Peptide binding domains determined through chemical modification of the side-chain functional groups.

A clear understanding of the specific secondary structure and binding domain resulting from the interactions of proteins and peptides with lipid surfaces will provide insight into the specific functions of biologically active molecules. We have shown in earlier studies that the stationary phases used in reverse-phase high-performance liquid chromatography represent a model artificial lipid surface for the study of induced conformational states of peptides on lipid interaction. We have now used reverse-phase high-performance liquid chromatography to determine the binding domains of peptides and, by extension, of proteins to a lipid surface. This approach consists of performing chemical modifications of specific amino acid side-chain functionalities after the interaction of the peptides with the reverse-phase high-performance liquid chromatography C18 groups. The susceptibility to oxidation was also studied after binding of the same peptides to liposomes. Oxidation of a single methionine residue "walked" through an amphipathic alpha-helical 18-mer peptide was selected to illustrate this approach. The extent of oxidation was found to be clearly dictated by the accessibility of the methionine residue to the aqueous mobile phase. The binding domain found for the peptide in its lipid-induced conformational state was unequivocally the entire hydrophobic face of the amphipathic alpha-helix.     

The stability and functional properties of proteoliposomes mixed with dextran derivatives bearing hydrophobic anchor groups.

Liposomes composed of Escherichia coli phospholipid were coated with polysaccharides bearing hydrophobic palmitoyl anchors. The effect on the stability of liposomes without or with integral membrane proteins was investigated. A high concentration of hydrophobized dextrans protected the liposomes against detergent degradation, decreased the fluidity of the membranes, prevented fusion of the liposomes and enhanced their stability. Proteoliposomes containing beef heart cytochrome-c oxidase and the lactose transport carrier of E. coli were similarly affected by coating with the dextrans. Under these conditions both membrane proteins were still active. Long-term stability of the coated liposomes was obtained only in the absence of the integral membrane proteins.     

Cesium cholate: determination of X-ray crystal structure indicates participation of the ring hydroxyl groups in metal binding

The crystal structure of cesium cholate, C(24)H(36)(OH)(3) COOCs has been determined with three-dimensional X-ray diffractometer data. It crystallized in the monoclinic space group P2(1) with unit-cell dimensions a = 11.543(5) A, b = 8.614(3) A, and c = 12.662(5) A, beta(deg) = 107.95(2), V = 1197.7 A(3) and Z = 2. The atomic parameters were refined to a final r = 0.0269 and R(omega) = 0.0280 for 2342 observed reflections. Each Cs(+) is coordinated to 7 oxygen atoms from 5 different cholate anions with Cs-O distances ranging from 2.957(4) A to 3.678(5) A. In this crystal, 5 cholates are coordinated with 1 Cs(+), and 5 Cs(+) are coordinated with 1 cholate anion. Carboxyl and all the 3 ring hydroxyl groups of cholate anion participate in binding to Cs(+) simultaneously, and there is no water molecule coordinated with the Cs(+). The pattern of successive rows arranged with polar (p) and non-polar (n) faces in apposition leads to the formation of a sandwich sheet structure with polar and non-polar channels. The Cs ions lie within the polar interior of the sandwich. The H-bond network is reorganized in forming cesium cholate from cholic acid. All the oxygen atoms in cholate anion are involved in H-bonding reciprocally or with water molecules to form an extensive 3-dimensional network of H-bonds. Compared with cholic acid and other similar type of steroids, the coordination structure and H-bonding of Cs cholate crystal are distinct.     

Influence of functional groups on the in vitro anticoagulant activity of chitosan sulfate

A new method for the chemical modification of chitosan sulfate was used to prepare N-propanoyl-, N-hexanoyl- and N,O-quaternary substituted chitosan sulfate. Structural analysis by elemental analysis, FTIR, 13C NMR, and 1H NMR spectroscopy, and gel-permeation chromatography showed that these methods could conveniently be used for the introduction of functional groups. The influences of the acyl or quaternary groups on the anticoagulant activity of the polysaccharides were studied with respect to activated partial thromboplastin time (APTT) thrombin time (TT), and prothrombin time (PT). The propanoyl and hexanoyl groups increased the APTT activity, and the propanoyl groups also increased the TT anticoagulant activity slightly, while the N,O-quaternary chitosan sulfate showed only a slight TT coagulant activity.     

A competitive labeling method for the determination of the chemical properties of solitary functional groups in proteins.

The properties of the functional groups in a protein can be used as built-in-probes of the structure of the protein. We have developed a general procedure whereby the ionization constant and chemical reactivity of solitary functional groups in proteins may be determined. The method may be applied to the side chain of histidine, tyrosine, lysine, and cysteine, as well as to the amino terminus of the protein. The method, which is an extension of the competitive labeling technique using [3H]- and [14C]1-fluoro-2,4-dinitrobenzene (N2ph-F) in a double-labeling procedure, is rapid and sensitive. Advantage is taken of the fact that after acid hydrolysis of a dinitrophenylated protein, a derivative is obtained which must be derived from a unique position in the protein. The method has been applied to the solitary histidine residue of lysozyme, alpha-lytic protease, and Streptomyces griseus (S.G.) trypsin, as well as to the amino terminus of the latter protein. The following parameters were obtained for reaction with N2ph-F at 20 degrees C in 0.1 N KCl: the histidine of hen egg-white lysozyme, pKa of 6.4 and second-order velocity constant of 0.188 M-1 min-1; the histidine of alpha-lytic protease, pKa of 6.5 and second-order velocity constant of 0.0235 M-1 min-1; the histidine of S.G. trypsin, pKa of 6.5 and second-order velocity constant of 0.0328 M-1 min-1; the valyl amino terminus of S.G. trypsin, pKa of 8.1 and second-order velocity constant of 0.403 M-1 min-1. In addition, the results obtained provide clues as to the microenvironments of these functional groups, and indicate that the proteins studied undergo pH-dependent conformational changes which affect the microenvironment, and hence the chemical reactivity of these groups.     

基于功能类群分析呼兰河口湿地浮游植物群落结构特征

浮游植物对水环境条件变化敏感,其群落演替特征被广泛应用于指示水环境变化。基于3种浮游植物功能类群方法,对呼兰河口湿地浮游植物群落结构进行研究。于2018年春季（4、5月）、夏季（6、7、8月）和秋季（9、10月）三季,在呼兰河口湿地共设置11个采样点,通过ASNOSIM和SIMPER分析探索FG、MFG和MBFG功能类群的演替特征,基于RDA分析阐述功能类群对环境因子的响应模式。研究期间共鉴定浮游植物243个分类单位,隶属于7门9纲18目32科75属;其种类组成主要以绿藻门（46.09%）、裸藻门（19.34%）和硅藻门（18.52%）为主。共划分FG功能类群25个,MFG功能类群20个,MBFG功能类群6个;ANOSIM分析表明不同季节之间FG和MFG功能类群结构差异显著;SIMPER分析表明S1/Lo/W1/P/J/Y、9b/5a/11b/6a/2c/2d/1c和Ⅲ/Ⅰ类群是影响不同季节之间功能类群变化的主要类群;RDA分析表明,FG、MFG和MBFG功能类群的演替受多种环境因素共同影响,其中pH、BOD₅、Tur.和COD_Mn与功能类群演替关系密切。相较于MBFG功能类群,FG和MFG功能类群能更好的响应呼兰河口湿地水环境的空间异质性。     

Influence of functional groups on homologous antibody affinity of 11 alpha-hydroxyprogesterone derivatives. I. Synthesis and affinity evaluation

Syntheses and cross-reactivities with progesterone toward the same specific antibody are reported for a series of amides of 11 alpha-hydroxyprogesterone 11-hemisuccinate. Some hypotheses are made regarding the effects of the chemical structure of the substituents on the immunological properties of derivatives.     

Chemical properties of the functional groups of insulin.

The method of competitive binding [Kaplan, Stevenson & Hartley (1971) Biochem. J. 124, 289-299] with 1-fluoro-2,4-dinitrobenzene as the labelling reagent [Duggleby & Kaplan (1975) Biochemistry 14, 5168-5175] was used to determine the chemical properties, namely pK and reactivity, of the amino groups, the histidine residues and the tyrosine residues of the dimeric form of pig zinc-free insulin at 20.0 degrees C. The N-terminal glycine residue of the A-chain has a pK of 7.7 and a slightly higher than normal reactivity. The N-terminal phenylalanine residue of the B-chain has a pK of 6.9 and is approximately an order of magnitude more reactive than a corresponding amino group with the same pK value. The lysine epsilon-amino group has an unusually low pK of 7.0 but has approximately the expected reactivity of such a group. In the case of the two histidine and four tyrosine residues only the average properties of each class were determined. The histidine residues have a pK value of approx. 6.6, but, however, their reactivity is at least an order of magnitude greater than that of a free imidazole group. The tyrosine residues have a pK value of approx. 10, but their average reactivities are substantially less than for a free phenolic group. At alkaline pH values above 8 the reactivity of all the functional groups show sharp discontinuities, indicating that insulin is undergoing a structural change that alters the properties of these groups.     

Influence of lipophilic groups in cationic alpha-helical peptides on their abilities to bind with DNA and deliver genes into cells.

For the purpose of achieving gene transfer into cells mediated by peptides with a short chain length, we employed two kinds of amphiphilic alpha-helix peptides, mastoparan (INLK-ALAA-LAKK-IL-NH2) obtained from wasp venom and an alpha-helix model peptide (LARL-LARL-LARL-NH2). Furthermore, to strengthen the hydrophobicity of the peptide required for the formation of the aggregates with the DNA, we modified these peptides using several lipophilic groups, i.e. acyl groups with a single chain, a dialkylcarbamoyl group and a cholesteryloxycarbonyl group. We examined the ability of the peptides and their derivatives to bind and aggregate with plasmid DNA, the structural change in the peptides caused by binding with the DNA and the in vitro gene transfer abilities into COS-7 cells. As a result, mastoparan was found to acquire the DNA binding ability by introduction of the lipophilic group. The conformational change in the peptides depended on the hydrophobicity of the introduced acyl group. The DNA complex of most lipophilic mastoparan derivatives could be incorporated into the cells via the endocytosis pathway. In the case of the helix model peptide, the acyl group with a moderate chain length was required for the formation of the aggregate which is competent for incorporation into the cells. In this study, we succeeded in giving such short peptides sufficient gene transfer ability by modifying them with some lipophilic groups. However, the influence of the modification by the lipophilic groups on the formation of aggregates with DNA and the gene transfer ability depended on the structure of the peptide portion. These results indicate that consideration of total hydrophobicity balance is needed for the design of an efficient gene carrier peptide.     

Local and regional determinants of stream fish assemblage structure: inferences based on taxonomic vs. functional groups

Aim  To examine the roles of local and regional environmental variables and biotic interactions in determining the structure of local stream fish assemblages, and to compare results derived from analyses based on taxonomic and functional groups.
Location  Texas, USA.
Methods  Species abundance data were compiled for 157 stream fish assemblages in several river basins across Texas. Species were condensed into functional groups based on trophic and life-history characteristics. Local and regional environmental variables were either measured at each location or determined from scale maps and public-access data bases. The original taxonomic and functional group data sets were analysed using similarity indices, null models of co-occurrence, and direct and indirect ordination techniques. Results derived from taxonomic and functional group data sets are compared.
Results  Inferences regarding the relative roles of local and larger-scale factors in determining stream fish assemblage structure differ dramatically between analyses of taxonomic and functional groups. Taxonomic analyses suggest a prominent role of regional-scale environmental factors, and local assemblages sorted according to a biogeographic pattern. Functional group analyses suggest almost equal roles of factors representative of local and larger scales, and assemblages were distinguished by a habitat template irrespective of geographic region.
Main conclusions  The structure of local stream fish assemblages is determined ultimately by factors representing multiple scales, with the relative importance of each depending on the biological unit employed (species or functional groups). We suggest that analyses using functional groups can more directly infer ecological responses to environmental variation, and therefore may provide a more fruitful avenue for developing and testing ecological theory of community organization across biogeographic scales.     

Influence of a cationic detergent on electrophoresis in polyacrylamide gel.

Proteins were subjected to polyacrylamide gel electrophoresis at pH ～ 4 in the presence of the cationic detergent HPCl. The relative electrophoretic mobilities of the proteins were correlated to their molecular weight.     

Chemical modification of carboxyl groups of fibrinogen and its effect on the binding of cationic detergent.

Carboxyl groups of native human fibrinogen were modified with glycine methyl ester and 1-ethyl-3(3-dimethylaminopropyl)carbodiimide. It seemed likely that the modification occurred stepwise. Approximately 26% of the carboxyl groups of fibrinogen was modified finally. The modified fibrinogen had no interaction with cationic detergent, and did not form any complex with the detergent. In dilute acid, fibrinogen was observed to show only a slight interaction with cationic detergent. It is probable that the exposed and ionized carboxyl groups are essential for the formation of a complex between fibrinogen and cationic detergent.     

Influence of macroalgal morphology on the functional structure of molluscan community from hypersaline estuary

Hydrobiologia - Studies based on functional approach seek to understand the ecological roles developed by species as well as their interactions with the environment in which they are inserted. The...