A flexible loop in the Smc3 head domain is required for stability and cohesin complex integrity

Q: What is the clinical evidence from this study?

Population: Cornelia de Lange syndrome (CdLS). Intervention: Smc3 head domain loop deletion (smc3ΔL1) vs. Wild-type SMC3. Primary outcome: Premature sister chromatid cohesion loss (presence of two GFP dots).

Q: What does this research mean for the field?

A flexible loop within the Smc3 head domain is required for protein stability, interaction with the kleisin subunit Scc1, and maintaining sister chromatid cohesion. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

Wisal Asaad; Avi Matityahu; Itay Onn

doi:10.1038/s41598-026-57337-0

June 25, 2026Scientific ReportsOpen Access

A flexible loop in the Smc3 head domain is required for stability and cohesin complex integrity

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Key result

Smc3 loop deletion destabilizes cohesin, triggering premature chromatid cohesion loss in ~90% of cells.

Why the study?

Smc3 is essential for cohesin complex function and linked to Cornelia de Lange syndrome, but the role of a flexible loop within its head domain was uncharacterized.

Key Points

To identify and characterize the functional role of a flexible loop within the Smc3 head domain in cohesin complex integrity and sister chromatid cohesion.
Generated Saccharomyces cerevisiae strains bearing an auxin-inducible degron (SMC3-AID) along with wild-type or mutant SMC3 alleles (loop deletion smc3ΔL1, three-residue deletion smc3ΔL1-1, P92A, and S93D).
Evaluated sister chromatid cohesion using a LacO/LacI-GFP dot assay, cohesin chromatin binding using ChIP-qPCR at centromeres and chromosome arm loci, and subunit interactions by co-immunoprecipitation.
In the absence of functional Smc3 or in cells carrying smc3ΔL1, approximately 90% of cells exhibited two GFP dots indicating premature cohesion loss, compared with about 5% of wild-type SMC3 cells.
Deletion of the loop (smc3ΔL1) significantly reduced cohesin binding across all tested chromatin regions and impaired co-precipitation with the kleisin subunit Scc1, without altering Smc1-Smc3 hinge dimerization.
The smc3ΔL1 allele, the smc3ΔL1-1 mini-deletion, and single point mutations (P92A and S93D) compromised protein stability and failed to support cell viability upon auxin-mediated degradation of wild-type Smc3.

Structured PICO

P

Population

Smc3 subunit of the cohesin complex

I

Intervention

Deletion or mutation of a flexible loop within the head domain of Smc3

O

Outcome

Protein stability, cohesin activity, and interaction with the kleisin subunit Scc1

Main Result

Absolute Event Rate: 90% vs 5%

Limitations

Incomplete structural data of Smc3 in complex with Scc1 from humans and yeast

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Implication

Identifies a critical flexible loop in the Smc3 head domain essential for cohesin complex integrity, providing a basis for reclassifying variants of unknown significance in Cornelia de Lange syndrome as pathogenic.

Abstract

Smc3 is a core subunit of the cohesin complex and is essential for its biological function. Cohesin, an evolutionarily conserved complex of the Structural Maintenance of Chromosomes (SMC) family, mediates the higher-order organization of chromatin and plays a crucial role in maintaining genome stability and dynamics. Mutations in human SMC3 are associated with Cornelia de Lange syndrome (CdLS), a rare genetic disorder characterized by cognitive and physical developmental delays. This study identified a flexible loop within the head domain of Smc3 and investigated its function. This loop was demonstrated to have an essential role in cohesin activity, specifically by mediating the interaction with the kleisin subunit Scc1. Deletion of this loop or mutation of residues within it destabilizes the protein, affecting cohesion and its enrichment on chromatin in cells. By assigning a functional role to this loop region, single-nucleotide variants of unknown clinical significance (VUS), previously identified in Cornelia de Lange syndrome patients, can be re-examined and suggested for classification as pathogenic. This work enhances the understanding of the structure–function relationship of Smc3 and its impact on human health.

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Cite This Study

Asaad et al. (2026) studied Cornelia de Lange syndrome (CdLS). Smc3 head domain loop deletion (smc3ΔL1) vs. Wild-type SMC3 was evaluated on Premature sister chromatid cohesion loss (presence of two GFP dots). Deletion of a flexible loop in the Smc3 head domain caused premature sister chromatid cohesion loss in approximately 90% of cells compared to 5% in wild-type cells, destabilizing the cohesin complex.

synapsesocial.com/papers/6a3f6b65aea7db3c19540a81 https://doi.org/10.1038/s41598-026-57337-0

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A flexible loop in the Smc3 head domain is required for stability and cohesin complex integrity

Key Points

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

A flexible loop in the Smc3 head domain is required for stability and cohesin complex integrity

Key Points

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

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