X-ray Crystal Structure and Specificity of the Plasmodium falciparum Malaria Aminopeptidase PfM18AAP

• Published in: Journal of molecular biology 2012-09, Vol.422 (4), p.495-507
• Main Authors: Sivaraman, Komagal Kannan, Oellig, Christine A., Huynh, Kitmun, Atkinson, Sarah C., Poreba, Marcin, Perugini, Matthew A., Trenholme, Katharine R., Gardiner, Donald L., Salvesen, Guy, Drag, Marcin, Dalton, John P., Whisstock, James C., McGowan, Sheena
• Format: Article
• Language: English
• Subjects: active sites; amino acids; Amino Acids - chemistry; Amino Acids - metabolism; aminopeptidase; aminopeptidases; Aminopeptidases - chemistry; Aminopeptidases - metabolism; Animals; antisense RNA; Catalytic Domain; Crystallography, X-Ray - methods; drug design; drugs; Erythrocytes - metabolism; hemoglobin; Humans; malaria; Malaria, Falciparum - enzymology; Malaria, Falciparum - parasitology; parasites; peptides; Peptides - chemistry; Peptides - metabolism; Plasmodium falciparum; Plasmodium falciparum - enzymology; protease; Proteolysis; Protozoan Proteins - chemistry; Protozoan Proteins - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; structural biology; Substrate Specificity; X-ray diffraction
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2012.06.006

The malarial aminopeptidases have emerged as promising new drug targets for the development of novel antimalarial drugs. The M18AAP of Plasmodium falciparum malaria is a metallo-aminopeptidase that we show demonstrates a highly restricted specificity for peptides with an N-terminal Glu or Asp residue. Thus, the enzyme may function alongside other aminopeptidases in effecting the complete degradation or turnover of proteins, such as host hemoglobin, which provides a free amino acid pool for the growing parasite. Inhibition of PfM18AAP's function using antisense RNA is detrimental to the intra-erythrocytic malaria parasite and, hence, it has been proposed as a potential novel drug target. We report the X-ray crystal structure of the PfM18AAP aminopeptidase and reveal its complex dodecameric assembly arranged via dimer and trimer units that interact to form a large tetrahedron shape that completely encloses the 12 active sites within a central cavity. The four entry points to the catalytic lumen are each guarded by 12 large flexible loops that could control substrate entry into the catalytic sites. PfM18AAP thus resembles a proteasomal-like machine with multiple active sites able to degrade peptide substrates that enter the central lumen. The Plasmodium enzyme shows significant structural differences around the active site when compared to recently determined structures of its mammalian and human homologs, which provides a platform from which a rational approach to inhibitor design of new malaria-specific drugs can begin. [Display omitted] ► The PfM18AAP aminopeptidase is a potential antimalarial drug target. ► The enzyme shows highly restricted specificity. ► Resolution of the X-ray crystal structure reveals a complex dodecameric assembly. ► PfM18AAP shows structural differences in comparison to mammalian and human homologs. ► These data provide a platform from which a rational approach to inhibitor design can begin.