{"id":"ab04b039-4588-4b7b-8aa5-ee682adb200c","arxiv_id":"2606.04766","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":5.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":1,"one_line_summary":"Protein architecture and rotational flexibility between structured and unstructured regions tune supramolecular filament lengths by shifting distributions toward shorter polymers compared to isolated driving domains.","lead":"The paper shows that the yeast protein Bem1 forms long filaments via its PB1 domain but much shorter assemblies when the full architecture including unstructured regions is present. A smart generalist might read it to see how protein shape and charge act as control knobs for building tunable molecular structures in cells.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Minimal 5/6-bead CG models may omit interactions or states that change length distributions, undermining attribution of deviation to rotational flexibility.","rationale":"The reader's weakest_assumption directly identifies the same load-bearing point. Because the review was abstract-only, the full text may contain supporting checks, but the concern remains the most direct threat to the quantitative claims about Flory agreement and the origin of the 6-bead deviation. No other internal inconsistency is evident from the given material.","tokens_in":1823,"tokens_out":328,"duration_ms":31650,"concrete_test":"Re-run the 6-bead simulations after increasing the number of beads representing the unstructured region or adding explicit side-chain charges; if the shift toward shorter polymers disappears or the exponent deviates from the reported value, the minimal model does not isolate the claimed mechanism.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that the 5-bead model quantitatively reproduces reversible Flory polymerization (tunable by charge polarity) while the 6-bead model deviates solely because of steric/geometric effects from the extra bead and its rotational flexibility. This holds only if the coarse-grained representations contain no missing specific interactions, charge placements, or conformational ensembles that would alter the observed weight distributions in the real Bem1 system. The abstract states these are 'minimal' approximations; if the full text does not demonstrate robustness (e.g., via parameter sweeps or comparison to atomistic data), the quantitative match and the identification of rotational flexibility as the key parameter rest on an untested assumption about model sufficiency.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript claims that charge heterogeneity and protein architecture tune supramolecular polymerization in the multidomain protein Bem1. Experiments show the isolated PB1 domain forms extended filaments while full-length Bem1 forms shorter assemblies. Minimal 5-bead and 6-bead coarse-grained models are introduced, with the 5-bead model reported to quantitatively match reversible Flory-like polymerization (tunable in a narrow charge-polarity regime) and the 6-bead model producing shorter polymers due to steric/geometric constraints and rotational flexibility between the structured domain and appended unstructured region.","tokens_in":2018,"tokens_out":425,"duration_ms":22900,"significance":"If the central claims hold after addressing model validation, the work would establish charge polarity, architecture, and conformational flexibility as programmable knobs for controlling assembly size in multidomain proteins, offering a general framework linking experiment, minimal CG models, and Flory theory for biomolecular self-assembly.","major_comments":[{"comment":"Abstract: the claim of quantitative agreement between the 5-bead model weight distributions and reversible Flory-like polymerization theory provides no error bars, fit statistics, or details on how the narrow charge polarity regime was identified or tested for robustness.","section":"Abstract"},{"comment":"Abstract: the 6-bead model is constructed to reproduce the experimental observation of shorter assemblies; this creates circularity when the same model is then used to identify rotational flexibility as the governing parameter for the deviation from Flory behavior.","section":"Abstract"},{"comment":"Abstract: the central attribution of the length-distribution shift to rotational flexibility and steric constraints rests on the untested assumption that the minimal 5-bead/6-bead representations contain no missing specific interactions, charge placements, or conformational states that would alter the observed distributions in real Bem1; no parameter sweeps, atomistic comparisons, or experimental filament-length validation are described.","section":"Abstract"}],"minor_comments":[],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the constructive comments on our manuscript. We address each major point below and have revised the manuscript where appropriate to strengthen the presentation of the modeling results and their limitations.","responses":[{"response":"We agree that the abstract and main text should provide more quantitative detail on the agreement. In the revised manuscript we add error bars to the weight distributions in Figure 3, report chi-squared and R-squared statistics for the Flory fits, and include a new supplementary section that describes the systematic scan over charge polarity values used to identify the narrow regime together with robustness checks against small perturbations in bead charges and interaction cutoffs.","revision_made":"yes","referee_comment":"[Abstract] Abstract: the claim of quantitative agreement between the 5-bead model weight distributions and reversible Flory-like polymerization theory provides no error bars, fit statistics, or details on how the narrow charge polarity regime was identified or tested for robustness."},{"response":"We disagree that the construction introduces circularity. The 6-bead representation was built directly from the known domain architecture of Bem1 by appending a single bead for the remainder of the protein to the validated 5-bead PB1 model; no length-distribution target was imposed during parameterization. The emergence of shorter polymers is an outcome of the added steric volume and rotational freedom, which we then analyze by comparing orientational correlation functions and effective persistence lengths between the two models. We have clarified this workflow in the revised methods and results sections.","revision_made":"no","referee_comment":"[Abstract] Abstract: the 6-bead model is constructed to reproduce the experimental observation of shorter assemblies; this creates circularity when the same model is then used to identify rotational flexibility as the governing parameter for the deviation from Flory behavior."},{"response":"We acknowledge that minimal models necessarily omit atomistic detail. In revision we add extensive parameter sweeps over interaction strengths, bead diameters, and linker flexibility (new Supplementary Figures S5–S7) that confirm the shift toward shorter polymers remains robust. Atomistic comparisons lie outside the scope of the present minimal-model study; we have added an explicit limitations paragraph discussing this assumption. Experimental filament-length distributions are already reported for both isolated PB1 and full-length Bem1 (Figure 2), and the models are calibrated only to the observed qualitative trend rather than to absolute lengths.","revision_made":"partial","referee_comment":"[Abstract] Abstract: the central attribution of the length-distribution shift to rotational flexibility and steric constraints rests on the untested assumption that the minimal 5-bead/6-bead representations contain no missing specific interactions, charge placements, or conformational states that would alter the observed distributions in real Bem1; no parameter sweeps, atomistic comparisons, or experimental filament-length validation are described."}],"tokens_in":1458,"tokens_out":606,"duration_ms":28292,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The paper reports that isolated PB1 domains form long filaments while full-length Bem1 produces shorter ones, and their coarse-grained models link the difference to rotational flexibility between the structured domain and the added unstructured bead.\n\nThe experimental comparison is the clearest part. It establishes that the PB1 domain drives assembly while the rest of the protein limits length, which is a direct observation worth noting for multidomain signaling proteins.\n\nThe modeling applies standard reversible Flory polymerization to the 5-bead case and shows a shift in the 6-bead case. That extension to protein architecture is incremental but fits the subfield.\n\nThe soft spots sit in the models. The 6-bead representation is constructed to reproduce the shorter experimental lengths, so identifying rotational flexibility as the controlling parameter comes from the same setup that was adjusted to fit the data. The abstract gives no error bars on the weight distributions, no justification for the specific charge polarity choices, and no checks that the minimal beads reproduce actual filament lengths or miss key interactions. If those assumptions do not hold, the claim that flexibility governs self-limited assembly rests on untested model sufficiency.\n\nThis is for groups working on biomolecular self-assembly and synthetic design. The experimental result could be useful to them, but the modeling conclusions need more validation to stand.\n\nSend it for peer review. The experimental finding is concrete enough to merit referee time, though the model claims will likely draw questions on robustness.","headline":"Experiments show full-length Bem1 makes shorter assemblies than PB1 alone, but the 6-bead model attributes the shift to rotational flexibility after being built to match that outcome.","tokens_in":2508,"tokens_out":374,"would_cite":false,"duration_ms":31015,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"Protein architecture and rotational flexibility between domains tune the length of supramolecular filaments assembled by multidomain proteins.","keywords":["supramolecular polymerization","protein architecture","charge heterogeneity","coarse-grained models","filament length distribution","rotational flexibility","self-limited assembly"],"falsifier":"Direct measurement of filament length distributions for Bem1 constructs whose linker regions have been mutated to change rotational flexibility or charge polarity, compared against the model's quantitative predictions.","tokens_in":2738,"feed_emoji":"🧬","tokens_out":671,"duration_ms":28814,"temperature":0.7,"pith_summary":"The paper establishes that the isolated PB1 domain of Bem1 assembles into extended filaments whose length distributions follow reversible Flory-like polymerization and can be tuned by charge polarity. Full-length Bem1 forms shorter assemblies because the additional unstructured regions impose steric and geometric constraints. The key physical parameter is the rotational flexibility between the structured polar domain and the appended region. A sympathetic reader would care because this mechanism shows how cells can program the size of self-assembled structures using only protein architecture and charge without needing extra binding partners.","feed_headline":"Unstructured regions limit protein filament length via flexibility","feed_subtitle":"5-bead and 6-bead models show charge polarity tunes assembly while appended domains shorten polymers through rotational constraints.","key_machinery":"Rotational flexibility between the charge-polar structured domain and the unstructured region, which generates steric constraints that shift the 6-bead model toward shorter polymers relative to the 5-bead model.","core_discovery":"The weight distribution of supramolecular filaments assembled by the 5-bead model quantitatively follows reversible Flory-like polymerization theory, which is tunable within a narrow charge polarity regime. In contrast, the 6-bead model shifts chain-length distributions towards shorter polymers despite retaining the same driving domain. This deviation arises from steric and geometric constraints imposed by the appended unstructured regions, where rotational flexibility between the charge-polar structured domain and the unstructured region emerges as the key physical parameter governing self-limited self-assembly.","pith_inferences":["Cells could exploit this architecture-based control to adjust signaling complex sizes through mutations or modifications that alter linker flexibility.","The same principle may operate in other multidomain proteins where one domain drives polymerization and others limit extent.","Varying the length or stiffness of the unstructured segment in the model would produce a continuous family of length distributions for experimental test.","This offers a route to design synthetic multidomain proteins with programmable assembly sizes using only charge and flexibility parameters."],"forward_implications":["Charge polarity within a narrow regime controls filament length distributions in the driving domain.","Appending unstructured regions to a polar assembly domain produces self-limited shorter polymers.","Rotational flexibility acts as the physical parameter that enforces the shift to shorter chain lengths.","The PB1 domain alone drives extended assembly while the full protein architecture tunes the outcome."],"fun_headline_variants":["Flexibility from unstructured regions shortens protein filaments","Charge polarity tunes reversible polymerization in bead models","Appended domains limit assembly length via rotational flexibility","6-bead model shows architecture curbs filament growth"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The minimal 5-bead and 6-bead coarse-grained models capture the essential physics of Bem1 assembly without missing specific interactions or conformational states that would alter the observed length distributions.","fun_headline_variants_meta":{"raw":{"variants":["Flexibility from unstructured regions shortens protein filaments","Charge polarity tunes reversible polymerization in bead models","Appended domains limit assembly length via rotational flexibility","6-bead model shows architecture curbs filament growth"]},"model":"grok-4.3","cost_usd":0.005622,"raw_usage":{"total_tokens":2731,"prompt_tokens":749,"num_sources_used":0,"completion_tokens":56,"cost_in_usd_ticks":56224500,"prompt_tokens_details":{"text_tokens":749,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1926,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":749,"tokens_out":56,"duration_ms":22122,"temperature":1.0,"reasoning_tokens":1926,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-06-28T03:48:25.275772+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"Direct measurement of filament length distributions for Bem1 constructs whose linker regions have been mutated to change rotational flexibility or charge polarity, compared against the model's quantitative predictions.","supporting_citations":[],"review_version":1}