title: Computational reverse-engineering of a spider-venom derived peptide active against Plasmodium falciparum SUB1.
abstract: BACKGROUND
  Psalmopeotoxin I (PcFK1), a protein of 33 aminoacids derived from the venom of the spider Psalmopoeus Cambridgei, is able to inhibit the growth of Plasmodium falciparum malaria parasites with an IC50 in the low micromolar range. PcFK1 was proposed to act as an ion channel inhibitor, although experimental validation of this mechanism is lacking. The surface loops of PcFK1 have some sequence similarity with the parasite protein sequences cleaved by PfSUB1, a subtilisin-like protease essential for egress of Plasmodium falciparum merozoites and invasion into erythrocytes. As PfSUB1 has emerged as an interesting drug target, we explored the hypothesis that PcFK1 targeted PfSUB1 enzymatic activity.
  
  
  RESULTS
  Molecular modeling and docking calculations showed that one loop could interact with the binding site of PfSUB1. The calculated free energy of binding averaged -5.01 kcal/mol, corresponding to a predicted low-medium micromolar constant of inhibition. PcFK1 inhibited the enzymatic activity of the recombinant PfSUB1 enzyme and the in vitro P. falciparum culture in a range compatible with our bioinformatics analysis. Using contact analysis and free energy decomposition we propose that residues A14 and Q15 are important in the interaction with PfSUB1.
  
  
  CONCLUSIONS
  Our computational reverse engineering supported the hypothesis that PcFK1 targeted PfSUB1, and this was confirmed by experimental evidence showing that PcFK1 inhibits PfSUB1 enzymatic activity. This outlines the usefulness of advanced bioinformatics tools to predict the function of a protein structure. The structural features of PcFK1 represent an interesting protein scaffold for future protein engineering.
authors.affiliation: Unité de Bioinformatique Structurale, Département de Biologie Structurale et Chimie, Paris, France.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Bastianelli
authors.forename: Anthony
authors.initials: A
authors.lastname: Bouillon
authors.forename: Christophe
authors.initials: C
authors.lastname: Nguyen
authors.forename: Elodie
authors.initials: E
authors.lastname: Crublet
authors.forename: Stéphane
authors.initials: S
authors.lastname: Pêtres
authors.forename: Olivier
authors.initials: O
authors.lastname: Gorgette
authors.forename: Dung
authors.initials: D
authors.lastname: Le-Nguyen
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Barale
authors.forename: Michael
authors.initials: M
authors.lastname: Nilges
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis / Q000187:drug effects; D052940:Merozoites / Q000166:cytology / Q000187:drug effects; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D010963:Plasmodium falciparum / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D015202:Protein Engineering / Q000379:methods*; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D059386:Reverse Genetics / Q000379:methods*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012997:Solvents; D013111:Spider Venoms / Q000737:chemistry / Q000494:pharmacology*; D020860:Subtilisin / Q000378:metabolism
chemical_list: D010455:Peptides; D015800:Protozoan Proteins; D012997:Solvents; D013111:Spider Venoms; D020860:Subtilisin