SOLUTION STRUCTURE OF A POLYPEPTIDE CONTAINING 4 HEPTAD REPEAT UNITS FROM A MEROZOITE SURFACE-ANTIGEN OF PLASMODIUM-FALCIPARUM

MULHERN, TD; Howlett, GJ; Reid, GE; Simpson, RJ; McColl, DJ; Anders, RF; Norton, RS

Author(s): MULHERN, TD; Howlett, GJ; Reid, GE; Simpson, RJ; McColl, DJ; Anders, RF; Norton, RS;
Details: Publication Year 1995-03-21,Volume 34,Issue #11,Page 3479-3491
Journal Title: BIOCHEMISTRY
Publication Type: Journal Article
Abstract: The Plasmodium falciparum antigen SPAM (secreted polymorphic antigen associated with merozoites) contains an unusual set of heptad repeat units with alanine at the a and d positions. Twelve heptads with the consensus sequence AXXAXXX occur in three blocks of four, linked by short nonrepetitive sequences. A 38-residue polypeptide comprising the first block of four heptad units and five flanking residues at either end, SPAM-H1, has been synthesized and its structure in aqueous solution determined from H-1 NMR data. Sedimentation equilibrium showed the peptide to be monomeric in aqueous solution. Its structure was determined from H-1 NMR-derived distance and dihedral angle constraints by using distance geometry calculations, restrained simulated annealing, and conjugate gradient energy minimization in the CHARMm force field. The polypeptide contains an alpha-helix extending from Ser10 (position e of the first heptad) to at least Lys32 (position f of the fourth heptad) and possibly as far as Val35. The helix is bent, partly as result of a kink around residues 19-20. The conformations of the nine N-terminal residues and the six C-terminal residues are not well defined by the NMR data. The rms deviation from the average of the 20 best structures over the well-defined region (residues 11-31, which have backbone angular order parameters > 0.8) was 1.56 Angstrom for backbone heavy atoms (N, C-alpha, and C) and 2.12 Angstrom for all heavy atoms. (H2O)-H-2 exchange experiments identified slowly exchanging amide protons near the C-terminus and the last two turns of the helix. The unusual stability of the C-terminus reflects the presence of a new C-capping motif, which may involve the side chain of an asparagine in a position external to the C-cap residue. Possible interactions of the H1 sequence with the other two heptad repeat units in the intact merozoite antigen are discussed.
Publisher: AMER CHEMICAL SOC
Keywords: NUCLEAR-MAGNETIC-RESONANCE; SPIN COUPLING-CONSTANTS; GCN4 LEUCINE-ZIPPER; PROTEIN SECONDARY STRUCTURE; ALPHA-HELICES; COILED COILS; AMINO-ACIDS; ERYTHROCYTIC STAGES; CHEMICAL-SHIFTS; SPECTROSCOPY
Publisher's Version: https://doi.org/10.1021/bi00011a001
Terms of Use/Rights Notice: Refer to copyright notice on published article.

Creation Date: 1995-03-21 12:00:00