Unfolding of tertiary structure ofHalobacterium halobium flagellins does not result in flagella destruction

The structure ofHalobacterium halobium R₁M₁ flagella is investigated by the methods of scanning microcalorimetry, circular dichroism, and electron microscopy. It is shown that melting curves of flagella in solutions with a different concentration of NaCl display only one peak of heat capacity that corresponds to one cooperatively melting domain. It is found that flagella do not dissociate after melting. The possible structural organization of archaebacterial flagella is discussed.     

Solution properties ofEscherichia coli-expressed VH domain of anti-neuraminidase antibody NC41

The V_H domain of anti-influenza neuraminidase antibody NC41, with and without a C-terminal hydrophilic marker peptide (FLAG^TM), has been expressed in high yield (15–27 mg/L) inEscherichia coli. Both forms were secreted into the periplasm where they formed insoluble aggregates which were solubilized quantitatively with 2 M guanidine hydrochloride and purified to homogeneity by ion-exchange chromatography. The V_H-FLAG was composed of three isoforms (pI values of 4.6, 4.9, and 5.3) and the V_H molecule was composed of two isoforms with pI values of 5.1 and 6.7; the difference between the V_H isoforms was shown to be due to cyclization of the N-terminal glutamine residue in the pI 5.1 isoform. At 20°C and concentrations of 5–10mg/ml the V_H domain dimerized in solution and then partly precipitated, resulting in the broadening of resonances in its¹H NMR spectrum. Reagents such as CHAPS,n-octylglucoside, and ethylene glycol, which presumably mask the exposed hydrophobic interface of the V_H molecule, prevented dimerization of the V_H and permitted good-quality NMR spectra on isotope-labeled protein to be obtained.     

Bifurcation, Bursting, and Spike Frequency Adaptation

Many neural systems display adaptive properties that occur on timescales that are slower than the time scales associated withrepetitive firing of action potentials or bursting oscillations. Spike frequency adaptation is the name givento processes thatreduce the frequency of rhythmic tonic firing of action potentials,sometimes leading to the termination of spiking and the cell becomingquiescent. This article examines these processes mathematically,within the context of singularly perturbed dynamical systems.We place emphasis on the lengths of successive interspikeintervals during adaptation. Two different bifurcation mechanisms insingularly perturbed systems that correspond to the termination offiring are distinguished by the rate at which interspike intervalsslow near the termination of firing. We compare theoreticalpredictions to measurement of spike frequency adaptation in a modelof the LP cell of the lobster stomatogastric ganglion.     

Crystallization and preliminary X-ray diffraction studies of aSFP, a bovine seminal plasma protein with a single CUB domain architecture.

Bovine acidic seminal fluid protein (aSFP) is a 1.29 kDa polypeptide of the spermadhesin family built by a single CUB domain architecture. The CUB domain is an extracellular module present in 16 functionally diverse proteins. To determine the three-dimensional structure of aSFP, the protein was crystallized at 21 degrees C by vapor diffusion in hanging drops, using ammonium sulfate, pH 4.7, and polyethyleneglycol 4,000 as precipitants, containing 10% dioxane to avoid the formation of clustered crystals. Elongated prismatic crystals with maximal size of 0.6 x 0.3 x 0.2 mm3 diffract to beyond 1.9 A resolution and belong to space group P2(1)2(1)2(1), with cell parameters a = 52.4 A, b = 41.5 A, c = 48.2 A. There is one aSFP molecule per asymmetric unit, which corresponds to a crystal volume per unit molecular mass of 2.04 A3/Da, and analytical ultracentrifugation analysis show that aSFP is a monomeric protein.     

Evidence for PDZ domains in bacteria, yeast, and plants.

Several dozen signaling proteins are now known to contain 80-100 residue repeats, called PDZ (or DHR or GLGF) domains, several of which interact with the C-terminal tetrapeptide motifs X-Ser/Thr-X-Val-COO- of ion channels and/or receptors. PDZ domains have previously been noted only in mammals, flies, and worms, suggesting that the primordial PDZ domain arose relatively late in eukaryotic evolution. Here, techniques of sequence analysis-including local alignment, profile, and motif database searches-indicate that PDZ domain homologues are present in yeast, plants, and bacteria. It is suggested that two PDZ domains occur in bacterial high-temperature requirement A (htrA) and one in tail-specific protease (tsp) homologues, and that a yeast htrA homologue contains four PDZ domains. Sequence comparisons suggest that the spread of PDZ domains in these diverse organisms may have occurred via horizontal gene transfer. The known affinity of Escherichia coli tsp for C-terminal polypeptides is proposed to be mediated by its PDZ-like domain, in a similar manner to the binding of C-terminal polypeptides by animal PDZ domains.     

HIV-1 Nef protein: purification, crystallizations, and preliminary X-ray diffraction studies.

Human immunodeficiency virus Nef protein accelerates virulent progression of AIDS by its interaction with specific cellular proteins involved in cellular activation and signal transduction. Here we report the purification and crystallization of the conserved core of HIV-1LAI Nef protein in the unliganded form and in complex with the wild-type SH3 domain of the P59fyn protein-tyrosine kinase. One-dimensional NMR experiments show that full-length protein and truncated fragment corresponding to the product of HIV-1 protease cleavage have a well-folded compact tertiary structure. The ligand-free HIV-1 Nefcore protein forms cubic crystals belonging to space group P23 with unit cell dimensions of a = b = c = 86.4 A. The Nef-Fyn SH3 cocrystals belong to the space group P6(1)22 or its enantiomorph, P6(5)22, with unit cell dimensions of a = b = 108.2 A and c = 223.7 A. Both crystal forms diffract to a resolution limit of 3.0 A resolution using synchrotron radiation, and are thus suitable for X-ray structure determination.     

The X-ray structure of a mutant eye lens beta B2-crystallin with truncated sequence extensions.

beta-Crystallins are oligomeric eye lens proteins that are related to monomeric gamma-crystallins by domain swapping: like gamma-crystallins, they are comprised of two similar domains but they differ in having long sequence extensions. beta B2, a major component of beta-crystallin oligomers, self-associates to a homodimer in solution. In two crystal structures of native beta B2, the protein is a 222-symmetric tetramer of eight domains. It has previously been shown that a mutant of rat beta B2-crystallin, in which the bulk of the N- and C-terminal sequence extensions has been deleted, assembles into dimers and tetramers. Here we present the 3.0 A resolution X-ray structure of the tetramer, beta B2 delta NC1. The mutant tetramer has a very similar set of domain interactions to the native structure. However, the structures differ in the relative orientation of the two sets of four domains. The paired N- and C-terminal domain interface, which is at the heart of the dimer structure, is very similar to the native structure. However, the truncation of the C-terminal extension removes an important tryptophan residue, which prevents the extension from acting as a (non-covalent) linker, as it does in native beta B2. There is a knock-on structural effect that removes a contact between extension and covalent linker, and this appears to cause a small twist in the linker that is amplified into a 20 degrees rotation between sets of paired domains.     

原生质体电融合酵母多倍体生理特性的研究

对原生质体电融合技术获得的11株酵母多倍体融合株,进行了一系列生理特性的分析比较．结果发现,在电融合过程中,融合株的细胞体积及DNA含量并不随着核倍性呈线性递增．而是有其特殊的变化规律。当糖化酵母sta1、sta2和sta3在细胞核中各自纯合时,明显表现出表达的剂量效应。其中sta1、sta2纯合的融合株．在YEPS培养中,GA分泌可被淀粉大量诱导,表现出一定的二次生长特性。从分析结果推测,在亲株5301-14D及HU-TY—1A中可能有对GA分泌不利的因素。     

异色芋生物学特性观察

本文对观赏植物异色芋（ＣｏｌｏｃａｓｉａｈｅｔｅｒｏｃｈｒｏｍａＨ．ＬｉｅｔＺ．Ｘ．Ｗｅｉ）在昆明栽培环境下的生物学特性进行总结,为商品化栽培异色芋提供了理论依据,为其分类也提供了一定的有益补充。结果表明：一年生植株不开花,根茎也不产生分枝;二年生植株开花率为７３．６％,根茎平均分枝３．６条。异色芋３月上旬开始萌动,７月中旬抽花梗,８月上旬开花,１１月份地上部分枯萎,因此在昆明异色芋生育期约２６０ｄ。     

甜味蛋白研究的新进展

甜味蛋白(thaumatin)是世界上已知最甜的物质,具有很大的应用前景.Thaumatin的基因核苷酸和蛋白质氨基酸序列都已测定.晶体分析表明它具有高稳定的四级结构.在味蕾小孔中发现了介导thaumatin发生作用的物质.Thaumatin自身的功能仍不清楚.在多种生物中发现了thaumatin类似蛋白质,具有不同的生物活性.用基因工程手段实现了thaumatin在多种原核和真核生物中的表达,但迄今仍未得到理想的基因工程产品.