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1.
Structural localization of the sequence alpha 235-242 of the nicotinic acetylcholine receptor 总被引:1,自引:0,他引:1
M Criado V Sarin J L Fox J Lindstrom 《Biochemical and biophysical research communications》1985,128(2):864-871
Two monoclonal antibodies (mAb 254 and 255) were obtained against a synthetic peptide corresponding to the sequence 235-242 of the alpha-subunit of Torpedo acetylcholine receptor. These mAbs could bind to receptor in native membrane vesicles only when these vesicles were permeabilized, suggesting that the sequence alpha 235-242 is exposed on the cytoplasmic surface of the receptor. Further evidence for the cytoplasmic localization of this sequence was partial competition for binding between these mAbs and mAbs previously demonstrated to bind to the cytoplasmic part of the receptor. A model is proposed which accounts for all the experimental data obtained thus far on the transmembrane orientation of the subunit polypeptide chains. 相似文献
2.
J W Wray W A Baase J D Lindstrom L H Weaver A R Poteete B W Matthews 《Journal of molecular biology》1999,292(5):1111-1120
The mutation Glu108-->Val (E108V) in T4 lysozyme was previously isolated as a second-site revertant that specifically compensated for the loss of function associated with the destabilizing substitution Leu99-->Gly (L99G). Surprisingly, the two sites are 11 A apart, with Leu99 in the core and Glu108 on the surface of the protein. In order to better understand this result we have carried out a detailed thermodynamic, enzymatic and structural analysis of these mutant lysozymes as well as a related variant with the substitution Leu99-->Ala. It was found that E108V does increase the stability of L99G, but it also increases the stability of both the wild-type protein and L99A by essentially equal amounts. The effects of E108V on enzymatic activity are more complicated. The mutation slightly reduces the maximal rate of cell wall hydrolysis of wild-type, L99G and L99A. At the same time, L99G is an unstable protein and rapidly loses activity during the course of the assay, especially at temperatures above 20 degrees C. Thus, even though the double mutant L99G/E108V has a slightly lower maximal rate than L99G, over a period of 20-30 minutes it hydrolyzes more substrate. This decrease in the rate of thermal inactivation appears to be the basis of the action of E108V as a second-site revertant of L99G. Mutant L99A creates a cavity of volume 149 A(3). Instead of enlarging this cavity, mutant L99G results in a 4-5 A displacement of part of helix F (residues 108-113), creating a solvent-accessible declivity. In the double mutant, L99G/E108V, this helix returns to a position akin to wild-type, resulting in a cavity of volume 203 A(3). Whether the mutation Glu108-->Val is incorporated into either wild-type lysozyme, or L99A or L99G, it results in a decrease in crystallographic thermal factors, especially in the helices that include residues 99 and 108. This increase in rigidity, which appears to be due to a combination of increased hydrophobic stabilization plus a restriction of conformational fluctuation, provides a structural basis for the increase in thermostability. 相似文献
3.
A. G. Carnon A. Ssemwogerere D. W. Lamont D. J. Hole E. A. Mallon W. D. George G. R. Gillis 《BMJ (Clinical research ed.)》1994,309(6961):1054-1057
OBJECTIVE--To investigate the relation between socioeconomic deprivation and pathological prognostic factors in women with breast cancer as a possible explanation for socioeconomic differences in survival. DESIGN--Retrospective analysis of data from cancer registry and from pathology and biochemistry records. SETTING--Catchment areas of two large teaching hospitals in Glasgow. SUBJECTS--1361 women aged under 75 who had breast cancer diagnosed between 1980 and 1987. MAIN OUTCOME MEASURES--Tumour size, axillary lymph node status, histological grade, and oestrogen receptor concentration in relation to deprivation category of area of residence. RESULTS--There was no significant relation between socioeconomic deprivation and four pathological prognostic factors: 93 (32%) women in the most affluent group presented with tumours less than 20 mm in size compared with 91 (31%) women in the most deprived group; 152 (48%) of the most affluent group presented with negative nodes compared with 129 (46%) of the most deprived group; 23 (22%) of the most affluent group presented with grade I tumours compared with 12 (17%) of the most deprived group; and 142 (51%) of the most affluent group had a low oestrogen receptor concentration at presentation compared with 148 (52%) of the most deprived group. None of these differences was statistically significant. CONCLUSIONS--Differences in survival from breast cancer by socioeconomic deprivation category could not be accounted for by differences in tumour stage or biology. Other possible explanations, such as differences in treatment or in host response, should be investigated. 相似文献
4.
5.
cDNA clones coding for the structural subunit of a chicken brain nicotinic acetylcholine receptor 总被引:7,自引:0,他引:7
Nicotinic acetylcholine receptors (AChRs) immunoaffinity-purified from brains are composed of only two kinds of subunits rather than the four kinds present in muscle-type AChRs. Here we report the N-terminal protein sequences of the structural subunits of AChRs from rat and chicken brains and the cloning of full-length cDNAs for the chicken brain AChR structural subunit. Previously, the N-terminal amino acid sequence of the ACh-binding subunit of AChR immunoaffinity-purified from rat brain was shown to correspond to the cDNA alpha 4. Thus, cDNA sequences are now known for both of the subunits that form one AChR subtype in vivo. 相似文献
6.
The spoOB and spoIVF loci are contiguous on the chromosome of Bacillus subtilis, so that genes in these loci may be parts of a single polycistronic operon. Temperature-sensitive strains having mutations in these loci were isolated, and temperature-shift experiments were carried out to investigate expression of the genes. The temperature-sensitive periods of spoOB mutants extended from the beginning of sporulation until the end of the stage II. The temperature-sensitive periods of spoIVF strains were during stage IV of sporulation. Therefore, although the spoOB and spoIVF loci are contiguous on the chromosome it is unlikely that genes in them are parts of a single polycistronic operon. 相似文献
7.
Shear-oriented Microfibrils in the Mucilaginous Investments of Two Motile Oscillatoriacean Blue-Green Algae 总被引:8,自引:4,他引:4 下载免费PDF全文
Hayes C. Lamont 《Journal of bacteriology》1969,97(1):350-361
Trichomes of two oscillatoriacean blue-green algae execute screw-like gliding motion, but the two organisms differ from each other with respect to the screw sense of motion. Electron microscopy of serial longitudinal sections reveals extracellular microfibrils which lie roughly parallel to stream-lines at the surface of each organism. The author proposes that the microfibrils are oriented by shear in a zone just external to the outer unit membrane-like component of the cell wall. 相似文献
8.
A method for measuring xylem hydraulic conductance and embolism in entire root and shoot systems 总被引:12,自引:6,他引:6
Current methods for determining the influence of xylem cavitationon hydraulic conductance are limited to unbranched stem or rootsegments with hydraulic conductances above c. 2 mmol s1MPa1. Lower conductances and/or highly branched systemsare encountered in seedlings, arid-land shrubs, herbs, and distalportions of shoot and root systems of trees. In order to quantifythe hydraulic impact of cavitation in such systems, existingtechniques have been modified. Branched shoot or root systemswere prepared for measurement by removal of leaves, or roottips, respectively. The shoot or root system was enclosed ina vacuum chamber with the proximal end protruding and suppliedwith perfusing solution. Flow through the xylem was inducedby chamber vacuum. Hydraulic conductance was determined fromthe slope of the flow rate versus pressure relationship. Xylemembolism was quantified from the increase in hydraulic conductancefollowing high pressure (100 kPa) perfusion of solution throughthe plant. Examples are provided of the application of the methodto cavitation studies in the cold desert shrub Artemisia tridentata. Key words: Hydraulic conductance, xylem cavitation, embolism, whole root/shoot system 相似文献
9.
10.
David M. Richardson Richard M. Cowling Byron B. Lamont 《Biodiversity and Conservation》1996,5(9):1035-1046
This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes. 相似文献