title: Sequence, expression and modeled structure of an aspartic proteinase from the human malaria parasite Plasmodium falciparum.
abstract: A clone encoding the aspartic proteinase (PFAPD) from Plasmodium falciparum strain HB3 was obtained during the course of a project designed to sequence and identify the protein coding regions of the parasite's genome. The protein encoded by the clone contains a sequence identical to the N-terminal sequence determined for an aspartic proteinase isolated from the digestive vacuole of P. falciparum and demonstrated to participate in the hemoglobin digestive pathway (D. Goldberg, personal communication). The translated polypeptide sequence encompasses a number of features characteristic of aspartic proteinases, having > 30% identity and > 50% similarity overall to human cathepsin D, cathepsin E and renin. A model of the three-dimensional structure of PFAPD was constructed using rule-based procedures. This confirms that the primary sequence may be folded as a single chain into a three dimensional structure closely resembling those of other known aspartic proteinases. It includes a lengthy prosegment, two typical-hydrophobic-hydrophobic-Asp-Thr/Ser-Gly motifs and a tyrosine residue positioned in a beta-hairpin loop. The distribution of hydrophobic residues throughout the active site cleft is indicative of a likely preference for hydrophobic polypeptide substrates. The recombinant form of this enzyme expressed using the pGEX2T vector in Escherichia coli is active in digesting hemoglobin at acidic pH and in hydrolyzing a synthetic peptide corresponding to the putative initial cleavage site in hemoglobin. Activity is inhibited completely by pepstatin, confirming the identity of PFAPD as a member of the aspartic proteinase family. Specific mRNA for PFAPD is expressed in the erythrocytic stages of the life cycle.
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Florida, Gainesville 32611.
authors.forename: J B
authors.initials: JB
authors.lastname: Dame
authors.forename: G R
authors.initials: GR
authors.lastname: Reddy
authors.forename: C A
authors.initials: CA
authors.lastname: Yowell
authors.forename: B M
authors.initials: BM
authors.lastname: Dunn
authors.forename: J
authors.initials: J
authors.lastname: Kay
authors.forename: C
authors.initials: C
authors.lastname: Berry
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D016054:DNA, Protozoan / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D017125:Genes, Protozoan; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics*; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D016054:DNA, Protozoan; D016282:Aspartic Acid Endopeptidases