title: Structure of a putative ClpS N-end rule adaptor protein from the malaria pathogen Plasmodium falciparum.
abstract: The N-end rule pathway uses an evolutionarily conserved mechanism in bacteria and eukaryotes that marks proteins for degradation by ATP-dependent chaperones and proteases such as the Clp chaperones and proteases. Specific N-terminal amino acids (N-degrons) are sufficient to target substrates for degradation. In bacteria, the ClpS adaptor binds and delivers N-end rule substrates for their degradation upon association with the ClpA/P chaperone/protease. Here, we report the first crystal structure, solved at 2.7 Å resolution, of a eukaryotic homolog of bacterial ClpS from the malaria apicomplexan parasite Plasmodium falciparum (Pfal). Despite limited sequence identity, Plasmodium ClpS is very similar to bacterial ClpS. Akin to its bacterial orthologs, plasmodial ClpS harbors a preformed hydrophobic pocket whose geometry and chemical properties are compatible with the binding of N-degrons. However, while the N-degron binding pocket in bacterial ClpS structures is open and accessible, the corresponding pocket in Plasmodium ClpS is occluded by a conserved surface loop that acts as a latch. Despite the closed conformation observed in the crystal, we show that, in solution, Pfal-ClpS binds and discriminates peptides mimicking bona fide N-end rule substrates. The presence of an apicoplast targeting peptide suggests that Pfal-ClpS localizes to this plastid-like organelle characteristic of all Apicomplexa and hosting most of its Clp machinery. By analogy with the related ClpS1 from plant chloroplasts and cyanobacteria, Plasmodium ClpS likely functions in association with ClpC in the apicoplast. Our findings open new venues for the design of novel anti-malarial drugs aimed at disrupting parasite-specific protein quality control pathways.
authors.affiliation: Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: AhYoung
authors.affiliation: Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California.
authors.forename: Antoine
authors.initials: A
authors.lastname: Koehl
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California.
authors.forename: Christina L
authors.initials: CL
authors.lastname: Vizcarra
authors.affiliation: Department of Energy Institute for Genomics and Proteomics, University of California at Los Angeles, Los Angeles, California.
authors.forename: Duilio
authors.initials: D
authors.lastname: Cascio
authors.affiliation: Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California.|Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California.
authors.forename: Pascal F
authors.initials: PF
authors.lastname: Egea
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D049071:Endopeptidase Clp / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D016778:Malaria, Falciparum / Q000469:parasitology; D008958:Models, Molecular; D010963:Plasmodium falciparum / Q000737:chemistry* / Q000201:enzymology* / Q000378:metabolism; D011487:Protein Conformation; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D049071:Endopeptidase Clp
keywords: Clp chaperone; Clp protease; ClpS; N-degron; N-end rule; apicoplast; carrier-assisted crystallization; crystal structure; drug target; malaria; organelle; phylogeny; plasmodium; plastid