NEDD8

PF3D7_1313000 (PfNEDD8) is a 76-amino-acid ubiquitin-like modifier that functions in a protein neddylation pathway, becoming covalently conjugated to target proteins to regulate their activity (PMID:33214620). It lacks a C-terminal tail and is conjugated directly through Gly76, since a Gly75Ala/Gly76Ala double mutant abolishes formation of high-molecular-weight conjugates; immunoprecipitation-mass spectrometry and cross-species complementation in yeast identify parasite cullins as its physiological substrates (PMID:33214620). Deconjugation of PfNEDD8 is carried out by parasite UCH-family hydrolases with dual ubiquitin/NEDD8 specificity, including PfUCHL3, PfUCHL54, and PfUCH37, and this deNeddylation machinery is configured differently from the human host (PMID:20042598, PMID:16925553, PMID:31658303). Genetically, the pathway is dispensable for blood-stage growth in P. berghei but is essential for the zygote-to-ookinete transition and mosquito transmission (PMID:38411954).

1. 2006 Medium

   The first question was whether P. falciparum encodes enzymes capable of removing PfNEDD8 from targets, which was answered by identifying a parasite deNeddylase.

   Evidence Nedd8-based activity-based chemical probe labelling and functional proteomic identification of PfUCHL54 in P. falciparum

   PMID:16925553

   Open questions at the time

   • Does not identify neddylated substrates of PfNEDD8
   • Single method/single lab without genetic validation of essentiality
2. 2007 Medium

   To understand the origin of dual specificity, the deNeddylating activity of UCHL3 orthologs was tested, establishing that PfNEDD8 can be processed by an enzyme also active on ubiquitin.

   Evidence Activity-based chemical probes and phylogenetic analysis of P. falciparum and T. gondii UCHL3, with T. gondii UCHL3 crystal structure

   PMID:17371404

   Open questions at the time

   • Plasmodium-specific structural detail less resolved than T. gondii
   • Does not address conjugation machinery or in-parasite substrates
3. 2009 High

   The structural basis for how a single parasite hydrolase recognizes PfNEDD8 was resolved, explaining dual ubiquitin/NEDD8 specificity at the atomic level.

   Evidence Crystal structures of PfUCHL3 and a PfUCHL3–UbVME suicide-substrate complex plus molecular dynamics simulation of a PfUCHL3–PfNEDD8 model

   PMID:20042598

   Open questions at the time

   • PfNEDD8 binding modeled rather than crystallized directly
   • Biological importance of deNeddylation not yet tested genetically
4. 2019 Medium

   Whether PfNEDD8 deconjugation activity of a dual-specificity hydrolase is essential was tested, showing that deNeddylation and deubiquitination roles can be functionally separated in the parasite.

   Evidence Activity-based probes, parasite transgenics, and drug assays characterizing PfUCH37 active-site determinants in P. falciparum

   PMID:31658303

   Open questions at the time

   • Essentiality attributed to ubiquitin, not NEDD8, activity
   • Direct substrates deconjugated in vivo not enumerated
5. 2020 High

   The core conjugation chemistry and physiological substrates of PfNEDD8 were defined, establishing it as a bona fide cullin-modifying neddylation system.

   Evidence Gly75Ala/Gly76Ala mutagenesis in P. falciparum, IP-mass spectrometry, and complementation in S. cerevisiae rub1Δ and ubc12Δ strains retrieving cullins

   PMID:33214620

   Open questions at the time

   • E1/E2 activating and conjugating enzymes for PfNEDD8 not characterized
   • Functional consequence of cullin neddylation on CRL activity not measured
6. 2024 High

   The in vivo requirement for the pathway across the life cycle was defined, revealing a stage-specific essential role rather than a general growth requirement.

   Evidence Genetic knockout, life-cycle phenotyping, and genetic complementation of Nedd8 in P. berghei

   PMID:38411954

   Open questions at the time

   • Molecular targets driving the ookinete transition defect unidentified
   • Shown in P. berghei; falciparum transmission requirement not directly tested

• The identity of the PfNEDD8 activating/conjugating enzymes and the specific cullin-RING ligase substrates whose regulation underlies the essential zygote-to-ookinete transition remain unknown.
• No E1/E2 conjugation machinery characterized for PfNEDD8
• Link between cullin neddylation and the mosquito-stage phenotype unresolved