人和小鼠血清DNA结合蛋白质的比较研究

血清DNA结合蛋白质中的某些成分与肿瘤有关。因此我们对人及小鼠血清DNA结合蛋白质作了对比研究。发现两者在蛋白质组成,分子量,等电点及氨基酸组成上颇为相近。但免疫扩散试验证实两者无免疫交叉反应。     

Nearest-neighbor classifier as a tool for classification of protein families

Knowledge about protein function is essential in understanding the biological processes. A specific class or family of protein shares common structural and chemical properties amongst its member sequences. The set of properties that display its unique characteristics for clearly classifying a protein sequence into its corresponding protein family needs to be studied. Our study of these important properties conducted on four major classes of proteins namely Globins, Homeoboxes, Heat Shock proteins (HSP) and Kinase have shown that frequency of twenty naturally occurring amino acids, hydrophobic content of protein, molecular weight of protein, isoelectric point of protein, secondary structure composition of amino acid residues as helices, coils and sheets and the composition of helices, coils and sheets in the secondary structure topology plays a significant role in correctly classifying the protein into its corresponding class or family as indicated by the overall efficiency of Nearest Neighbor Classifier as 84.92%.     

Synaptonemal Complex Proteins: Specific Proteins of Meiotic Chromosomes

The review considers proteins of the synaptonemal complex (SC), a specific structure formed between homologous chromosomes in maturing germline cells during meiotic prophase I. The structure and functions are described for proteins that form ultrastructural SC elements in mammals, in yeast, and in higher plants. The roles of cohesins and of the SC proteins in meiotic sister-chromatid cohesion are considered. Though still scarce, data are summarized on the SC self-assembly and dissociation and on the molecular composition of SC-associated recombination nodules, which provide a compartment for meiotic recombination enzymes. The accumulating data on the SC molecular components and on their structure, properties, and interactions improve the understanding of the SC function.     

Age-Dependent Changes in the Ultrastructure and in the Molecular Composition of Rat Brain Microtubules

An age-dependent increase of a cathepsin D-like protease activity that preferentially degrades high molecular weight microtubule-associated proteins (MAPs) has been previously described. Microtubules (MT) purified from rat brain of different ages in the presence of several protease inhibitors retained undegraded MAPs through cycles of polymerization, and revealed several age-dependent changes in the relative amounts of MAPs and MT-associated kinases. MAP2 immunoreactivity was found significantly lower in MT preparations from aged animals in contrast with a relative increase of tau molecules. In addition, the phosphorylation of MAP2 by its associated cyclic AMP-dependent protein kinase was also altered, consecutively to the partial loss of the enzyme during polymerization cycles and an age-dependent decrease in the ability of the cyclic nucleotide to stimulate MAP2-bound kinase activity. The evidence of an unusually high packing density of sedimented MT from old rat brains further suggested the modification with aging of the physical structure of the arm-like projections of MAPs, in addition to a lower amount in high molecular weight MAPs. These results support the hypothesis of a selective alteration with aging of the mechanical and regulatory properties of brain MT, consecutive to a change in the composition and/or the structure of MAPs.     

Structure characterization of the central repetitive domain of high molecular weight gluten proteins. II. Characterization in solution and in the dry state.

The structure of the central repetitive domain of high molecular weight HMW) wheat gluten proteins was characterized in solution and in the dry state using HMW proteins Bx6 and Bx7 and a subcloned, bacterially expressed part of the repetitive domain of HMW Dx5. Model studies of the HMW consensus peptides PGQGQQ and GYYPTSPQQ formed the basis for the data analysis (van Dijk AA et al., 1997, Protein Sci 6:637-648). In solution, the repetitive domain contained a continuous nonoverlapping series of both type I and type II II beta-turns at positions predicted from the model studies; type II beta-turns occurred at QPGQ and QQGY sequences and type I beta-turns at YPTS and SPQQ. The subcloned part of the HMW Dx5 repetitive domain sometimes migrated as two bands on SDS-PAGE; we present evidence that this may be caused by a single amino acid insertion that disturbs the regular structure of beta-turns. The type I beta-turns are lost when the protein is dried on a solid surface, probably by conversion to type II beta-turns. The homogeneous type II beta-turn distribution is compatible with the formation of a beta-spiral structure, which provides the protein with elastic properties. The beta-turns and thus the beta-spiral are stabilized by hydrogen bonds within and between turns. Reformation of this hydrogen bonding network after, e.g., mechanical disruption may be important for the elastic properties of gluten proteins.     

Molecular basis for the special properties of proteins and enzymes from Halobacterium marismortui

Abstract Three proteins from Halobacterium marismortui , malate dehydrogenase (hMDH), glutamate dehydrogenase (hGDH) and ferredoxin (hFD) were purified and characterized with respect to their molecular masses, amino acid composition and, for hFD only, primary structure. Striking features of halophilic proteins are: the high excess of acidic over basic residues; acidic clusters in the sequence. Low-salt concentration causes inactivation and changes in structural parameters of hMDH and hGDH. Reactivation of hMDH involves long-lived stable intermediates. The salt concentration optimum of enzymic activity is independent of salt nature. The high capacity of halophilic proteins to retain water and salt is due to unique molecular properties, studied by physico-chemical techniques.     

Nonerythrocyte spectrins: actin-membrane attachment proteins occurring in many cell types

The properties of brain fodrin have been analyzed and compared with those of erythrocyte spectrin. Both proteins consist of high molecular weight polypeptide doublets on SDS polyacrylamide gels and in solution behave as very large asymmetric molecules. Both proteins show a characteristic increase in sedimentation coefficient in the presence of 20 mM KCl. Antibodies against the brain protein cross-react with erythrocyte spectrin and cross-react with similar high molecular weight doublet polypeptides in SDS polyacrylamide gels of other cell types and plasma membrane preparations. Both proteins bind actin. The brain protein and erythrocyte spectrin show specific and competitive binding to erythrocyte membranes and this binding is inhibited by antibodies against erythrocyte ankyrin. Several of these properties distinguish these proteins from the class of high molecular weight actin-binding proteins that includes filamin and macrophage actin-binding protein. We conclude that together with erythrocyte spectrin, the brain protein and equivalent, immunologically related proteins in other cell types belong to a single class of proteins with the common function of attachment of actin to plasma membranes. Based on the structural and functional similarities, the name spectrin would seem appropriate for this whole class of proteins.     

Purification of mammalian filamin. Similarity to high molecular weight actin-binding protein in macrophages, platelets, fibroblasts, and other tissues

We have purified the high molecular weight actin-binding protein, filamin from guinea pig vas deferens. We find this mammalian filamin is very similar to chicken gizzard filamin in subunit molecular weight, amnio acid composition, actin-binding properties, immunological cross-reactivity, and the ability to be phosphorylated by cyclic AMP-dependent protein kinase. Anti-filamin antibodies cross-react with a high molecular weight macrophage actin-binding protein, and with a high molecular weight protein in platelets and fibroblasts. Furthermore like filamin, these proteins are also phosphorylated and cyclic AMP stimulates their phosphorylation. Anti-filamin antibodies do not cross-react with the erythrocyte membrane protein spectrin or with high molecular weight proteins in brain extracts. We conclude that filamin from avian and mammalian smooth muscle are very similar proteins and furthermore that many, but not all, non-muscle cells contain a protein closely related to filamin.     

Polymerized and polyethylene glycol-conjugated hemoglobins: A globin-based calibration curve for dynamic light scattering analysis

Dynamic light scattering (DLS) is a technique capable of determining the hydrodynamic radius of proteins. From this parameter, a molecular weight can be assessed provided that an appropriate calibration curve is available. To this goal, a globin-based calibration curve was used to determine the polymerization state of a recombinant hemoglobin-based oxygen carrier and to assess the equivalent molecular weight of hemoglobins conjugated with polyethylene glycol molecules. The good agreement between DLS values and those obtained from gel filtration chromatography is a consequence of the high similarity in structure, shape, and density within the globin superfamily. Moreover, globins and heme proteins in general share similar spectroscopic properties, thereby reducing possible systematic errors associated with the absorption of the probe radiation by the chromophore.     

Interaction between proteins and glucosinolate isothiocyanates and oxazolidinethiones from Brassica napus seed

The proteins from rape seed meal and serum albumin were incubated with the ³⁵S-labelled glucosinolates progoitrin, gluconapin, and glucoalyssin in a variety of reaction conditions. Intact glucosinolates and oxazolidinethiones were found to combine with the proteins to a very small extent, independently of pH; but the isothiocyanates reacted readily with the proteins at pH values higher than 6. Fractionation of the rape seed protein conjugates on Sephadex G200 showed that isothiocyanates particularly reacted with the basic low molecular weight proteins. Changes in UV-spectrum and electrophoretic mobility after reaction with isothiocyanates were also demonstrated.     

Does Intrinsic Disorder in Proteins Favor Their Interaction with Lipids?

Intrinsically disordered proteins (IDPs) are implicated in a range of human diseases, some of which are associated with the ability to bind to lipids. Although the presence of solvent‐exposed hydrophobic regions in IDPs should favor their interactions with low‐molecular‐weight hydrophobic/amphiphilic compounds, this hypothesis has not been systematically explored as of yet. In this study, the analysis of the DisProt database with regard to the presence of lipid‐binding IDPs (LBIDPs) reveals that they comprise, at least, 15% of DisProt entries. LBIDPs are classified into four groups by ligand type, functional categories, domain structure, and conformational state. 57% of LBIDPs are classified as ordered according to the CH‐CDF analysis, and 70% of LBIDPs possess lengths of disordered regions below 50%. To investigate the lipid‐binding properties of IDPs for which lipid binding is not reported, three proteins from different conformational groups are rationally selected. They all are shown to bind linoleic (LA) and oleic (OA) acids with capacities ranging from 9 to 34 LA/OA molecules per protein molecule. The association with LA/OA causes the formation of high‐molecular‐weight lipid–protein complexes. These findings suggest that lipid binding is common among IDPs, which can favor their involvement in lipid metabolism.     

Protein Compositional Analysis of the Eggs of Black Widow Spider (Latrodectus tredecimguttatus): Implications for the Understanding of Egg Toxicity

Previous work found that high‐molecular‐weight fractions in the egg extract of Latrodectus tredecimguttatus exhibited strong toxicities. For investigating the possible relationship of proteins in the eggs with the toxic effect, the protein composition of the eggs was analyzed using proteomic strategies and compared with that of the spider's venom. SDS‐PAGE showed that the proteins of eggs were primarily distributed in the molecular weight range of higher than 55 kDa as well as around 34 kDa, having high abundance proteins with molecular weights of about 60 kDa and 130 kDa. A total of 157 proteins were identified from the egg extract, which were involved in important cellular functions and processes including catalysis, transport, and metabolism regulation. Comparison indicated that the protein composition of eggs is more complex than that of venom, and there are few similarities between the protein composition of the two materials, demonstrating that the eggs have their own distinct toxic mechanism. © 2012Wiley Periodicals, Inc. J BiochemMol Toxicol 26:510‐515, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21460     

小麦高分子量麦谷蛋白亚基序列及其结构与加工品质的关系

高分子量麦谷蛋白亚基（high molecular weight glutenin subunit,HMW-GS）是小麦种子贮藏蛋白的主要成分,其组成、含量和结构直接影响小麦面粉面筋的弹展性,决定着小麦的加工品质。本文主要对小麦HMW-GS的序列、结构和亚基之间组合形式做了详细的综述,并较系统地讨论了HMW-GS的结构和组成、特点等与面粉的加工品质之间的关系以及如何从定性和定量两方面来影响面粉的加工品质。     

Physicochemical characterization and functional analysis of some snake venom toxin proteins and related non-toxin proteins of other chordates

Snake venom contains a diverse array of proteins and polypeptides. Cytotoxins and short neurotoxins are non-enzymatic polypeptide components of snake venom. The three-dimensional structure of cytotoxin and short neurotoxin resembles a three finger appearance of three-finger protein super family. Different family members of three-finger protein super family are employed in diverse biological functions. In this work we analyzed the cytotoxin, short neurotoxin and related non-toxin proteins of other chordates in terms of functional analysis, amino acid compositional (%) profile, number of amino acids, molecular weight, theoretical isoelectric point (pI), number of positively charged and negatively charged amino acid residues, instability index and grand average of hydropathy with the help of different bioinformatical tools. Among all interesting results, profile of amino acid composition (%) depicts that all sequences contain a conserved cysteine amount but differential amount of different amino acid residues which have a family specific pattern. Involvement in different biological functions is one of the driving forces which contribute the vivid amino acid composition profile of these proteins. Different biological system dependent adaptation gives the birth of enriched bio-molecules. Understanding of physicochemical properties of these proteins will help to generate medicinally important therapeutic molecules for betterment of human lives.     

Characterization of 2S seed storage protein of Brassica campestris and its antigenic homology with seed proteins of other Cruciferae.

The low molecular weight seed storage protein of Brassica campestris has been isolated and its amino acid composition determined. Antibody raised against this low molecular weight protein has been used to compare the antigenic similarity between the low molecular weight storage proteins of different Cruciferae seeds by immunoprecipitation and Western blotting. These studies revealed the existence of antigenically homologous proteins of identical molecular weights in seeds of other Cruciferae but absent in some other dicots like mung bean and tobacco seeds.     

Synthesis of Endosperm Proteins in Wheat Seed during Maturation

The time of synthesis, the molecular weight, and the relative glutamine-glutamate and proline to leucine ratios of the endosperm proteins of wheat (Triticum aestivum L. cv. Logan) were determined using a sodium dodecyl sulfate-polyacrylamide gel technique. In general, synthesis of most proteins occurred through much of the maturation of the seed, but past 20 days the rate of synthesis of the high molecular weight proteins declined more rapidly than those of lower molecular weight. The synthesis of at least one protein occurred only late in seed maturation. Several of the high molecular weight proteins had glutamate-glutamine to leucine ratios higher than the remainder of the proteins. No evidence for proteins of a polyglutamine-glutamate and/or proline nature was found.     

A defective seed coat pattern (Net) is correlated with the post-transcriptional abundance of soluble proline-rich cell wall proteins

The pigmented seed coats of several soybean (Glycine max (L.) Merr.) plant introductions and isolines have unusual defects that result in cracking of the mature seed coat exposing the endosperm and cotyledons. It has previously been shown that the T (tawny) locus that controls the color of trichomes on stems and leaves also has an effect on both the structure and pigmentation of the seed coat. Distribution of pigmentation on the seed coat is controlled by alleles of the I (inhibitor) locus. It was also found that total seed coat proteins were difficult to extract from pigmented seed coats with i T genotypes because they have procyanidins that exhibit tannin properties. We report that the inclusion of poly-L-proline in the extraction buffer out-competes proteins for binding to procyanidins. Once this problem was solved, we examined expression of the proline-rich cell wall proteins PRP1 and PRP2 in pigmented genotypes with the dominant T allele. We found that both homozygous i T and i t genotypes have reduced soluble PRP1 levels. The epistatic interaction of the double recessive genotype at both loci is necessary to produce the pigmented, defective seed coat phenotype characteristic of seed coats with the double recessive i and t alleles. This implies a novel effect of an enzyme in the flavonoid pathway on seed coat structure in addition to its effect on flavonoids, anthocyanidins, and proanthocyanidins. No soluble PRP1 polypeptides were detectable in pigmented seed coats (i T genotypes) of isolines that also display a net-like pattern of seed coat cracking, known as the Net defect. PRP2 was also absent in one of the these lines. However, both PRP1 and PRP2 cytoplasmic mRNAs were found in the Net-defective seed coats. Together with in vitro translation studies, these results suggest that the absence of soluble PRP polypeptides in the defective Net lines is post-translational and could be due to a more rapid or premature insolubilization of PRP polypeptides within the cell wall matrix.     

Changes in liver nuclear sap proteins during chick embryo development

Summary Nuclear sap proteins from liver of 12-, 15-, 19-day-old embryos and 1-day-old chicks were resolved by one-and two-dimensional gel electrophoresis. Although the protein patterns from various stages of development have remarkable similarities, some qualitative and quantitative differences were found among these patterns. The most pronounced changes were detected in protein with molecular weight of 100 K which was very abundant in nuclei of 12-day-old embryos and disappeared in nuclei of older embryos and in protein with molecular weight of 40 K which rapidly diminished after hatching.     

Blue copper proteins: a comparative analysis of their molecular interaction properties

Blue copper proteins are type-I copper-containing redox proteins whose role is to shuttle electrons from an electron donor to an electron acceptor in bacteria and plants. A large amount of experimental data is available on blue copper proteins; however, their functional characterization is hindered by the complexity of redox processes in biological systems. We describe here the application of a semiquantitative method based on a comparative analysis of molecular interaction fields to gain insights into the recognition properties of blue copper proteins. Molecular electrostatic and hydrophobic potentials were computed and compared for a set of 33 experimentally-determined structures of proteins from seven blue copper subfamilies, and the results were quantified by means of similarity indices. The analysis provides a classification of the blue copper proteins and shows that (I) comparison of the molecular electrostatic potentials provides useful information complementary to that highlighted by sequence analysis; (2) similarities in recognition properties can be detected for proteins belonging to different subfamilies, such as amicyanins and pseudoazurins, that may be isofunctional proteins; (3) dissimilarities in interaction properties, consistent with experimentally different binding specificities, may be observed between proteins belonging to the same subfamily, such as cyanobacterial and eukaryotic plastocyanins; (4) proteins with low sequence identity, such as azurins and pseudoazurins, can have sufficient similarity to bind to similar electron donors and acceptors while having different binding specificity profiles.     

Isolation and characterization of Ca2+-dependent modulator protein from the marine invertebrate Renilla reniformis.

An acidic, low molecular weight (18 400--19 100) protein capable of activating porcine brain phosphodiesterase in the presence of calcium has been purified 2700-fold from the anthozoan coelenterate, Renilla reniformis. The protein has physical, spectral, and chemical properties similar to those of modulator proteins isolated from mammalian species. Amino acid composition studies reveal no significant differences between the Renilla and mammalian modulator proteins. For example, we observed 1 mol of epsilon-N-trimethyllysine per mol of protein, no tryptophan or cysteine, and high levels of glutamic and aspartic acid residues. The protein from Renilla complexes with troponin I and T subunits in the presence of calcium and quantitatively replaces porcine brain modulator in the calcium-dependent activation of porcine brain phosphodiesterase. The protein has a high affinity for calcium as judged by the low levels of free calcium required for modulator-dependent activation of phosphodiesterase. The similarities in physical and chemical properties, high affinity for calcium, and identical calcium-dependent activities of this protein from Renilla (as compared with modulator protein purified from mammalian systems) suggest that a high degree of structural conservation has been retained in modulator proteins isolated from these diverse evolutionary forms.