Primary and predicted secondary structures of the caseins in relation to their biological functions

In free solution, the caseins behave as non-compact and largely flexible molecules with a high proportion of residues accessible to solvent. Historically, they have been described as random coil-type proteins with only a nutritional function. Nevertheless, secondary structure prediction algorithms indicate that many parts of the (unphosphorylated, unglycosylated) polypeptide chains can form regular structures. In particular, a recurrent motif of the Ca2+-sensitive caseins in man, rat, mouse, guinea pig and ruminant species is an alpha-helix--loop--alpha-helix conformation in which the loop region typically contains a cluster of sites of phosphorylation. The biological function of the caseins is considered and it is suggested that the potential or actual conformations of the group of Ca2+-sensitive caseins are suited to the function of modulating the precipitation of calcium phosphate from solution. Either they can act as sites for nucleation or they can bind rapidly to calcium phosphate nuclei as they form spontaneously from supersaturated solution.     

Nucleotide-amino acid interactions and their relation to the genetic code

Summary The apparent dissociation constants of the complexes of AMP with the methyl esters of amino acids in aqueous solution exhibit good correlations with features of the genetic code and with the frequencies of occurrence of amino acid residues in proteins. Thus it is likely that chemically selective nucleotide-amino acid interactions were involved in the processes of chemical evolution that have led to the emergence of the genetic code. Based on these correlations a storage device for the information regarding nucleotide-amino acid interactions is proposed. It involves processes of simultaneous polymerization to polynucleotides and polypeptides.     

Assemblies of psoriatic keratin and their relation to normal intermediate filament structures

Protein extracts from normal human epidermis reassemble in vitro into 8-10 nm diameter filaments characteristic of intermediate filaments, whereas extracts from psoriatic epidermal scales reassemble, under identical conditions, into a variety of paracrystalline bundles. Optical diffraction and image analysis of these paracrystalline bundles reveal an axial repeat of 16.5 nm, which subdivides into three bands of 5.5 nm, and a lateral spacing of 5.1 nm. This information, together with available sequence studies of intermediate filaments and biochemical data, suggests that the subunit of psoriatic keratin is made up essentially from the coiled-coil alpha-helical rod domain of the normal keratin subunits, whereas the random coil domains are missing or greatly reduced in size.     

Plant growth-promoting activities of alkoxycarbonylisoureas in relation to their chemical structures

A number of alkoxycarbonylisourea derivatives were synthesized and their plant growth-promoting activities examined by the rice (Oryza sativa) seedling test. Isourea compounds with an appropriate substituent such as a halogen atom or a methyl, ethyl or methoxy group at the para-position on a benzene ring in 1-alkoxycarbonyl-2-alkyl-3-phenylcarbamoylisoureas promoted the growth of rice seedlings and acted as a highly active gibberellic acid-synergist when used in combination with gibberellic acid. The common structural requirements of isourea derivatives applied well for a growth promoter and a gibberellic acid-synergist.     

Histone H1-DNA interactions and their relation to chromatin structure and function

The belief that histone H1 interacts primarily with DNA in chromatin and much less with the protein component has led to numerous studies of artificial H1-DNA complexes. This review summarizes and discusses the data on different aspects of the interaction between the linker histone and naked DNA, including cooperativity of binding, preference for supercoiled DNA, selectivity with respect to base composition and nucleotide sequence, and effect of H1 binding on the conformation of the underlying DNA. The nature of the interaction, the structure of the complexes, and the role histone H1 exerts in chromatin are also discussed.     

Engineering of caseins and modulation of their structures and interactions

β-Casein (β-CN) is a milk protein widely used in food industries because of its mild emulsifying properties due to its amphiphilicity. However, the elements determining its micellization behavior in solution and interfacial behavior at the air–water interface are not well known. In order to study how the forced dimerisation influences functional properties of β-CN, recombinant wild-type β-CN was produced and distal cysteinylated forms of recombinant β-CN were engineered. We show that 1) cysteinylated β-CN formed mainly dimers bridged by disulfide bonds; 2) the process of dimerization adds to the micellization process with temperature and is poorly reversible; 3) covalent disulfide linkage forms at the air–water interface at a lower temperature than in bulk. In conclusion, the location of the cysteinylation in the C-terminus or N-terminus or both is of importance for the properties of β-CN.     

The stability of host-pathogen interactions of plant disease in relation to biological weed control

A theoretical analysis was conducted to investigate the dynamics of plant-pathogen interactions for biological weed control. Computer simulation showed that the dynamics of plant-pathogen interactions can be determined by the properties of the pathogen. Pathogens with high levels of virulence may exist in nature in low frequencies due to high extinction rates. Pathogens of this type are suitable for the mycoherbicide strategy. Pathogens with a low level of virulence are frequent and may coexist stably with their host. Good candidates for the classical strategy may be the pathogens with intermediate pathogenicity, which maintain a stable interaction and a high control efficiency. The probability of extinction of a pathogen increases when pathogenicity is greater than a critical value at the intermediate range. The regulation of plant populations through reducing host reproductivity and increasing host mortality has similar results.     

Electrodynamics of interactions in electrolyte solutions and their biological significance

Attention is drawn to the fact that the interaction of charges in aqueous solutions of electrolytes, such as media having physiological characteristics, depends not only on the distance between interacting charges but also on the frequency that determines their dynamics. This fact has significant consequences for some biological processes and their kinetics. The analysis of reasons for charge shielding, including the dynamic effects, shows that, even at distances exceeding the Debye length, electric interactions in systems similar to physiological are effective provided that charges move with frequencies higher than 250 MHz. For each electrolyte solution, the threshold frequency (Maxwell frequency) can be found, which determines the transition from the conducting to the dielectric mode of interactions of charges in physiological solutions.     

Structural elements of human parathyroid hormone and their possible relation to biological activities.

Human parathyroid hormone (hPTH) and several deletion analogues were examined for the presence of secondary structure using circular dichroism spectroscopy. The spectra of hPTH and the deletion analogues 8-84, 34-53, 53-84, 1-34, 13-34, 1-19, and 20-34, in neutral, aqueous buffer, gave no evidence for extensive secondary structure. An alpha-helical-like spectral contribution was found to arise from a region within peptide 13-34. This spectral contribution was speculated to arise from partial stability of a helix consisting of residues 17-29. Molecular dynamics simulations of peptide 1-34 suggested that this peptide tends to fold with a bend defined by residues 10-14, with the amino-terminal and carboxyl-terminal residues tending to be in more extended forms and the other residues in helical-like conformations. The addition of trifluoroethanol promoted the formation of alpha-helix, mainly in the 1-34 region. The putative helix comprised of residues 17-29 was stabilized by the addition of 10-20% TFE, while a second putative helix proximal to the amino terminus, and comprised of residues 3-11, was stabilized by slightly higher concentrations of TFE. An amphiphilic sequence was identified within the 20-34 fragment. The development of alpha-helix on binding this fragment, and other analogues containing this sequence, to palmitoyloleoylphosphatidylserine vesicles provided experimental evidence for the potential role of this amphiphilic sequence in binding to membranes or to a membrane receptor. The relationships between these alpha-helical regions in 1-34, either potentiated by trifluoroethanol or lipid vesicles, are discussed in terms of different receptor-binding regions within hPTH.     

Chemical constituents from Oncocalyx glabratus and their biological activities

Chemical investigation of the aerial parts of Oncocalyx glabratus resulted in the isolation of three new flavan derivatives, 5,3′,4′-trihydroxyflavan 7-O-gallate (1), 5,4′-dihydroxyflavan 7-3′-O-digallate (2) and 5,3′-dihydroxyflavan 7-4′-O-digallate (3), named oncoglabrinol A, B and C, respectively, together with four known flavonols, (+)-catechin (4), (+)-catechin-7-O-gallate (5), catechin-7-4′-O-digallate (6A) and catechin-7-3′-O-digallate (6B). The structures of the compounds were established by 1D, 2D NMR and ESI-HRMS spectral analyses. The biological activity of the compounds was tested through a series of in vitro assays designed for determining cytotoxicity, antiviral activity against hepatitis B virus, and antidiabetic activity. All compounds were found non-toxic and showed moderate anti-HBV activity. Compounds 3 and 6 showed dual PPAR agonistic activity while others were not effective.     

Progress in designing nucleic acid structures and fine-tuning their interactions

The prediction of the structure of biological macromolecules at the atomic level and the design of new meta-stable structures and secondary interactions are critical tests of our understanding of the structures and the inter-atomic forces that underlie molecular biology. The capacity to accurately predict and design new structures and interactions will allow us to create nucleic acid sequences that will fold in new and useful ways. Here, we present some results to demonstrate the progress we have made in designing and assembling new nucleic acid structures that will make an increasingly important contribution to biology and medicine. We call the reaction cycle that exemplifies our approach 'A handshake from a hairpin on the way to a double helix.'     

Total synthesis of chain-length-uniform dolichyl phosphates and their fitness to accept hexoses in the enzymatic formation of lipoglycans

Dolichols of defined uniform chain length (C35, C45, and C55) and geometry were prepared by total synthesis according to the following principle: (E,E)-Farnesol, activated as its 4-tolyl sulfone, is condensed with 8-chloroneryl benzyl ether, the sulfonyl group removed and the ether linkage cleaved by lithium/triethylamine. The resulting elongated prenol is converted again to its corresponding 4-toly/sulfone; at this stage isomers are removed by chromatography. After several cycles of this C10-elongation sequence the synthesis is completed in the same way but using 8-chlorocitronellyl benzyl ether as building block to introduce the saturated alpha-isoprene unit. The dolichols obtained were chemically phosphorylated (POCl3/Et3N). Both, the alcohols and their phosphate esters, are characterized spectroscopically. 1H- and 13C-NMR data are recorded for qualitative and stereochemical comparison with natural dolichols. The authentic dolichyl phosphates (Dol-7-P, Dol-9-P, and Dol-11-P) were assayed relative to the natural dolichyl phosphate mixture from pig liver as acceptors for transglycosylation from nucleoside diphosphate sugars (glucose, mannose) by standardized membrane vesicle preparations from plants (Volvox) and animals (liver). Even the shortest chain dolichyl 7-phosphate has full activity in this lipoglycan-forming reaction.     

Bird-plant interactions and vulnerability to biological invasions

Aims Species interactions regulate the invasiveness of non-native species and as declines of native tree species escalate, exotic tree species that offer supplementary resources to animal seed-dispersers should expand their distributions as they fill ecological roles. Our primary objective was to forecast impacts from an imminent biological invasion (laurel wilt disease) by quantifying resources provided by native (threatened) and exotic fruits (disease-resistant) and associated bird foraging preferences.Methods In the southeastern USA, we tested for redundancy among the resources provided by native and exotic fruits to overwintering birds. Comparisons between abundant subcanopy species Persea borbonia (native) and Cinnamomum camphora (exotic) were paramount considering the widespread disease-induced decline of P. borbonia, and the biological and phylogenetic similarities between these species. Across two winter survey periods, we quantified fruit removal and documented bird species using motion-activated cameras in the field. Physical and chemical fruit characteristics were also quantified.Important findings Foraging bouts on both P. borbonia and C. camphora fruits were documented for four native bird species. There was no difference in selectivity between fruit types during Year 1 of our survey, but there was a significant preference for C. camphora fruit in Year 2; the change in preference was correlated with significantly lower temperatures in Year 2. While the pulp/seed ratio and moisture content differed, the nutritional content of fruit pulp (g/100g) was similar between fruit types. Given the apparent redundancy among these native and exotic fruit resources, we forecast increases in the consumption and dispersal of exotic propagules following the widespread laurel wilt disease-induced decline of P. borbonia and other native fruit bearing members of Lauraceae. This empirically based prediction is among the first to document exotic forest pathogens as indirect threats to native bird–plant interactions and potential facilitators of exotic plant invasion.