Effects of Helical Sense and Macrodipole on Helix Interaction in Poly(glutamic acid) Monolayers at the Air-Water Interface

Structural analysis of amyloid ? peptide fragment (25-35) in different microenvironments

Amyloid beta (Abeta) peptides are one of the classes of amphiphilic molecules that on dissolution in aqueous solvents undergo interesting conformational transitions. These conformational changes are known to be associated with their neuronal toxicity. The mechanism of structural transition involved in the monomeric Abeta to toxic assemblage is yet to be understood at the molecular level. Early results indicate that oriented molecular crowding has a profound effect on their assemblage formation. In this work, we have studied how different microenvironments affect the conformational transitions of one of the active amyloid beta-peptide fragments (Abeta(25-35)). Spectroscopic techniques such as CD and Fourier transform infrared spectroscopy were used. It was observed that a stored peptide concentrates on dissolution in methanol adopts a minor alpha-helical conformation along with unordered structures. On changing the methanol concentration in the solvated film form, the conformation switches to the antiparallel beta-sheet structure on the hydrophilic surface, whereas the peptide shows transition from a mixture of helix and unordered structure into predominantly a beta-sheet with minor contribution of helix structure on the hydrophobic surface. Our present investigations indicate that the conformations induced by the different surfaces dictate the gross conformational preference of the peptide concentrate.

Solvent Specified Conformation in Poly(α-l-glutamic acid) Thin Films

The ability to control conformational properties of polypeptides in their films is of considerable interest for many possible applications of these materials. By rational choice of the solvent system for film fabrication, control over the conformation of the main chain, the intermolecular hydrogen bonding in the side chain is easily achieved in poly(alpha-L-glutamic acid) (PLGA) thin films. The spectral data from circular dichromism (CD), FT-IR, and solid state (13)C NMR spectroscopies suggest that the beta-sheet conformation is dominant in PLGA films cast from trifluoroacetic acid (TFA) solution, whereas the right-handed alpha-helix is dominant in those cast from pyridine or DMF solution. In comparison with films cast from TFA solutions, the films fabricated from pyridine or DMF solutions exhibit strong intermolecular hydrogen bondings between -COOH groups and have a more ordered arrangement of side chains. Moreover, the extent of alpha-helix conformation of the PLGA backbone in films cast from pyridine or DMF solution is several times higher than that observed in the PLGA powder precipitated from aqueous solution at pH 4. All spectroscopic studies indicate clearly that the solvents (used for casting these films) play a crucial role in directing the organization of PLGA in these thin films.

The merozoite surface protein 6 gene codes for a 36 kDa protein associated with the Plasmodium falciparum merozoite surface protein-1 complex

A complex of non-covalently bound polypeptides is located on the surface of the merozoite form of the human malaria parasite Plasmodium falciparum. Four of these polypeptides are derived by proteolytic processing of the merozoite surface protein 1 (MSP-1) precursor. Two components, a 22 and a 36 kDa polypeptide are not derived from MSP-1. The N-terminal sequence of the 36 kDa polypeptide has been determined, the corresponding gene cloned, and the protein characterised. The 36 kDa protein consists of 211 amino acids and is derived from a larger precursor of 371 amino acids. The precursor merozoite surface protein 6 (MSP-6) has been designated, and the 36 kDa protein, MSP-6(36). Mass spectrometric analysis of peptides released from the polypeptide by tryptic digestion confirmed that the gene identified codes for MSP-6(36). Antibodies were produced to a recombinant protein containing the C-terminal 45 amino acid residues of MSP-6(36). In immunofluorescence studies these antibodies bound to antigen at the parasite surface or in the parasitophorous vacuole within schizonts, with a pattern indistinguishable from that of antibodies to MSP-1. MSP-6(36) was present in the MSP-1 complex immunoprecipitated from the supernatant of in vitro parasite cultures, but was also immunoprecipitated from this supernatant in a form not bound to MSP-1. Examination of the MSP-6 gene in three parasite lines detected no sequence variation. The sequence of MSP-6(36) is related to that of the previously described merozoite surface protein 3 (MSP-3). The MSP-6(36) amino acid sequence has 50% identity and 85% similarity with the C-terminal region of MSP-3. The proteins share a specific sequence pattern (ILGWEFGGG-[AV]-P) and a glutamic acid-rich region. The remainder of MSP-6 and MSP-3 are unrelated, except at the N-terminus. Both MSP-6(36) and MSP-3 are partially associated with the parasite surface and partially released as soluble proteins on merozoite release. MSP-6(36) is a hydrophilic negatively charged polypeptide, but there are two clusters of hydrophobic amino acids at the C-terminus, located in two amphipathic helical structures identified from secondary structure predictions. It was suggested that this 35 residue C-terminal region may be involved in MSP-6(36) binding to MSP-1 or other molecules; alternatively, based on the secondary structure and coil formation predictions, the region may form an intramolecular anti-parallel coiled-coil structure.