Recombinant expression and enzymatic subsite characterization of plasmepsin 4 from the four Plasmodium species infecting man.
Plasmepsin 4 from Plasmodium falciparum and orthologs from Plasmodium malariae, Plasmodium ovale and Plasmodium vivax have been expressed in recombinant form, and properties of the active site of each enzyme characterized by kinetic analysis. A panel of chromogenic peptide substrates systematically substituted at the P3, P2, P2' and P3' positions was used to estimate enzyme/ligand interactions in the corresponding enzyme subsites based upon kinetic data. The kinetic parameters kcat, Km and kcat/Km were measured to identify optimal substrates for each enzyme and also sequences that were readily cleaved by the plasmepsins but poorly by host aspartic peptidases. Computer generated models were utilized to compare enzyme structures and interpret kinetic results. The orthologous plasmepsins share highly similar subsite specificities. In the S3 and S2 subsites, the plasmepsin 4 orthologs all preferred hydrophobic amino acid residues, Phe or Ile, but rejected charged residues such as Lys or Asp. In S2' and S3' subsites, these plasmepsins tolerated both hydrophobic and hydrophilic residues. Subsite specificities of the plasmepsin 4 family of orthologs are similar to those of human cathepsins D and E, except in S3' where the plasmepsins accept substrates containing Ser significantly better than either of these human aspartic proteases. Peptidomimetic methyleneamino reduced-peptide inhibitors, which have inhibition constants in the picomolar range, were prepared for each plasmepsin 4 ortholog based upon substrate preferences. A peptidomimetic inhibitor designed for plasmepsin 4 from P. falciparum having Ser in P3' had the lowest Ki of the series of inhibitors prepared, but did not significantly improve the selectivity of the inhibitor for plasmepsin 4 versus human cathepsin D.
Li
Tang
T
Department of Pathobiology, University of Florida, P.O. Box 110880, Gainesville, FL 32611-0880, USA.
Yowell
Charles A
CA
Beyer
Bret B
BB
Hung
Su-Hwi
SH
Westling
Jennifer
J
Lam
Minh T
MT
Dunn
Ben M
BM
Dame
John B
JB
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D002402:Cathepsin D / Q000378:metabolism; D020059:Cathepsin E / Q000378:metabolism; D002863:Chromogenic Compounds / Q000378:metabolism; D003198:Computer Simulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D010963:Plasmodium falciparum / Q000235:genetics / Q000378:metabolism*; D010965:Plasmodium malariae / Q000235:genetics / Q000378:metabolism*; D041122:Plasmodium ovale / Q000235:genetics / Q000378:metabolism*; D010966:Plasmodium vivax / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D002863:Chromogenic Compounds; D004791:Enzyme Inhibitors; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D016282:Aspartic Acid Endopeptidases; D020059:Cathepsin E; C089643:plasmepsin; D002402:Cathepsin D