Intracellular fates of cell-penetrating block copolypeptide vesicles

The block copolypeptide poly(l-homoarginine)(60)-b-poly(l-leucine)(20) (R(60)L(20)) was previously found to self-assemble into versatile vesicles with controllable size and encapsulate hydrophilic cargo. These R(60)L(20) vesicles also demonstrated the ability to cross the cell membrane and transport encapsulated cargo into different cell lines. To assess the potential for using the R(60)L(20) vesicles as drug delivery vehicles further, we have investigated their endocytosis and intracellular trafficking behavior. Using drugs that inhibit different endocytosis pathways, we identified macropinocytosis to be a major process by which the R(60)L(20) vesicles enter HeLa cells. Subsequent immunostaining experiments demonstrated that the vesicles entered the early endosomes but not the lysosomes, suggesting that they recycle back to the cell surface. Overall, our studies indicate that the R(60)L(20) vesicles are able to enter cells intact with their cargos, and although some manage to escape from early endosomes, most are trapped within these intracellular compartments.     

Stimuli-responsive zwitterionic block copolypeptides: poly(N-isopropylacrylamide)-block-poly(lysine-co-glutamic acid)

Synthesis of novel zwitterionic block copolypeptides, poly(N-isopropylacrylamide)-block-poly(L-glutamic acid-co-L-lysine) [PNiPAM(n)(PLG(x)-co-PLLys(y))m , where n is the number-average degree of polymerization (DP(n)) of PNiPAM block, x and y are the mole fraction of glutamic acid and lysine residues, respectively, and m is the total DP(n) of the peptide block], and their stimuli-responsiveness to temperature and pH variation in aqueous solutions are described. Initiated with the amino-terminated poly(N-isopropylacrylamide) (PNiPAM(n)-NH2), ring-opening polymerization (ROP) of a mixture of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA), and Boc-L-lysine N-carboxyanhydride (BLLys-NCA) afforded the block copolypeptides PNiPAM(n)(PBLG(x)-co-PBLLys(y))m, with a poly(N-isopropylacrylamide) block together with a random copolypeptide block, which was then deprotected with HBr/trifluoroacetic acid into the double hydrophilic block copolypeptides, PNiPAM(n)(PLG(x)-co-PLLys(y))m. Their block ratios and lengths, as well as the amino acid residue ratios in the random copolypeptide block are varied (n = 360, x = 0.4-0.5, y = 0.4-0.6, and m = 220-252). The secondary structures of the copolypeptides in aqueous solution at different pH conditions were examined. Phase transitions in aqueous solutions induced by both pH and temperature variation were investigated by (1)H NMR spectroscopy. The transitions induced by temperature were also explored by turbidity measurements using UV/vis spectroscopy for their lower critical aggregation temperature (LCAT) determination. Furthermore, these aggregation processes were followed by dynamic light scattering measurements.     

Tuning of collagen triple-helix stability in recombinant telechelic polymers

The melting properties of various triblock copolymers with random coil middle blocks (100-800 amino acids) and triple helix-forming (Pro-Gly-Pro)(n) end blocks (n = 6-16) were compared. These gelatin-like molecules were produced as secreted proteins by recombinant yeast. The investigated series shows that the melting temperature (T(m)) can be genetically engineered to specific values within a very wide range by varying the length of the end block. Elongation of the end blocks also increased the stability of the helices under mechanical stress. The length-dependent melting free energy and T(m) of the (Pro-Gly-Pro)(n) helix appear to be comparable for these telechelic polymers and for free (Pro-Gly-Pro)(n) peptides. Accordingly, the T(m) of the polymers appeared to be tunable independently of the nature of the investigated non-cross-linking middle blocks. The flexibility of design and the amounts in which these nonanimal biopolymers can be produced (g/L range) create many possibilities for eventual medical application.     

Stabilization of Peptide-Based Vesicles via in situ Oxygen-Mediated Cross-Linking

Reversible vesicles from poly(L-glutamic acid)(65) -block-poly[(L-lysine)-ran-(L-3,4-dihydroxyphenylalanine)](75) [PLGA(65) -b-P(LL-r-DOPA)(75) ] block copolypeptide adopt different configurations depending on the surrounding pH. At pH?=?3, AFM and TEM images show ellipsoidal morphologies, whereas at pH?=?12 both TEM and AFM reveal the formation of hollow vesicles. At pH?=?12, the P(LL-r-DOPA) block forms the internal layer of the vesicle shell and the subsequent oxygen-mediated oxidation of the phenolic groups of the DOPA lead to the formation of quinonic intermediates, which undergo intermolecular dimerization to stabilize the vesicles via in situ cross-linking. Consequently, the vesicles maintain their shape even when the pH is reversed back to 3, as confirmed by AFM and TEM.     

Arginine 91 is not essential for flavin incorporation in hepatic cytochrome b(5) reductase

Cytochrome b(5) reductase (cb5r) catalyzes the transfer of reducing equivalents from NADH to cytochrome b(5). Utilizing an efficient heterologous expression system that produces a histidine-tagged form of the hydrophilic, diaphorase domain of the enzyme, site-directed mutagenesis has been used to generate cb5r mutants with substitutions at position 91 in the primary sequence. Arginine 91 is an important residue in binding the FAD prosthetic group and part of a conserved "RxY(T)(S)xx(S)(N)" sequence motif that is omnipresent in the "ferredoxin:NADP(+) reductase" family of flavoproteins. Arginine 91 was replaced with K, L, A, P, D, Q, and H residues, respectively, and all the mutant proteins purified to homogeneity. Individual mutants were expressed with variable efficiency and all exhibited molecular masses of approximately 32 kDa. With the exception of R91H, all the mutants retained visible absorption spectra typical of a flavoprotein, the former being produced as an apoprotein. Visible absorption spectra of R91A, L, and P were red shifted with maxima at 458 nm, while CD spectra indicated an altered FAD environment for all the mutants except R91K. Fluorescence spectra showed a reduced degree of intrinsic flavin fluorescence quenching for the R91K, A, and P, mutants, while thermal stability studies suggested all the mutants, except R91K, were somewhat less stable than the wild-type domain. Initial-rate kinetic measurements demonstrated that the mutants exhibited decreased NADH:ferricyanide reductase activity with the R91P mutant retaining the lowest activity, corresponding to a k(cat) of 283 s(-1) and a K(NADH)(m) of 105 microM, when compared to the wild-type domain (k(cat) = 800 s(-1) K(NADH)(m) = 6 microM). These results demonstrate that R91 is not essential for FAD binding in cb5r; however, mutation of R91 perturbs the flavin environment and alters both diaphorase substrate recognition and utilization.     

A linear correlation between the energetics of allosteric communication and protein flexibility in the Escherichia coli cyclic AMP receptor protein revealed by mutation-induced changes in compressibility and amide hydrogen-deuterium exchange

Amino acid substitutions at distant sites in the Escherichia coli cyclic AMP receptor protein (CRP) have been shown to affect both the nature and magnitude of the energetics of cooperativity of cAMP binding, ranging from negative to positive. In addition, the binding to DNA is concomitantly affected. To correlate the effects of amino acid substitutions on the functional energetics and global structural properties in CRP, the partial specific volume (v(o)), the coefficient of adiabatic compressibility (beta(s)(o)), and the rate of amide proton exchange were determined for the wild-type and eight mutant CRPs (K52N, D53H, S62F, T127L, G141Q, L148R, H159L, and K52N/H159L) by using sound velocity, density measurements, and hydrogen-deuterium exchange as monitored by Fourier transform infrared spectroscopy at 25 degrees C. These mutations induced large changes in v(o) (0.747-0.756 mL/g) and beta(s)(o) (6.89-9.68 Mbar(-1)) compared to the corresponding values for wild-type CRP (v(o)= 0.750 mL/g and beta(s)(o)= 7.98 Mbar(-1)). These changes in global structural properties correlated with the rate of amide proton exchange. A linear correlation was established between beta(s)(o) and the energetics of cooperativity of binding of cAMP to the high-affinity sites, regardless of the nature of cooperativity, be it negative or positive. This linear correlation indicates that the nature and magnitude of cooperativity are a continuum. A similar linear correlation was established between compressibility and DNA binding affinity. In addition, linear correlations were also found among the dynamics of CRP and functional energetics. Double mutation (K52N/H159L) at positions 52 and 159, whose alpha-carbons are separated by 34.6 A, showed nonadditive effects on v(o) and beta(s)(o). These results demonstrate that a small alteration in the local structure due to amino acid substitution is dramatically magnified in the overall protein dynamics which plays an important role in modulating the allosteric behavior of CRP.     

Asymmetrical nitrido tc-99m heterocomplexes as potential imaging agents for benzodiazepine receptors

The design, synthesis, and biological evaluation of nitrido technetium-99m complexes for imaging benzodiazepine receptors are described. The design was performed by selecting the precursor biologically active substrate desmethyldiazepam, and the reactive metal-containing fragment [(99m)Tc(N)(PXP)](2+) (PXP = diphosphine ligand) as molecular building-blocks for assembling the structure of the final radiopharmaceuticals through the application of the so-called 'bifunctional' and 'integrated' approaches. This required the synthesis of the ligands H(2)BZ1, H(2)C1, and H(2)C2 (Figures 1 and 2) derived from desmethyldiazepam. In turn, these ligands were reacted with [(99m)Tc(N)(PXP)](2+) to afford the complexes [(99m)Tc(N)(PXP)(L)] (L = BZ1, C1, C2). The chemical nature of the resulting Tc-99m radiopharmaceuticals was investigated using chromatographic methods, and by comparison with the analogous complexes prepared with the long-lived isotope Tc-99g and characterized by spectroscopic and analytical methods. Results showed that the complexes [(99m)Tc(N)(PXP)(L)] are neutral and possess an asymmetrical five-coordinated structure in which two different bidentate ligands, PXP and L, are coordinated to the same Tc[triple bond]N core. With the ligand H(2)BZ1, two isomers were obtained depending on the syn or anti orientation of the pendant benzodiazepine group relative to the Tc[triple bond]N multiple bond. Biodistribution studies of Tc-99m complexes were carried out in rats, and affinity for benzodiazepine receptors was assessed through in vitro binding experiments on isolated rat's cerebral membranes using the corresponding Tc-99g complexes.     

Architecturally induced multiresponsive vesicles from well-defined polypeptides: formation of gene vehicles

A series of novel, partially labeled amphiphilic triblock copolypeptides, PLL-b-PBLG-d7-b-PLL, has been synthesized, where PLL and PBLG-d7 are poly(L-lysine hydrochloride) and poly(gamma-benzyl-d7-L-glutamate), respectively. The synthetic approach involved the sequential ring-opening polymerization (ROP) of gamma-benzyl-L-glutamate and epsilon-Boc-L-lysine N-carboxy anhydrides by a diamino initiator using high-vacuum techniques, followed by the selective deprotection of the Boc groups. Combined characterization results showed that the copolypeptides exhibit high degrees of molecular and compositional homogeneity. The synthesized copolypeptides had similar molecular weights, while the composition of the middle block ranged between 19 and 74% with respect to the monomeric units. Due to the macromolecular architecture of the copolypeptide and the rigid nature of the middle block, the formation of monolayers was favored, and, surprisingly, vesicles were formed in water at neutral pH over the entire compositional range. The vesicular structures were extensively characterized by static and dynamic light scattering, small-angle neutron scattering, atomic force microscopy, cryo-transmission electron microscopy, scanning electron microscopy, UV and Fourier transform infrared spectroscopy, and circular dichroism. In contrast to other vesicular structures derived from conventional polymers, the formed polypeptidic vesicles possess the unique feature of being stimuli-responsive to pH and temperature. When the copolypeptides were mixed with plasmid DNA (pDNA), large vesicular structures were also formed. The molecular characterization of the vectors was performed with most of the methods mentioned above, and indicated that the pDNA is both partially condensed on the PLL phase and partially encapsulated inside the vesicle. Consequently, the synthesized vectors combine the advantages of the polylysine-DNA systems to condense large amounts of genes, as well as those of the liposome-DNA systems to better protect the encapsulated DNA. These vectors are expected to present better gene transfection efficiency to the cell nucleus.     

Herbicides interacting with lanthanide(III) and calcium(II) ions: structural and biological similarities of Gd and Ca polymers

In this paper we report the synthesis and characterization of Ca(II), Gd(III) and Ce(III) complexes with chlorophenoxyalkanoic acids, which are commonly used as herbicides. The Gd(III) and Ca(II) complexes were characterized by the typical formulas [Gd(III)(L)(3)(H(2)O)(2).2dmf](n) and [Ca(L)(2)(MeOH)(2)](n) [L=[2,4-D=2,4-dichlorophenoxyacetic acid, 2,4,5-T=2,4,5-trichlorophenoxyacetic acid, MCPA=2-methyl-4-chlorophenoxy acetic acid and 2,4-DP=2-(2,4-dichlorophenoxy)propanoic acid]]. The crystal structure of the Gd(III) complex with 2,4-D shows that the compound is a one-dimensional polymer with a [Gd(III)(2)(2,4-D)(6)(H(2)O)(4)] dimeric repeat unit and the gadolinium atoms are in a nine-coordination environment, while the crystal structure of the Ca analog shows that it also has a polymeric structure with a [Ca(2)(2,4-D)(4)(CH(3)OH)(4)] dimeric repeat unit and the calcium atoms are in an eight-coordination environment. The gadolinium compound displays three different coordination modes for the carboxylato moiety, bidentate chelate, bidentate double bound and bidentate triple bound, while the calcium compound displays only one, bidentate triple bound. Coordination spheres are completed with oxygens of H(2)O or MeOH molecules, respectively. The complexes were tested against a few common bacteria by minimum inhibitory concentration (MIC) experiments and did not exhibit any antimicrobial action at concentrations up to 1600 microg/ml.     

Intermolecular interaction and morphology investigation of drug loaded ABA-triblock copolymers with different hydrophilic/lipophilic ratios

Copolymers with different hydrophilic/lipophilic ratios (HLR) were used to optimize the compatibility between polymer as drug carrier and quercetin as lipophilic drug. Synthesis of amphiphilic triblock copolymers (TC) of poly(butylene adipate)–poly(ethylene glycol)–poly(butylene adipate) (PBA–PEG–PBA) with different PBA molecular weights is the first approach for this purpose. Polymerization and structural features of the polymers were analyzed by different characterization techniques (GPC, ¹H NMR and FT-IR). Formation of hydrophobic and hydrophilic domains with different ratios in the ABA-triblock copolymers was studied by ¹H NMR. The sunflower-like nanoparticles were prepared by self-assembling of the amphiphilic copolymers in the aqueous solution. The hydrophobic PBA segments formed the central solid-like core which stabilized by the hydrophilic PEG rings. The optimum HLR for these copolymers was determined on the basis of drug release time and profile, obtained from freeze-dried nanoparticle powders. The results indicated that optimum HLR for the sustained quercetin release obtained at higher molecular weight of polyesteric domains. Zeta potential measurements showed that the nanoparticle size was close related to the initial concentrations of the nanoparticle dispersions and the compositions of the triblock copolymers. Moreover, TEM pictures showed that the nanocarriers morphologies were changed by changing HLR of triblock copolymers. The PBA–PEG–PBA nanoparticles also showed good drug loading properties, suggesting that they were very suitable as delivery devices for hydrophobic drugs.     

Genetic characterization of the (534)DPPR motif of the yeast plasma membrane H(+)-ATPase

The highly conserved motif +(534)DPPR of Saccharomyces cerevisiae H(+)-ATPase, located in the putative ATP binding site, has been mutagenized and the resulting 23 mutant genes conditionally expressed in secretory vesicles. Fourteen mutant ATPases (D534A, D534V, D534L, D534N, D534G, D534T, P535A, P535V, P535L, P535G, P535T, P535E, P535K and R537T) failed to reach the secretory vesicles. Of these mutants, nine (D534N, D534T, P535A, P535V, P535L, P535G, P535T, P535E and P535K) were not detected in total cellular membranes, and five (D534A, D534V, D534G, D534L and R537T) were retained at the endoplasmic reticulum and exhibited a dominant lethal phenotype. The remaining mutants (D534E, R537A, R537V, R537L, R537N, R537G, R537E, R537K and R537H) reached the secretory vesicles at levels similar to that of the wild type. Of these, six (R537A, R537V, R537L, R537N, R537G, and R537E) showed severely decreased ATPase activity compared to the wild type enzyme, and three (D534E, R537K and R537H) rendered an enzyme with an altered K(m) for ATP.     

鹅观草属五个类群的核型与进化

报道了鹅观草属５个类群的核型,即长芒鹅观草,核型２ｎ＝４ｘ＝２８＝２２ｍ＋６ｓｍ（２ＳＡＴ）;短颖鹅观草,核型２ｎ＝４ｘ＝２８＝２０ｍ（２ＳＡＴ）＋８ｓｍ（２ＳＡＴ）;短柄鹅观草,核型２ｎ＝４ｘ＝２８＝２２ｍ（２ＳＡＴ）＋６ｓｍ;纤毛鹅观草,核型２ｎ＝４ｘ＝２８＝２０ｍ＋８ｓｍ（４ＳＡＴ）;毛盘鹅观草,核型２ｎ＝４ｘ＝２８＝１８ｍ＋６ｓｍ（４ＳＡＴ）＋４ｓｔ。同时,通过核型重要性状的递变分析,揭示了鹅观草属５个类群的相对进化程度以及宏观分类中４个组的系统发育关系,表明鹅观草属的半颖组在系统发育中可能既派生了颖体短小的小颖组,又派生了颖体长大的大颖组和长颖组。     

Exciton coupling effects and conformational change of perhexyloligosilanes with optically active methyl(1-naphthyl)phenylsilyl terminals

Perhexyloligosilanes (R,R)-(+)-MeNpPhSi*(Hex(2)Si)(n)Si*PhNpMe (n = 2; (R,R)-(+)-4a, n = 4; (R,R)-(+)-6a, n = 6; (R,R)-(+)-8a) with chiral methyl(1-naphthyl)phenylsilyl terminals were synthesized and characterized. The absorption wavelengths lambda(max) by (1)L(a,Ph) transition of phenyl chromophore conjugated with oligosilane units in (R,R)-(+)-4a - (R,R)-(+)-8a show bathochromic shift of about 3-4 nm compared with those of the alpha,omega-phenyl substituted perhexyloligosilanes Ph(Hex(2)Si)(m)Ph (m = 4; 4b, m = 6; 6b, m = 8; 8b) having the same silicon chain length. Longer chain length induces the separated lambda(max) of (1)L(a,Ph) from (1)B(b,Np) of naphthyl chromophore with positive exciton chiralities. In (R,R)-(+)-8a, although the extremum wavelengths lambda(ext) of exciton coupling between (1)B(b,Np) and (1)L(a,Ph) are separated by about 80 nm, the compound retains the positive exciton chirality, which provides definite information on the absolute configuration of terminal chiral silicon atoms. Bulky terminal substituents and lowering the temperature affect the conformation of the main chain, inducing extended silicon backbone structure.     

Possible implications of serine and tyrosine residues and intermolecular interactions on the appearance of silk I structure of Bombyx mori silk fibroin-derived synthetic peptides: high-resolution 13C cross-polarization/magic-angle spinning NMR study

Bombyx mori silk fibroin molecule is known to exist in two distinct structural forms: silk I (unprocessed silk fibroin) and silk II (processed silk fibroin). Using synthetic peptides, we attempt to explore the structural role played by Ser and Tyr residues on the appearance of silk I structural form of the fibroin. Twelve selected peptides (1-12) incorporating Ser and Tyr residues in the (Ala-Gly)(n) copolypeptide, that is, the sequences mimicking the primary structure of B. mori silk fibroin molecule, have been investigated under the silk I state, employing high-resolution (13)C cross-polarization/magic-angle spinning (CP/MAS) NMR spectroscopy. To acquire the silk I structural form, all the peptides were dissolved in 9 M LiBr and then dialyzed extensively against water, as established previously for the synthetic (Ala-Gly)(15) copolypeptide and B. mori silk fibroin. The diagnostic line shape of the Ala C(beta) peaks and the conformation-dependent (13)C chemical shifts of Ala and Gly resonances are presented to analyze and characterize the structural features. The results indicate that the incorporation of one Ser and/or one Tyr residue(s) at selected position in the basic (Ala-Gly)(15) sequence tend to retain predominantly the silk I structure. Conversely, the repeat pentameric and octameric Ala-Gly-Ser-Gly-Ala-Gly sequences, for example, (Ala-Gly-Ser-Gly-Ala-Gly)(5) or (Ala-Gly-Ser-Gly-Ala-Gly)(8), preferred predominantly the silk II form. The peptide sequences incorporating Ser and Tyr residue(s) into repeat Ala-Gly-Ser-Gly-Ala-Gly sequences, however, adopted the silk II structure with certain content structural heterogeneity or randomness, more pronounced for specific peptides studied. Interestingly, the crystalline Cp fraction of B. mori silk fibroin, when mixed with (Ala-Gly-Ser-Gly-Ala-Gly)(5) sequence in a 5:1 molar ratio, dissolved in 9 M LiBr, and dialyzed against distilled water, favor the silk I form. The finding tends to suggest that the less stable silk I form in (Ala-Gly-Ser-Gly-Ala-Gly)(n) sequences is likely to be induced and facilitated via intermolecular interactions with the Cp fraction, which predominantly prefers the silk I form under similar conditions; however, the hydrogen-bond formation involving O(gamma)H groups of the Ser residues may have some implications.     

Novel peroxidase mimics: mu-Aqua manganese-Schiff base dimers

The interaction of manganese(II) carboxylate salts [Mn(O(2)CR)(2), where R=ethane, pentane] with H(2)L(1) [N,N'-bis(3-methoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] and H(2)L(2) [N,N'-bis(3-ethoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] was studied. MnL(1)(O(2)CEt)(H(2)O) (1), MnL(1)(O(2)CPe(n))(H(2)O) (2), MnL(2)(O(2)CEt)(H(2)O)(2) (3) and MnL(2)(O(2)CPe(n))(H(2)O)(2) (4) were isolated and thoroughly characterised by elemental analysis, FAB mass spectrometry, infrared and (1)H NMR spectroscopy, magnetic susceptibility measurements, molar conductivities, and cyclic and normal pulse voltammetry. Compounds 1 and 2 were crystallographically characterised revealing a tetragonally elongated octahedral geometry for the manganese coordination sphere and also a dimeric nature through mu-aqua bridges. Complexes 1-4 behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS, probably due to their ease to coordinate the substrate molecule. A correlation between rhombicity of the complexes and peroxidase activity has also been established.     

八个四倍体鹅观草属物种的核型研究

对8个鹅观草属物种的核型进行了研究。核型公式如下:纤穗鹅观草2n=4x=28=20m+8sm(2sat);紫穗鹅观草2n=4x=28=22m(2sat)+6sm;假花鳞草2n=4x=28=24m(2sat)+4sm;肃草2n=4x=28=22m+6sm(2sat);小颖鹅观草2n=4x=28=22m+6sm(2sat);纤瘦鹅观草2n=4x=28=24m(4sat)+4sm;变颖鹅观草2n=4x=28=20m+8sm(2sat);毛花鹅观草2n=4x=28=24m(2sat)+4sm。它们的核型属1A或2A型。其中后5个物种的核型为首次报道。     

Detergent-like action of the antibiotic peptide surfactin on lipid membranes

Surfactin is a bacterial lipopeptide with powerful surfactant-like properties. High-sensitivity isothermal titration calorimetry was used to study the self association and membrane partitioning of surfactin. The critical micellar concentration (CMC), was 7.5 microM, the heat of micellization was endothermic with DeltaH(w-->m)(Su) = +4.0 kcal/mol, and the free energy of micellization DeltaG(O,w-->m)(Su) = -9.3 kcal/mol (25 degrees C; 100 mM NaCl; 10 mM TRIS, 1 mM EDTA; pH 8.5). The specific heat capacity of micellization was deduced from temperature dependence of DeltaH(w-->m)(Su) as DeltaC(w-->m)(P) = -250 +/- 10 cal/(mol.K). The data can be explained by combining the hydrophobicity of the fatty acyl chain with that of the hydrophobic amino acids. The membrane partition equilibrium was studied using small (30 nm) and large (100 nm) unilamellar POPC vesicles. At 25 degrees C, the partition coefficient, K, was (2.2 +/- 0.2) x 10(4) M(-1) for large vesicles leading to a free energy of DeltaG(O, w-->b)(Su) = -8.3 kcal/mol. The partition enthalpy was again endothermic, with DeltaH(w-->b)(Su) = 9 +/- 1 kcal/mol. The strong preference of surfactin for micelle formation over membrane insertion explains the high membrane-destabilizing activity of the peptide. For surfactin and a variety of non-ionic detergents, the surfactant-to-lipid ratio, inducing membrane solubilization, R(sat)(b), can be predicted by the simple relationship R(sat)(b) approximately K. CMC.     

Studies on interaction between poly(L-lysine58, L-phenylalanine42) and deoxyribonucleic acids.

A random copolymer of 58% L-lysine and 42% L-phenylalanine, poly(Lys58Phe42), was used as a model protein for studying the role of phenylalanine residues in protein-DNA interaction. Complexes between this copolypeptide and DNA, made by direct mixing, were studied by absorbance, circular dichroism (CD), fluorescence, and thermal denaturation. Complex formation results in an increase in absorbance, and an enhancement, red-shift, and broadening of phenylalanine fluorescence. The fluorescence enhancement is opposite to the quenching observed when a tyrosine copolypeptide is bound to DNA (R. M. Santella and H.J. Li (1974), Biopolymers 13, 1909). The positive CD band of DNA near 275 nm is reduced and red-shifted by the binding of the phenylalanine copolypeptide to a greater extent than by the tyrosine copolypeptide. Thermal denaturation of the complexes in 2.5 times 10(-4) M EDTA (pH 8.0) shows three characteristic melting bands. For complexes with calf thymus DNA, free base pairs melt at Tm,I (47-49 degrees) and copolypeptide-bound base pairs show two melting bands (Tm,II at 73-75 degrees, and Tm,III at 88 -90 degrees). Similar thermal denaturation results have been observed for complexes with Micrococcus luteus DNA. The fluorecence intensity of the complexes is greatly increased when the temperature is raised to the Tm,II region. In addition to fluorescence measurements, the effects of increasing temperature on absorption and CD spectra of the complexes were also studied. Stacking interaction between the phenylalanine chromophore and DNA bases, either partial or full intercalation, is implicated by the experimental results. Several mechanisms are proposed to describe the reaction between the copolypeptide and DNA, and thermal denaturation of the complex.     

Self-assembly of polypeptide-containing ABC-type triblock copolymers in aqueous solution and its pH dependence

Self-assembling of novel biodegradable ABC-type triblock copolymer poly(ethylene glycol)-poly(L-lactide)-poly(L-glutamic acid) (PEG-PLLA-PLGA) is studied. In aqueous media, it self-assembles into a spherical micelle with the hydrophobic PLLA segment in the core and the two hydrophilic segments PEG and PLGA in the shell. With the lengths of PEG and PLLA blocks fixed, the diameter of the micelles depends on the length of the PLGA block and on the volume ratio of H(2)O/dimethylformamide (DMF) in the media. When the PLGA block is long enough, morphology of the self-assembly is pH-dependent. It assembles into the spherical micelle in aqueous media at pH 4.5 and into the connected rod at or below pH 3.2. The critical micelle concentration (cmc) of the copolymer changes accordingly with decreasing solution pH. Both aggregation states can convert to each other at the proper pH value. This reversibility is ascribed to the dissociation and neutralization of the COOH groups in the LGA residues. When the PLGA block is short compared to the PEG or PLLA block, it assembles only into the spherical micelle at various pH values.     

Molecular simulation of self-assembly of hydrophilic functionalized aromatics in aqueous solutions

This study identifies mechanisms of self-assembly of hydrophilic functionalized aromatic molecules—a distinct class of lyotropic materials. Results from molecular dynamics studies used to understand the moieties of the lyotropic molecule that affect the structure are consistent with experimental observations of these self-assembled structures. Coulombic forces, dominated by π–π interactions drives the self-assembly of this class of materials. Intra-molecular configurations of the aromatic rings—the extent of torsion or bending between the rings—as well as the structure of functional groups connected to the rings affect the self-assembled structures. In addition, the chemistry of the functional groups also affects how the molecules are oriented as they self assemble. Molecular modeling provides insight into design of these molecules.