DSK2

DSK2 (PF3D7_1113400) is a ubiquitin-domain-containing shuttle protein of the Plasmodium falciparum ubiquitin-proteasome system that delivers ubiquitinated substrates to the proteasome (PMID:32057831). Its ubiquitin-like (UBL) domain adopts a distinct fold, resolved crystallographically at 1.30 Å, that carries an additional 3(10)-helix, an altered receptor-binding interface, and a reversed surface charge on its non-binding face relative to the human homolog, more closely resembling a HOIL-like E3 ligase UBL domain (PMID:32057831). The UBL domain binds the proteasomal receptors PfRpn10 and PfRpn13 with dissociation constants comparable to the human system, consistent with a conserved substrate-delivery role (PMID:32057831), and additionally engages the DEUBAD domain of PfRpn13, indicating an interaction landscape that may extend to cooperation with deubiquitinating enzymes during substrate proofreading (PMID:32057831). Beyond these structural and binding characterizations, the cellular and phenotypic roles of DSK2 have not been characterized in the available corpus.

1. 2020 High

   Whether the P. falciparum DSK2 UBL domain is structurally divergent from its human counterpart was unknown; an atomic-resolution structure established that the parasite domain has a unique architecture and surface chemistry that distinguishes it from HsDsk2.

   Evidence X-ray crystallography of the unbound PfDSK2 UBL domain at 1.30 Å

   PMID:32057831

   Open questions at the time

   • No structure of the full-length protein or of DSK2 in complex with its receptors
   • Functional consequence of the divergent surface charge and 3(10)-helix is not tested
   • The C-terminal UBA domain and substrate-binding end are not resolved
2. 2020 Medium

   It was unclear whether DSK2 functions as a proteasome shuttle in P. falciparum; quantitative binding to PfRpn10 and PfRpn13 with human-comparable affinities established DSK2 as a substrate shuttle protein.

   Evidence Biophysical dissociation-constant measurement of PfDSK2 UBL binding to PfRpn10 and PfRpn13

   PMID:32057831

   Open questions at the time

   • Binding shown for isolated UBL domain, not full-length protein
   • No demonstration of actual substrate delivery to the proteasome
   • Cellular requirement of these interactions untested
3. 2020 Medium

   Whether DSK2 could couple to deubiquitinating machinery was unknown; detection of a UBL–DEUBAD interaction with PfRpn13 hinted at a broader role in substrate proofreading.

   Evidence Biophysical interaction assay between PfRpn13 DEUBAD domain and PfDSK2 UBL domain

   PMID:32057831

   Open questions at the time

   • Single interaction assay, not independently replicated
   • Functional consequence for deubiquitination or proofreading is proposed but not tested
   • No evidence of a ternary DSK2–Rpn13–DUB assembly
4. 2023 Low

   Whether DSK2 is engaged in the cellular context by protease inhibitors was unexplored; thermal stabilization by E64d in intact infected erythrocytes indicated direct or indirect physical engagement of DSK2 in cells.

   Evidence Cellular thermal shift assay (CETSA/ITDR) with E64d in intact infected red blood cells; stabilization absent in lysate

   PMID:37232495

   Open questions at the time

   • Single chemo-proteomics experiment with an indirect thermal-stabilization readout and no mechanistic follow-up
   • Cannot distinguish direct binding from indirect engagement, especially given the lysate-negative result
   • No demonstration that E64d targets DSK2 function

• The cellular function, essentiality, substrate repertoire, and in vivo role of DSK2 in the P. falciparum proteasome pathway remain undefined.
• No genetic knockout or knockdown phenotype reported
• No ubiquitinated substrates identified
• No demonstration of proteasomal delivery in vivo