24pu | pdb_000024pu
The crystal structure of the chicken FANCM-MHF1-MHF2(Q74C) disulfide-crosslinked complex
Structural highlights
FunctionCENPS_CHICK DNA-binding component of the Fanconi anemia (FA) core complex. Required for the normal activation of the FA pathway, leading to monoubiquitination of the FANCI-FANCD2 complex in response to DNA damage, cellular resistance to DNA cross-linking drugs, and prevention of chromosomal breakage (PubMed:20347428). In complex with CENPX (MHF heterodimer), crucial cofactor for FANCM in both binding and ATP-dependent remodeling of DNA. Stabilizes FANCM. In complex with CENPX and FANCM (but not other FANC proteins), rapidly recruited to blocked forks and promotes gene conversion at blocked replication forks. In complex with CENPT, CENPW and CENPX (CENP-T-W-S-X heterotetramer), involved in the formation of a functional kinetochore outer plate, which is essential for kinetochore-microtubule attachment and faithful mitotic progression (PubMed:19620631). As a component of MHF and CENP-T-W-S-X complexes, binds DNA and bends it to form a nucleosome-like structure. DNA-binding function is fulfilled in the presence of CENPX, with the following preference for DNA substates: Holliday junction > double-stranded > splay arm > single-stranded. Does not bind DNA on its own (By similarity).[UniProtKB:Q8N2Z9][1] [2] Publication Abstract from PubMedThe Fanconi anemia complementation group M protein (FANCM)-MHF complex is required for branched DNA recognition in the Fanconi anemia pathway, but structural analysis of the intact complex has been hindered by dissociation of FANCM from the FANCM-associated histone fold (MHF) heterotetramer under crystallization conditions. Here, we used structure-guided disulfide engineering to stabilize the FANCM-MHF interface and test whether local geometry is sufficient to predict crosslinking specificity in a symmetric oligomeric assembly. Using endogenous FANCM Cys759 as an anchor, we designed two MHF2 variants, Q74C and L77C. Both supported oxidation-dependent crosslinking in the context of the FANCM-MHF complex, but with distinct outcomes. Q74C formed the intended FANCM-MHF2 disulfide, enabled crystallization of the intact heteropentamer, and preserved DNA-binding behavior under the tested conditions. In contrast, L77C favored a competing MHF2-MHF2 disulfide and yielded only the MHF heterotetramer after FANCM dissociation. Structural analysis further showed distinct crosslinking states for the two MHF tetramers in the asymmetric unit, consistent with local conformational heterogeneity at the MHF dimer-dimer interface. These results show that geometric plausibility alone does not predict crosslinking specificity in symmetric oligomers. Instead, symmetry-related competing pathways can redirect the reaction toward an alternative assembly state. This study provides a practical route to stabilizing FANCM-MHF and reveals a key design constraint for engineered disulfides in symmetric multimeric assemblies. Disulfide engineering of the FANCM-MHF complex reveals constraints on crosslink design in symmetric oligomers.,Ito S, Nishino T Protein Sci. 2026 Sep;35(9):e70761. doi: 10.1002/pro.70761. PMID:42606197[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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