MCMBP

In Plasmodium falciparum, MCMBP (PF3D7_1412100) is a stable accessory subunit of the MCM replicative helicase complex, physically associating with the MCM2–7 subunits by co-purification and confirmed by reciprocal immunoprecipitation of PfMCM4-FLAG, which enriches MCMBP together with MCM2/3/5/6/7 (PMID:33124706, PMID:40592953). Despite this association with the DNA replication machinery, MCMBP's essential role during schizogony is in nuclear division rather than DNA synthesis: conditional depletion disrupts nuclear morphology and parasite proliferation without blocking DNA replication (PMID:33124706, PMID:34835432). Loss of MCMBP produces aberrant hemispindles and mitotic spindles (~30% longer with additional branches), anaphase chromatin bridges, individual nuclei bearing multiple microtubule structures, and abnormal centrin distribution, establishing a requirement for MCMBP in mitotic spindle integrity, centrosome function, and chromosome segregation (PMID:33124706, PMID:34835432). Because MCMBP-deficient parasites nonetheless complete cytokinesis and form aneuploid merozoites of variable size, karyokinesis and cytokinesis are not coupled by a robust checkpoint in this organism (PMID:33124706). The abundance of MCMBP and the MCM subunits is negatively regulated by CRL ubiquitin ligase activity, as knockdown of the CRL component PfRBX1 raises their protein levels (PMID:40592953).

1. 2020 Medium

   Whether PF3D7_1412100 associates with the replication machinery was unknown; co-purification placed it physically within the MCM replicative helicase complex, defining it as an MCM-associated protein in blood-stage parasites.

   Evidence Co-purification with mass spectrometry in P. falciparum blood stages

   PMID:33124706 PMID:40592953

   Open questions at the time

   • Does not resolve whether the association is direct or which MCM subunit MCMBP contacts
   • Stoichiometry and structural arrangement within the complex not defined
2. 2020 High

   It was unclear whether MCMBP acts in DNA replication like the core helicase or in a distinct process; conditional depletion showed it is required for normal karyokinesis but dispensable for DNA replication, uncoupling its function from bulk genome synthesis.

   Evidence Inducible conditional knockdown with proliferation assay, IFA for nuclear morphology, and DNA replication readout in P. falciparum

   PMID:33124706 PMID:34835432

   Open questions at the time

   • Molecular mechanism linking an MCM-associated protein to karyokinesis not defined
   • Whether the karyokinesis defect is a direct MCMBP function or a downstream consequence unresolved
3. 2020 Medium

   The nature of the nuclear defect was undefined; depletion was shown to disrupt mitotic spindle organization and centrin distribution, and to permit cytokinesis despite aberrant karyokinesis, revealing the absence of a karyokinesis-to-cytokinesis checkpoint and production of aneuploid merozoites.

   Evidence Conditional knockdown with anti-tubulin/anti-centrin IFA, flow cytometry, and microscopy of merozoite nuclear content in P. falciparum

   PMID:33124706

   Open questions at the time

   • How MCMBP influences spindle and centrin behavior mechanistically not established
   • Single-lab observation for the checkpoint-absence and aneuploidy phenotype
4. 2021 Medium

   The spindle phenotype was described only at conventional resolution; ultrastructure expansion microscopy refined it, revealing aberrant hemispindles, elongated over-branched spindles, anaphase chromatin bridges, and nuclei with multiple microtubule structures, sharpening the segregation-defect picture.

   Evidence U-ExM with a novel nuclear envelope stain and anti-tubulin labeling following conditional knockdown in P. falciparum

   PMID:34835432

   Open questions at the time

   • Does not establish whether the spindle defects originate from MCMBP's role at centrosomes, chromatin, or spindle microtubules directly
   • Single-lab imaging study
5. 2025 Low

   Whether MCMBP resides only within the MCM complex or has a broader spatial neighborhood was untested; proximity labeling placed it near an uncharacterized protein PfAnchor and apicoplast-associated proteins, hinting at a wider spatial network.

   Evidence BirA-based proximity labeling with mass spectrometry using MCMBP-BirA-HA as bait in P. falciparum 3D7

   PMID:41309594

   Open questions at the time

   • Proximity labeling does not establish direct physical interaction
   • No reciprocal validation for MCMBP; functional significance of PfAnchor proximity unknown
6. 2025 Medium

   The MCM-complex membership of MCMBP rested on one co-purification; reciprocal IP of PfMCM4-FLAG confirmed MCMBP as a stable co-purifying subunit alongside MCM2/3/5/6/7, while showing MCM8/MCM9 are not part of this complex.

   Evidence Immunoprecipitation of FLAG-tagged PfMCM4 followed by LC-MS/MS in P. falciparum asexual blood stages

   PMID:40592953

   Open questions at the time

   • Does not map direct contacts or the position of MCMBP within the complex
   • Complex composition determined in asexual stages only
7. 2025 Low

   How MCMBP/MCM abundance is controlled was unknown; knockdown of the CRL E3 component PfRBX1 raised levels of MCMBP and all six MCM subunits, implicating CRL ubiquitin ligase activity in negatively regulating their stability.

   Evidence Conditional knockdown of PfRBX1 with western blot quantification of MCMBP and MCM subunit levels in P. falciparum

   PMID:40592953

   Open questions at the time

   • Indirect evidence via an upstream regulator; direct ubiquitination of MCMBP not demonstrated
   • Single lab, single method (western blot after knockdown)

• The direct molecular mechanism by which an MCM-complex-associated protein controls mitotic spindle organization, centrosome/centrin behavior, and chromosome segregation during schizogony remains unresolved.
• No structural model of MCMBP within the MCM complex
• No defined biochemical activity of MCMBP toward spindle or centrosome components
• Whether the CRL-mediated regulation is functionally coupled to the karyokinesis role unknown