membrane surface function, act as sensor of
internal ionic strength (Iin). Here, we show that a
surface-exposed cationic region in the CBS module domain is critical for ion
sensing. The consecutive substitution of up to five cationic residues led to a
gradual decrease of the ionic strength dependence of transport. In fact, a
5-fold mutant was essentially independent of salt in the range from 0 to 250
mm KCl (or NaCl), supplemented to medium of 30 mm
potassium phosphate. Importantly, the threshold temperature for transport was
lowered by 5–7 °C and the temperature coefficient
Q10 was lowered from 8 to ∼1.5 in the 5-fold mutant,
indicating that large conformational changes are accompanying the CBS-mediated
regulation of transport. Furthermore, by replacing the anionic C-terminal tail
residues that extend the CBS module with histidines, the transport of OpuA
became pH-dependent, presumably by additional charge interactions of the
histidine residues with the membrane. The pH dependence was not observed at
high ionic strength. Altogether the analyses of the CBS mutants support the
notion that the osmotic regulation of OpuA involves a simple biophysical
switching mechanism, in which nonspecific electrostatic interactions of a
protein module with the membrane are sufficient to lock the transporter in the
inactive state.In their natural habitats microorganisms are often exposed to changes in
the concentration of solutes in the environment
(1). A sudden increase in the
medium osmolality results in loss of water from the cell, loss of turgor, a
decrease in cell volume, and an increase in intracellular osmolyte
concentration. Osmoregulatory transporters such as OpuA in Lactococcus
lactis, ProP in Escherichia coli, and BetP in
Corynebacterium glutamicum diminish the consequences of the osmotic
stress by mediating the uptake of compatible solutes upon an increase in
extracellular osmolality
(2–4).
For the ATP-binding cassette
(ABC)5 transporter
OpuA, it has been shown that the system, reconstituted in proteoliposomes, is
activated by increased concentrations of lumenal ions (increased internal
ionic strength) (2,
5,
6). This activation is
instantaneous both in vivo and in vitro and only requires
threshold levels of ionic osmolytes. Moreover, the ionic threshold for
activation is highly dependent of the ionic lipid content (charge density) of
the membrane and requires the presence of so-called cystathionine
β-synthase (CBS) domains, suggesting that the ionic signal is transduced
to the transporter via critical interactions of the protein with membrane
lipids.The ABC transporter OpuA consists of two identical nucleotide-binding
domains (NBD) fused to CBS domains and two identical substrate-binding domains
fused to transmembrane domains. The NBD-CBS and substrate-binding
domain-transmembrane domain subunits are named OpuAA and OpuABC, respectively.
Two tandem CBS domains are linked to the C-terminal end of the NBD; each
domain (CBS1 and CBS2) has a β-α-β-β-α secondary
structure (5)
(Fig. 1A). The CBS
domains are widely distributed in most if not all species of life but their
function is largely unknown. Most of the CBS domains are found as tandem
repeats but data base searches have also revealed tetra-repeat units
(5). The crystal structures of
several tandem CBS domains have been elucidated
(7–9,
32), and in a number of cases
it has been shown that two tandem CBS domains form dimeric structures with a
total of four CBS domains per structural module (hereafter referred to as CBS
module). The crystal structures of the full-length MgtE Mg2+
transporter confirm the dimeric configuration and show that the CBS domains
undergo large conformational changes upon Mg2+ binding or release
(10,
11). In general, ABC
transporters are functional as dimers, which implies that two tandem CBS
domains are present in the OpuA complex. Preliminary experiments with
disulfides engineered at the interface of two tandem CBS domains in OpuA
suggest that large structural rearrangements (association-dissociation of the
interfaces) play a determining role in the ionic strength-regulated transport.
Finally, a subset of CBS-containing proteins has a C-terminal extension, which
in OpuA is highly anionic (sequence: ADIPDEDEVEEIEKEEENK) and modulates the
ion sensing activity (6).Open in a separate windowFIGURE 1.Domain structure of CBS module of OpuA. A, sequence of
tandem CBS domains. The predicted secondary structure is indicated
above the sequence. The residues modified in this study are
underlined. The amino acid sequence end-points of OpuAΔ61 and
OpuAΔ119 are indicated by vertical arrows. B, homology
model of tandem CBS domain of OpuA. The CBS domains were individually modeled
on the crystal structure of the tandem CBS protein Ta0289 from T.
acidophilum (PDB entry 1PVM), using Phyre. Ta0289 was used for the
initial modeling, because its primary sequence was more similar to the CBS
domains of OpuA than those of the other crystallized CBS proteins. The
individual domain models were then assembled with reference to the atomic
coordinates of the tandem CBS domains of IMPDH from Streptococcus
pyogenes (PDB entry 1ZFJ) to form the tandem CBS pair, using PyMOL
(DeLano). The positions of the (substituted) cationic residues are
indicated.In this study, we have engineered the surface-exposed cationic residues of
the CBS module and the C-terminal anionic tail of OpuA
(Fig. 1B). The ionic
strength and lipid dependence of the OpuA mutants were determined in
vivo and in vitro. We show that substitution of five cationic
residues for neutral amino acids is sufficient to inactivate the ionic
strength sensor and convert OpuA into a constitutively active transporter.
Moreover, by substituting six anionic plus four neutral residues of the
C-terminal anionic tail for histidines, the transport reaction becomes
strongly pH-dependent. 相似文献
29.
Mahmood NA Biemans-Oldehinkel E Patzlaff JS Schuurman-Wolters GK Poolman B 《The Journal of biological chemistry》2006,281(40):29830-29839
The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail. 相似文献
30.