Short and long range functions of amino acids in the transmembrane region of the sarcoplasmic reticulum ATPase. A mutational study

Mutational analysis of several amino acids in the transmembrane region of the sarcoplasmic reticulum ATPase was performed by expressing wild type ATPase and 32 site-directed mutants in COS-1 cells followed by functional characterization of the microsomal fraction. Four different phenotype characteristics were observed in the mutants: (a) functions similar to those sustained by the wild type ATPase; (b) Ca2+ transport inhibited to a greater extent than ATPase hydrolytic activity; (c) inhibition of transport and hydrolytic activity in the presence of high levels of phosphorylated enzyme intermediate; and (d) total inhibition of ATP utilization by the enzyme while retaining the ability to form phosphoenzyme by utilization of P(i). Analysis of experimental observations and molecular models revealed short and long range functions of several amino acids within the transmembrane region. Short range functions include: (a) direct involvement of five amino acids in Ca2+ binding within a channel formed by clustered transmembrane helices M4, M5, M6, and M8; (b) roles of several amino acids in structural stabilization of the helical cluster for optimal channel function; and (c) a specific role of Lys297 in sealing the distal end of the channel, suggesting that the M4 helix rotates to allow vectorial flux of Ca2+ upon enzyme phosphorylation. Long range functions are related to the influence of several transmembrane amino acids on phosphorylation reactions with ATP or P(i), transmitted to the extramembranous region of the ATPase in the presence or in the absence of Ca2+.

Acidocalcisomes in Toxoplasma gondii tachyzoites

Toxoplasma gondii tachyzoites were loaded with the fluorescent indicator fura 2 to investigate the transport mechanisms involved in maintaining their intracellular Ca2+ homoeostasis. The mitochondrial ATPase inhibitor oligomycin and the endoplasmic-reticulum Ca(2+)-ATPase inhibitor thapsigargin increased the intracellular Ca2+ concentration ([Ca2+]i), thus indicating the requirement for ATP and the involvement of the endoplasmic reticulum in maintaining intracellular Ca2+ homoeostasis. The effect of thapsigargin was more accentuated in the presence of extracellular Ca2+, clearly showing that, as occurs with other eukaryotic cells, depletion of intracellular Ca2+ pools led to an increase in the uptake of Ca2+ from the extracellular medium. In addition to these results, we found evidence that, in contrast with what occurs in mammalian cells, T. gondii tachyzoites possess a significant amount of Ca2+ stored in an acidic compartment, termed the acidocalcisome, as indicated by: (1) the increase in [Ca2+]i induced by bafilomycin A1 (a specific inhibitor of H(+)-ATPases), nigericin (a K+/H+ exchanger) or the weak base NH4Cl, in the nominal absence of extracellular Ca2+ to preclude Ca2+ entry; and (2) the effect of ionomycin, a Ca(2+)-releasing ionophore that cannot take Ca2+ out of acidic organelles and that was more effective after alkalinization of these compartments by addition of bafilomycin A1, nigericin or NH4Cl. Considering the relative importance of the ionomycin-releasable and the ionomycin + NH4Cl-releasable Ca2+ pools, it is apparent that T. gondii tachyzoites contain a significant amount of Ca2+ stored in acidocalcisomes.

Construction of a brewing yeast having glucoamylase activity and its fermentation characteristics

The brewing yeast having glucoamylase activity was constructed by integrating glucoamylase cDNA from Asapergillus niger into the genome of brewing yeast B48. The integration was achieved by cotransformation of YEP type plasmid pKG1 carrying glucoamylase expression-secretion element and was verified by Southern blot analysis. The engineered yeast was stable, and the fermentation test demonstrated that the lower residual dextrin level was obtained compared with control strain B48. Thus the fermentation rate was raised to 80.5%. No alteration of growth and brewing properties was observed. Beer quality was judged to be good.

Design and synthesis of amphipathic antimicrobial peptides

A large proportion of antimicrobial peptides share a common structural feature that is critical to their antimicrobial activity, i.e. amphipathic alpha-helices. The amphipathy of a polypeptide chain can be quantitated through the value of the hydrophobic moment. Generally, antimicrobial peptides are characterized by high hydrophobic moment and low hydrophobicity values. Using these criteria we have identified two short segments that possess hydrophobic moment properties associated with known antimicrobial peptides. Using in vitro assays the segment derived from the protein perforin displays no antifungal or antibacterial activity and, while showing no alpha-helicity in buffer or liposomes, exhibits a modest degree of alpha-helical structure in the presence of the alpha-helical inducer, 2,2,2-trifluoroethanol. However, rational modifications result in a derivative which assumes an alpha-helical conformation in the presence of liposomes, exhibits potent antifungal activity against plant fungal pathogens, has significant antibacterial activity, effects leakage of a fluorescent dye from acidic liposomes and is devoid of hemolytic activity. Results are also presented for a segment derived from the human immunodeficiency virus envelope protein. We suggest that the identification of putative amphipathic structures in proteins may provide a useful starting strategy in the design and synthesis of antimicrobial peptides.

Serodiagnosis of Asian leishmaniasis with a recombinant antigen from the repetitive domain of a Leishmania kinesin

rK39 is a recombinant product of the 39 amino acid repeats found in a kinesin-like gene of visceral Leishmania spp. This and other antigens were compared for immunodiagnostic potential by enzyme-linked immunosorbent assay with sera from confirmed cases of Asian cutaneous and visceral leishmaniasis. In preliminary trials, rK39 proved superior to 2 purified Leishmania antigens, a cytosolic protein (p36) and a membrane protein (gp63), for immunodiagnosis of visceral leishmaniasis. Of the 53 visceral cases from China and Pakistan assayed, 52 were seropositive (98%) at a 10(-1) dilution with 36 ng of rK39. End point titrations of 27 highly positive samples yielded anti-rK39 antibody titres ranging from c. 10(-3) to beyond 10(-4). Antigen titrations with one positive serum further revealed that rK39 was 25-fold more sensitive than Leishmania whole cell soluble lysates. 31 cutaneous leishmaniasis cases from Turkey assayed for anti-rK39 antibody gave reactions ranging from negative or marginally positive to positive. In Brazil, all cutaneous and mucocutaneous leishmaniasis cases gave negative results in this assay.

[Isolation and sequencing of glucoamylase gene from a glucoamylase over producing strain]

Chromosomal DNA was isolated from the mycelia of Aspergillus niger T21, a strain producing glucoamylase at a high level. Southern blot analysis indicated that the glucoamylase gene is situated on a 2.5kb EcoR I -EcoR V fragment. Chromosomal DNA was digested completely with EcoR I, EcoR V. The fragments in the range of 2.0-3.0kb were isolated through electrophoresis in agarose gel. The pooled fragments were ligated onto pBR322 vector prior to transformation into E. coli DH5. Four glucoamylase-specific recombinants were screened by in situ hybridization from the transformants. Restriction mapping and sequencing for one of the four were performed. Data show that the glucoamylase gene from A. niger T21 is a 2.3kb fragment containing four intervening sequences in the coding region.

Separation of Chinese Leishmania isolates into five genotypes by kinetoplast and chromosomal DNA heterogeneity

Leishmaniasis remains endemic in China, especially in the west and northwest frontier regions in central Asia. Epidemic outbreaks of both visceral and cutaneous forms of the disease have become a serious concern in view of such events occurring in neighboring countries. In the present study, we have begun to characterize available parasites as an initial step in understanding the epidemiology of leishmaniasis in central Asia. Nineteen Leishmania isolates collected since the 1950s from epidemiologically different foci in China were separated into five genotypes (Groups I-V) based on their polymorphisms in both kinetoplast (kDNA) and nuclear (nDNA) DNAs. Both kDNA and nDNA are conserved in Group I, which consists of six isolates, i.e., five cases of human kala-azar and one case of canine leishmaniasis isolated from three distant foci more than 30 years apart. In contrast, both kDNA and nDNA are heterogeneous in Group II, consisting of 10 isolates scattered in the plain area from the eastern coast to the western desert. This group includes five kala-azar cases, one post-kala-azar dermal leishmaniasis case, two sand fly isolates, and two canine isolates. The remaining three groups (III-V), two from great gerbils (Rhombomys opimus) and one from a kala-azar case, differ among themselves and from the aforementioned groups. Groups I, II/III, IV, and V contain isolates that have been recognized epidemiologically or typed isoenzymatically as L. donovani s.l., L. infantum s.l., L. turinica, and L. gerbilli, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Optoelectronic implementation of a compression-attraction-sphere associative memory using an optical spatial pattern-encoding method

A compression-attraction-sphere associative-memory model is proposed. An optoelectronic implementation of its inner-product architecture using an optical spatial pattern-encoding method is demonstrated bycomputer simulations and preliminary experiments.

Environment affects amino acid preference for secondary structure

Three equivocal amino acid sequences were synthesized that are predicted to be alpha-helical from amino acid preference but are found to be primarily beta-strand from x-ray diffraction of their respective proteins. In some solvent systems we recover the alpha-helical structure predicted by amino acid preference, whereas in other systems we mimic the interior of the protein and produce a beta-strand. These results are experimental proof that the environment is important in determining the secondary structure formed by an amino acid sequence; therefore schemes that predict secondary structure from amino acid sequence alone can never be totally successful.

[Investigation on high risk factors of neonatal necrotizing enterocolitis]

In order to evaluate the factors in high-risk neonatal necrotizing enterocolitis (NEC) and predict the prognosis of NEC, a retrospective analysis of 32 factors was made in 42 neonates with NEC. The cases were divided into a low-risk (survival) group and a high-risk (death) group. Of 32 factors compared between these two group, eight were found to be of significance in evaluating the severity of NEC, and six of them were used in the development of a NEC scores (1) number of days before beginning of artificial feeding; (2) neonatal asphyxia or distress; (3) immature form in WBC differential; (4) CO2 combining power; (5) abdominal tenderness; (6) presence of portal vein air (PVA). All laboratory values and physical and radiographic signs were collected during initial presentation of NEC. Neonates with a score of 3 or more are at an increased risk of developing severe NEC with a 83% mortality.

[Various methods for purification of urine Tamm-Horsfall protein]

The measurements of serum, urine Tamm-Horsfall protein (THP) and its antibody are essential to the early diagnosis of tubulointerstitial diseases and acute rejection after renal transplantation. The purification of THP proves to be the key procedure for the production of diagnostic kit. Once, twice and three times salt precipitation with 0.58 mol/L NaCl and chromatography with Sephadax G-200 were adopted to purify urine THP. Enzyme immunoassay was used to detect the antigenicity of the products, SDS-PAGE to determine the molecular weight (MW) and the electrophoretic purity (EP), Beckman DU-7 model spectrophotometer to scan the ultraviolet absorption spectrum. Evaluation of the four methods was based on the purity and the antigenicity of the produced THP, the output, the complexity of procedure, and the cost of required materials. Results show that the MW of THP is 93.0 kd; the ultraviolet absorption maximum is at lambda = 278 nm; the outputs are 7.5, 5.5, 3.8, and 0.4 mg/L; the concentrations of THP with antigenicity are 65%, 75%, 98% and 100%, respectively, and the EPs of three times salt precipitation and chromatography are better. It is concluded that three times salt precipitation should be recommended because of its excellence in purity and antigenicity of the produced THP, the simplicity of manipulation, and the cheapness of the materials needed.