The conformation of polypeptides containing alternating L- and D-amino acids

Delivery of Small Molecules by Syndiotactic Peptides for Breast Cancer Therapy

The utilization of peptide-based drug delivery systems has been suboptimal due to their poor proteolytic susceptibility, poor cell permeability, and limited tumor homing capabilities. Earlier attempts in using d-enantiomers in peptide sequences increased proteolytic stability but have compromised the overall penetration capability. We designed a series of peptides (STRAPs) with a syndiotactic polypeptide backbone that can potentially form a spatial array of cationic groups, an important feature that facilitates cellular uptake. The peptides penetrate cell membranes through a combination of active and passive modes. Furthermore, the cellular uptake of the peptides was unaffected by the presence of or treatment with bovine serum and human plasma. The designed peptides successfully delivered methotrexate, an anticancer drug, to the in vitro and in vivo models of breast cancer, with the best performing peptide STRAP-4-MTX conjugate having an EC50 value of 1.34 μM. Peptide drug delivery in mouse xenograft models showed a greater reduction of primary tumor and metastasis of breast cancer, in comparison to methotrexate of the same dose. The in vivo biodistribution assay of the STRAP-4 peptide suggests that the peptide accumulates at the tumor site after 2 h of treatment, and in the absence of tumors, the peptide gets metabolized and excreted from the system.

Conformational study of linear alternating and mixed D- and L-proline oligomers using electronic and vibrational CD and Fourier transform IR

Vibrational CD (VCD) spectra of a series of blocked linear, alternating D- and L-proline containing oligopeptides, dissolved in D2O and in CDCl3, are reported. For the Boc-LDL-Pro3 to Boc-DLDLDLDL-Pro8 oligomers, the VCD spectra in the amide I band is a positive couplet, opposite in sense to that obtained for (L-Pro)n oligomers. While this admits the possibility of their favoring a right-handed helical chain conformation, the amide I ir spectra for these DL oligomers in D2O indicate a mixed, apparently alternate, cis-trans conformation that prevents a simple conclusion. Their VCD in D2O evidence no narrowing and has a progressive loss in intensity (measured as delta A/A) with an increase in chain length. In CDCl3 a similar pattern of positive VCD couplets decreasing in intensity with length was seen, but the ir spectra are narrower. Their electronic CD (ECD), in the uv, also indicates a loss in intensity with increasing length. Oligomers with odd or even numbers of Pro residues have different ECD patterns, indicating that those spectra are strongly influenced by local contributions arising in the N-terminal groups. The VCD arises from dipolar and vibrational coupling of the amides in the helical structure. All the spectra are consistent with the chiral end groups leading to formation of an excess of one helical handedness. With an increase in length, the influence of this selectiveness is less and the overall CD measured decreases.

Vibrational analysis of the structure of gramicidin A. II. Vibrational spectra

Raman and infrared spectra have been obtained of gramicidin A (GA) in the crystalline state both in the native form and complexed with CsSCN and KSCN, in solution in dioxane, and incorporated into lipid vesicles. Based on predictions from normal mode calculations of a number of relevant single- and double-stranded beta-helix conformations (Naik and Krimm, 1986), it has been possible to assign the structures of GA that are present under the above conditions. In the crystalline state, native GA has a double-stranded increases decreases beta 5.6 structure, whereas complexes with CsSCN or KSCN adopt a increases decreases beta 7.2 structure. In dioxane solution, the increases decreases beta 5.6 structure predominates. In lipid vesicles, the single-stranded beta 6.3-helix is found, which converts to a double-stranded helix on drying the sample. These results support our previous studies in showing that normal mode analysis can be a powerful technique in obtaining three-dimensional structural information from vibrational spectra.

A hypothesis on the role of pressure in the origin of life

The necessity for long time spans in models on the origin of life leads to a major difficulty in that under the environmental conditions existing today biological macromolecules are inherently unstable. The present hypothesis suggests that life arose under a set of environmental conditions whereby polymerization was thermodynamically favored. In particular, increased pressure when coupled with low water activity and high temperature should stabilize polymer bond formation. Three implications of this pressure stabilization theory are presented: (1) The necessary conditions for stabilization are similar to some of the ecological niches occupied by representatives of the archaebacteria. It is suggested that the harsh and unusual habitats of the archaebacteria reflect in part prebiotic environmental conditions. (2) Biological optical activity would be generated if, for instance, L-L peptide bonds were stabilized to a greater degree than L-D peptide bonds. This type of selective stabilization would provide for the maintenance of molecular asymmetry as well as the creation of molecular asymmetry. (3) Conditions necessary for generating the requisite pressure may concurrently have provided protection from prebiotic ultraviolet radiation.

Ion interactions in (1-13C)D-Val8 and D-Leu14 analogs of gramicidin A, the helix sense of the channel and location of ion binding sites

Ion-induced chemical shifts in the carbonyl carbon resonances of synthesized ad verified (1-13C)D-Val8 gramicidin A and (1-13C)D-Leu14 gramicidin A are utilized in combination with the previously determined location of the ion binding sites of the gramicidin A channel (using the carbonyls of L-residues) to determine that the helix sense of the gramicidin A channel) is left-handed. Having resolved the handedness issue, the location of the ion binding sites (which are fundamental to understanding the mechanism of ion transport) are further delineated with the results indicating two sites separated by just over 20 A. Furthermore, the demonstration that the divalent barium ion interacts at the binding site while not being transported through the channel is used to argue that the mechanism of monovalent vs. divalent cation selectivity is due to the positive image force contribution to the central barrier.

Reverse turns in peptides and proteins

The evidence that reverse turns frequently occur as structural components of proteins, as well as of linear and cyclic peptides, is overwhelming. This review summarizes and examines critically the experimental evidence derived from physical methods such as 1H and 13C nuclear magnetic resonance spectroscopy, spin-lattice relaxation time, circular dichroism, IR spectroscopy, and X-ray crystallography. Secondly, theoretical evidence obtained from energy calculations, which rely on empirical energy functions, and correlative methods, which rely on algorithms based on the frequency of occurrence of amino acids, is evaluated. In particular, those theoretical studies for which complementary physical studies have been completed are emphasized. Finally, examples of structure-function relationships involving reverse turns and their biological recognition are demonstrated.