Surface chemistry of poly (beta-benzyl L-aspartate)

Effects of ayahuasca on mental health and quality of life in naïve users: A longitudinal and cross-sectional study combination

Ayahuasca is a hallucinogenic decoction used as a traditional medicine in several Amazonian regions. The ritualistic use of ayahuasca has spread throughout many countries, making it necessary to study its risks and benefits. Two sub-studies were designed for this investigation. In sub-study 1, a psychiatric interview and a battery of questionnaires were administered to subjects (n = 40) before their first ayahuasca use. Two follow-ups were conducted at 1 and 6 months. In sub-study 2, the same interview and battery of questionnaires were administered to long-term ayahuasca users (n = 23) and their scores were compared with those of the ayahuasca-naïve group. In the first assessment, nearly half (45%) of the naïve users were found to meet the diagnostic criteria for a psychiatric disorder. After the ayahuasca use, more than 80% of those subjects showed clinical improvements that persisted at 6 months. The questionnaires showed significant reductions in depression and psychopathology. Regarding sub-study 2, long-term users showed lower depression scores, and higher scores for self-transcendence and quality of life, as compared to their peers in sub-study 1. Further controlled and observational naturalistic studies assessing the eventual risks and potential benefits of ayahuasca are warranted.

Nuclear magnetic relaxation dispersion study of the dynamics in solid homopolypeptides

The (1)H nuclear magnetic relaxation dispersion profiles were measured from 10 kHz to 30 MHz as a function of temperature for polyglycine, polyalanine, polyvaline, and polyphenylalanine to examine the contributions of different side chain motions to the polypeptide proton relaxation rate constants. The spin-fracton theory for (1)H relaxation is modified to account for high frequency motions of side chains that are dynamically connected to the linear polymer backbone. The (1)H relaxation is dominated by propagation of rare disturbances along the backbone of the polymer. The side-chain dynamics cause an off-set in the field dependence of the (1)H spin-lattice relaxation rate constants which obey a power law in the Larmor frequency in the limit of low and high magnetic field strength.

A study of conformational stability of poly(L-alanine), poly(L-valine), and poly(L-alanine)/poly(L-valine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR

13C cross-polarization/magic angle spinning (CP/MAS) NMR and (1)H T(1rho) experiments of poly(L-alanine) (PLA), poly(L-valine) (PLV), and PLA/PLV blends have been carried out in order to elucidate the conformational stability of the polypeptides in the solid state. These were prepared by adding a trifluoroacetic acid (TFA) solution of the polymer with a 2.0 wt/wt % of sulfuric acid (H(2)SO(4)) to alkaline water. From these experimental results, it is clarified that the conformations of PLA and PLV in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.

A study of conformational stability of polyglycine and poly(L-alanine), and polyglycine/poly(L-alanine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR

13C Cross-Polarization/Magic Angle Spinning nmr and T(1rhoH) experiments of polyglycine (PG), poly(L-alanine) (PLA), and PG/PLA blends prepared from dichloroacetic acid solution have been carried out, in order to elucidate the conformational stability of these polypeptides in the solid state. From these experimental results, it was clarified that the conformations of PG and PLA in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.

Conformational transitions in model silk peptides

Protein structural transitions and beta-sheet formation are a common problem both in vivo and in vitro and are of critical relevance in disparate areas such as protein processing and beta-amyloid and prion behavior. Silks provide a "databank" of well-characterized polymorphic sequences, acting as a window onto structural transitions. Peptides with conformationally polymorphic silk-like sequences, expected to exhibit an intractable beta-sheet form, were characterized using Fourier transform infrared spectroscopy, circular dichroism, and electron diffraction. Polymorphs resembling the silk I, silk II (beta-sheet), and silk III (threefold polyglycine II-like helix) crystal structures were identified for the peptide fibroin C (GAGAGS repetitive sequence). Two peptides based on silk amorphous sequences, fibroin A (GAGAGY) and fibroin V (GDVGGAGATGGS), crystallized as silk I under most conditions. Methanol treatment of fibroin A resulted in a gradual transition from silk I to silk II, with an intermediate state involving a high proportion of beta-turns. Attenuated total reflectance Fourier transform infrared spectroscopy has been used to observe conformational changes as the peptides adsorb from solution onto a hydrophobic surface. Fibroin C has a beta-strand structure in solution but adopts a silk I-like structure upon adsorption, which when dried on the ZnSe crystal contains silk III crystallites.

Structural study of poly(beta-benzyl-L-aspartate) monolayers at air-liquid interfaces

As normally studied, in the solid state or in solution, poly(beta-benzyl-L-aspartate) (PBLA) differs from the other helical polyamino acids in that its alpha-helical conformation is most stable in the left-handed rather than in the right-handed form. The slightly lower energy per residue for the left-handed form in PBLA is easily perturbed, however. The helical screw sense can be inverted in a polar environment and, upon heating above 100 degrees C, a distorted left-handed helix or omega-helix is irreversibly formed. From external reflectance Fourier transform infrared measurements at the air-water interface, the conformation of PBLA in the monolayer state is directly established for the first time. The infrared frequencies of the amide bands suggest that right-handed alpha-helices are formed on the surface of water immediately after spreading the monolayers and independently of the polypeptide conformational distribution in the spreading solution. The right-handed helical form prevails throughout the slow compression of the Langmuir monolayers to collapsed films. The helical screw sense can be reversed by lowering the polarity of the aqueous phase. In addition, an alternate conformation similar to the omega-helix forms on addition of small amounts of isopropanol to the aqueous subphase, and appears to be an intermediate in the helix-helix transition.

Interaction of Bovine Myelin Basic Protein with Cholesterol

The interaction of myelin basic protein with cholesterol and the conformational changes occurring in the protein upon interaction with the lipid were investigated. The myelin basic protein (MBP) plays an important role in stabilizing the multilamellar structure of the myelin membrane. MBP interacts in a specific way with the lipids components of the membrane. The major lipid component is the cholesterol which comprises 40-44 mol% of the lipids. In order to understand the effect of the lipids in the protein conformation we have studied the interaction between MBP and cholesterol. The conformational changes induced in the protein upon interaction with different concentrations of cholesterol were characterized by transmission electron microscopy (TEM) and monolayer studies. Aqueous solution of MBP from bovine brain (obtained by the method of Cheifetz and Moscarello) exhibited a circular dichroism (CD) spectrum characteristic of random coil protein molecules. Upon addition of cholesterol, MBP-cholesterol complexes were observed by TEM. The monolayer compression experiments show plateaus in their surface pressure-area isotherms. The presence of these plateaus has previously been interpreted as alpha-helix conformation. By seeding the MBP onto the aqueous support, we have determined the compression work for the protein on the surface. Experimental areas of the mixtures MBP-cholesterol are smaller than the area calculated by adding the areas of the pure components, indicating that there are attractive forces between both components. The calculated entropy of compression indicates that the highest organization is reached when lipid and protein are almost in the same proportion. Copyright 1998 Academic Press.

Membrane optical activity: some facts and fallacies

The circular dichroism of hypothetical, water-filled, spherical shells, 75-3500 nm in radius, with walls 7.5 nm thick, composed of poly(L-lysine) in various conformational proportions, and suspended in water, were computed from the known optical properties of this polypeptide by classical general light-scattering theory (Mie theory). Comparison of the computed curves of circular dichroism spectra with those of diverse membranes reveals large discrepancies below 215 nm and shows that light scattering does not adequately account for the optical activity of membranes containing appreciable proportions of nonhelical conformation. However, turbidity effects can explain the anomalies of membrane optical rotatory dispersion near 233 nm, if not uniquely so. We conclude that the optical activity of neither most soluble proteins nor membrane proteins can provide accurate conformational information when synthetic polypeptides are used as standards and list the reasons for this argument. We also show that present techniques to "correct" membrane optical activity are likely to produce additional artifact.