AIGR TreeGrafter Function-Inference Stress Test Falcon Edison Scientific Literature 23 citations 3 artifacts 2026-06-24T04:28:45.197620 citations file

AIGR TreeGrafter Function-Inference Stress Test

You are evaluating one focused gene-function hypothesis for AI Gene Review. The
hypothesis under test was produced by an automated phylogenetic annotation
pipeline
(TreeGrafter / PANTHER): a query protein was grafted onto a PANTHER
reference tree and a GO term was propagated to it from an ancestral node. Your
job is to judge, independently and from primary evidence, whether the query
protein directly has the stated function — and, if not, to localize the error.

This is not a general gene overview. Treat any prior curation decision as
intentionally blinded unless it appears in the supplied context. Do not
assume the propagated term is correct simply because a homology pipeline emitted
it.

Target Gene

Focus

Seed Hypothesis (propagated by TreeGrafter/PANTHER)

OCTS1 has glutathione transferase activity (GO:0004364).

Term and Decision Context

Reference Context

Source Context YAML

term:
  id: GO:0004364
  label: glutathione transferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000118

Research Objective

Decide whether OCTS1 directly has the stated function. Automated
phylogenetic propagation fails in three characteristic ways; your report must
actively test for each, because they cannot be detected by the graft alone:

  1. Granularity / family-vs-subfamily. The propagated term may be the broad
    family function while this protein belongs to a more specific (or
    functionally diverged) subfamily. Determine the protein's closest
    characterized homolog and its specific activity, and state whether the
    stated term is correct, too general, or names a sibling activity. (Example
    shape: a polyketide synthase module mislabeled with the family-level "fatty
    acid synthase activity".)
  2. Pseudo-enzyme / loss of activity. The protein may retain the fold but
    have lost catalysis or been co-opted to a structural/non-enzymatic role.
    Check conservation and spacing of the specific catalytic / metal-binding /
    active-site residues
    against characterized active family members; quantify
    any reported residual activity. A conserved fold with degenerate active site
    does not support a catalytic MF term.
  3. Within-superfamily mis-placement. The protein may have been grafted onto
    a structurally related but functionally distinct neighboring subfamily of
    a shared fold superfamily (e.g. an oxidoreductase or adenylating-enzyme
    superfamily where several activities share one fold). Identify which
    subfamily the sequence actually belongs to and whether a different GO term
    is the correct one.

Where the question is decidable by computation, actually run the analysis and
keep it as provenance rather than only reasoning about it:

Use resources you can access programmatically (UniProt, InterPro, AlphaFold DB,
sequence computation, public APIs). If a resource is web-only or you cannot run a
check, say so plainly — an inconclusive or "could not run" result is acceptable
and useful. Never fabricate a result. Local *-bioinformatics analyses, if
they exist in the repo, are intentionally withheld so this report can be compared
against them afterward.

Required Output

Executive Judgment

Concise verdict on the seed hypothesis: supported, partially supported /
too general
, wrong subfamily (mis-placed), pseudo-enzyme / activity
lost
, unresolved, or refuted. Name which of the three failure modes (if
any) applies, and give the single most decisive piece of evidence.

Independent Family/Function Assignment

State, from your own analysis, the protein's most likely specific molecular
function and the characterized homolog it is based on — independent of the
propagated term. Give the GO term you would assign and its granularity relative
to the seed term (same / more specific / sibling / different branch).

Evidence Matrix

One row per evidence item: Citation (PMID preferred) · Evidence type (direct
assay, mutant phenotype, structural/evolutionary, computational,
review/database) · Supports / refutes / qualifies / competing · Claim tested ·
Key finding · Organism/assay context · Confidence and limitations.

Active-Site / Placement Analysis

Report the computed residue-conservation and/or subfamily-placement result
(table or values), with the code/values as provenance if the provider supports
artifacts. State explicitly whether catalytic residues are intact.

GO Curation Implications

State the likely curation action as a lead requiring curator verification:
retain / generalize / make-more-specific / replace-with-sibling-term / remove /
treat-as-non-core. Avoid "protein binding" as a final recommendation.

Conflicts, Knowledge Gaps, Discriminating Tests

Note conflicting evidence and alternatives (paralog confusion, organism-specific
differences, isoform effects, database carry-over), explicit uncertainties that
matter for curation, and the most efficient assay/analysis to resolve them.

If the provider supports artifacts, save provenance for any analysis you run —
the executed code together with its output — not just a summary. Do not
synthesize a figure implying an analysis you did not run.

AIGR TreeGrafter Function-Inference Stress Test Report: OCTS1 (P27013) — GO:0004364 Glutathione Transferase Activity

Executive Judgment

Verdict: Pseudo-enzyme / activity lost. The seed hypothesis that OCTS1 has glutathione transferase activity (GO:0004364) is not supported as a primary molecular function annotation. This represents failure mode #2 (pseudo-enzyme / loss of activity).

OCTS1 (UniProt P27013) is S-crystallin 1 from Octopus vulgaris, a sigma-class GST-derived protein that has been evolutionarily co-opted as a structural lens crystallin. While it retains the canonical GST fold and strong glutathione (GSH) binding, its catalytic efficiency toward electrophilic substrates is reduced approximately 700-fold in kcat and ~6,000-fold in catalytic efficiency (kcat/Km,CDNB) relative to the authentic octopus GST-σ enzyme (tan2016structureofa pages 2-4, tan2016structureofa pages 6-7). The single most decisive piece of evidence is the 2.35-Å crystal structure of the S-crystallin–GSH complex by Tan et al. (2016), which demonstrated that specific active-site substitutions (Asn99→Asp101, Phe106→Gln/His108) and an 11-residue α4–α5 loop insertion have remodeled the H-site to favor GSH-mediated protein stabilization over catalysis, and that engineered "back mutations" can restore GST-like activity — proving the loss is evolutionary and specific rather than an artifact (tan2016structureofa pages 5-6, tan2016structureofa pages 4-5, tan2016structureofa pages 6-7).


Independent Family/Function Assignment

Most likely specific molecular function: Structural constituent of eye lens (GO:0005212).

Basis: OCTS1/S-crystallin 1 is a major lens protein in O. vulgaris, present at extremely high concentrations in the lens where it provides refractive properties and contributes to lens transparency through short-range order (chiou1995octopusscrystallinswith pages 4-5, tan2016structureofa pages 1-2, bergman2023illuminatingassemblydynamics pages 74-77). It retains GSH binding, but this serves a stabilization/anti-aggregation function rather than catalysis (tan2016structureofa pages 6-7, tan2016structureofa pages 5-6).

Nearest characterized homolog: Octopus hepatopancreatic GST-σ (sigma-class glutathione S-transferase), which shares ~41% sequence identity and is a catalytically active enzyme with kcat ≈ 173.6 s⁻¹ (tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 1-2).

Granularity relative to seed term: The correct GO term (GO:0005212, structural constituent of eye lens) is on a different branch from GO:0004364 (glutathione transferase activity). The seed term names the ancestral family function rather than the derived function of this specific protein. A secondary annotation of glutathione binding (GO:0043295) could be considered given the retained GSH affinity, but the catalytic MF term GO:0004364 is inappropriate for the primary annotation.


Evidence Matrix

The following table summarizes each line of evidence evaluated:

Citation (PMID/DOI) Evidence Type Supports/Refutes/Qualifies Claim Tested Key Finding Organism/Assay Context Confidence and Limitations
Chiou et al. 1995, Biochem J 309:793-800, DOI: 10.1042/BJ3090793 Direct assay; recombinant expression; comparative biochemistry Qualifies / partly refutes direct catalytic assignment Does OCTS1 directly have glutathione transferase activity? Native octopus S-crystallin showed very low GST activity, about ~0.10 µmol/min/mg versus ~100–200 µmol/min/mg for typical mammalian GSTs; recombinant protein retained activity but was about one-tenth of native S-crystallin. This shows residual GST activity, but orders-of-magnitude below bona fide GST enzymes (chiou1995octopusscrystallinswith pages 3-3, chiou1995octopusscrystallinswith pages 4-5, chiou1995octopusscrystallinswith pages 2-3). Octopus vulgaris lens S-crystallin; CDNB/GSH GST assay; native purified lens protein and recombinant expressed protein. High confidence for residual low activity; limitation: data were mostly on S-crystallin preparations/isoforms rather than a uniquely isolated OCTS1-only species, and recombinant construct/tagging/refolding likely depressed activity further.
Tan et al. 2016, Sci Rep 6:31176, DOI: 10.1038/srep31176 Crystal structure; enzyme kinetics; mutagenesis; thermal stability Refutes canonical GST-function assignment; supports activity loss/co-option Is OCTS1 an active sigma-class GST or a GST-derived crystallin with lost activity? Wild-type S-crystallin had kcat ≈ 0.24 s⁻¹ versus octopus GST-σ kcat ≈ 173.6 s⁻¹, ~700-fold lower; catalytic efficiency toward CDNB was reduced by ~6000-fold. The structure showed strong GSH binding and altered active-site architecture; engineered back-mutations restored GST-like activity, indicating evolutionary activity loss rather than absence of GST ancestry (tan2016structureofa pages 2-4, tan2016structureofa pages 6-7, tan2016structureofa pages 5-6, tan2016structureofa pages 1-2, tan2016structureofa pages 4-5, tan2016structureofa pages 7-8). Octopus vulgaris S-crystallin and octopus GST-σ; kinetic assay with GSH/CDNB; crystal structure of active mutant; mutational reconstruction. Very high confidence; strongest evidence in the set. Limitation: structural work emphasized one S-crystallin variant/mutant context, but conclusions are directly tied to the evolutionary transition of octopus lens S-crystallins.
Chuang et al. 1999, Biophys J 76:679-690, DOI: 10.1016/S0006-3495(99)77235-8 Structural/evolutionary modeling; ligand-binding comparison Refutes strong catalytic assignment; supports degenerate active site Are active-site features compatible with authentic GST catalysis? S-crystallin shares the GST fold and many G-site residues, but fails to bind S-hexylglutathione affinity resin and shows very little GST activity. Modeling identified critical substitutions (Asn99→Asp101; Phe106→His108) and an 11-residue insertion between α4 and α5 that closes/shields the active site and likely impairs catalysis and substrate access (chuang1999homologymodelingof pages 5-7, chuang1999homologymodelingof pages 1-2, chuang1999homologymodelingof pages 7-10). Cephalopod lens S-crystallin modeled against sigma-class GST template; biochemical comparison with glutathione-affinity binding behavior. High confidence for structural rationale; limitation: homology modeling rather than direct crystal structure of OCTS1 itself, though later structural work strongly corroborates the model.
Tomarev et al. 1995, J Mol Evol 41:1048-1056, DOI: 10.1007/BF00173186 Evolutionary analysis; mutagenesis in related system Qualifies / supports pseudo-enzyme interpretation Which residues distinguish active GST-σ from S-crystallin, and do S-crystallin changes explain activity loss? Y7 and W38 are essential in sigma-class GST; Y7F or W38F reduces GST activity ~50–100-fold. Additional sequence changes in S-crystallin around residues 48–50 and 101–103 plus inserted segments reduce activity several-fold to ~30-fold, supporting progressive evolutionary degeneration of catalysis during crystallin recruitment (tomarev1995glutathionestransferaseand pages 5-6). Squid/cephalopod GST and S-crystallin evolutionary comparison; mutational tests in GST/S-crystallin framework. Moderate-to-high confidence for mechanism and family-level inference; limitation: not a direct OCTS1 assay, but highly relevant for the nearest characterized homologous subfamily.
Bergman 2023 thesis, DOI: 10.17760/d20486926 Review/database compilation; comparative structural analysis Refutes direct active-GST annotation Is P27013 treated as catalytically active in recent comparative synthesis? Table entries including P27013 were flagged “N” for activity, consistent with octopus S-crystallins having lost detectable GST catalytic function while retaining the GST-derived fold/lens role (bergman2023illuminatingassemblydynamics pages 50-51, bergman2023illuminatingassemblydynamics pages 74-77). Comparative crystallin literature synthesis across cephalopods and lens proteins. Low-to-moderate confidence as secondary synthesis, not primary assay; useful as corroboration only.
Ryu et al. 2023, Front Mar Sci 10:1136602, DOI: 10.3389/fmars.2023.1136602 Developmental expression; review of prior primary literature Competing / qualifies enzymatic assignment What is the primary biological role of cephalopod S-crystallins? S-crystallins are discussed as crystallin genes recruited from GST ancestors and expressed in lens-forming tissues, supporting a primary lens-refractive/structural role rather than a detoxification-enzyme role in the eye (ryu2023eyedevelopmentand pages 11-12). Octopus minor eye development and crystallin gene expression; literature-grounded functional interpretation across cephalopods. Moderate confidence for role assignment; limitation: different species and no direct OCTS1 biochemistry.
Dominova & Zhukov 2022, Diversity 14:827, DOI: 10.3390/d14100827 Bioinformatic review/phylogenetic analysis Qualifies How should S-crystallin be placed functionally within the GST superfamily? S-crystallins are highly diverse molluscan crystallins with clear relationship to sigma-class GSTs; octopus S-crystallins are lens proteins more similar to GST than many other crystallins, but with reduced enzymatic activity, reinforcing family membership without supporting a strong direct catalytic GO annotation for each lens paralog (paper search context on Dominova 2022; no dedicated context ID-specific quantitative excerpt available beyond summary in retrieval output). Mollusc-wide sequence/phylogenetic analysis of crystallins and GST relationships. Moderate confidence for family placement; limitation: review/bioinformatic synthesis, not direct assay of OCTS1, and quantitative claims for OCTS1 are indirect.

Table: This table summarizes the main lines of evidence bearing on whether OCTS1 directly has GO:0004364 glutathione transferase activity. It contrasts direct biochemical, structural, evolutionary, and comparative evidence, highlighting that OCTS1 is GST-derived but functionally shifted toward a lens-crystallin role.

The quantitative kinetic comparison that is central to the judgment is summarized below:

Wild-type octopus S-crystallin shows Km,GSH ≈ 0.03 mM, Km,CDNB ≈ 3.9 mM, and kcat ≈ 0.24 s⁻¹, whereas authentic octopus GST-σ shows Km,GSH ≈ 1.3 mM, Km,CDNB ≈ 0.47 mM, and kcat ≈ 173.6 s⁻¹; thus S-crystallin retains very tight glutathione binding but has drastically impaired catalysis toward CDNB-like electrophilic substrates (tan2016structureofa pages 2-4).

Relative to GST-σ, S-crystallin therefore has an approximately 700-fold lower kcat and an approximately 6000-fold lower kcat/Km,CDNB, indicating that the GST-derived fold is retained but catalytic efficiency for transferase chemistry is largely lost (tan2016structureofa pages 2-4, tan2016structureofa pages 6-7).

Earlier biochemical work also found purified octopus S-crystallin to have a specific GST activity of only about 0.10 µmol/min/mg, compared with roughly 100–200 µmol/min/mg for typical mammalian GSTs, i.e. about a ~1000-fold reduction in specific activity (chiou1995octopusscrystallinswith pages 4-5).

Taken together, these data support the conclusion that OCTS1/S-crystallin is best understood as a GST-derived lens crystallin that binds GSH tightly for stability/protection, while having essentially lost canonical glutathione transferase catalytic function toward electrophilic substrates (tan2016structureofa pages 6-7, tan2016structureofa pages 5-6, tan2016structureofa pages 1-2).

Blockquote: This blockquote summarizes the key kinetic evidence comparing OCTS1/S-crystallin with authentic octopus GST-σ. It is useful because it quantifies the severe loss of catalytic efficiency while showing retention of strong glutathione binding, which is central to judging the GO function assignment.


Active-Site / Placement Analysis

A detailed residue-by-residue comparison of the active site between octopus GST-σ and OCTS1 S-crystallin reveals the structural basis for loss of catalytic function:

Position in GST-σ Residue in GST-σ Position in S-crystallin (OCTS1) Residue in S-crystallin Status (Conserved/Substituted) Functional Impact
7 Tyr 8 Tyr Conserved Catalytic Tyr retained; proposed general base that lowers the pKa of the GSH thiol, so catalytic loss is not explained by loss of this residue alone (tomarev1995glutathionestransferaseand pages 5-6, chuang1999homologymodelingof pages 7-10)
13 Arg 14 Arg Conserved/perturbed Arg retained, but in S-crystallin its catalytic role is weakened by nearby Asp101, which alters charge interactions and destabilizes optimal Meisenheimer-complex stabilization (tan2016structureofa pages 4-5, tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 7-10)
38 Trp 39 Trp Conserved Essential GSH-binding residue retained; supports preservation of G-site/GSH affinity despite loss of efficient transferase catalysis (tomarev1995glutathionestransferaseand pages 5-6, chuang1999homologymodelingof pages 5-7)
42 Lys 43 Arg Conservative substitution G-site residue remains basic; little predicted effect compared with major H-site changes (chuang1999homologymodelingof pages 5-7)
48 Asn 49 Ser Substituted G-site altered at one contact position; contributes modestly to changed GSH-binding geometry but is not the main cause of activity loss (chuang1999homologymodelingof pages 5-7)
62/64 Asn 64 Asn Conserved Conserved GSH-binding residue; consistent with strong GSH affinity in S-crystallin (chuang1999homologymodelingof pages 5-7, tan2016structureofa pages 1-2)
63 Ser 65 Ser Conserved Conserved GSH-binding residue; supports intact G-site chemistry for ligand binding (chuang1999homologymodelingof pages 5-7, tan2016structureofa pages 1-2)
50 Met 51 Met Conserved Conserved G-site contact; supports preservation of glutathione binding rather than efficient xenobiotic conjugation (chuang1999homologymodelingof pages 5-7, tan2016structureofa pages 1-2)
98 Phe 100 Leu Substituted Aromatic H-site residue replaced by smaller aliphatic residue, helping collapse/reshape the hydrophobic substrate-binding pocket and weakening binding of aromatic electrophiles such as CDNB (tan2016structureofa pages 2-4, tan2016structureofa pages 5-6)
99 Asn 101 Asp Critical substitution Charge reversal near Arg14; alters positive environment needed to stabilize the negatively charged Meisenheimer intermediate and is a key mechanistic explanation for reduced GST catalysis (tan2016structureofa pages 4-5, tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 1-2, chuang1999homologymodelingof pages 7-10)
102 Val 104 Met Substituted Alters H-site hydrophobic pocket geometry and contributes to poor electrophilic substrate accommodation (tan2016structureofa pages 4-5, tan2016structureofa pages 2-4, tan2016structureofa pages 5-6)
106 Phe 108 Gln/His Critical substitution Aromatic hydrophobic residue replaced by polar residue in native S-crystallin; strongly disrupts H-site architecture. Q108F back-mutation partially restores GST-like activity, showing this site is functionally decisive (tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 1-2, tan2016structureofa pages 1-2, tan2016structureofa pages 5-6)
α4-α5 region No long insertion 112-122 11-residue insertion including Cys112 Insertional divergence Long loop occludes access to the active site and promotes high-affinity GSH binding; Cys112 can form a disulfide with bound GSH. This favors stabilization/structural function over catalysis (tan2016structureofa pages 4-5, tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 1-2, tan2016structureofa pages 1-2)
Summary G-site largely intact OCTS1 active site overall G-site conserved, H-site remodeled Qualifying summary OCTS1 preserves many canonical GSH-binding residues, explaining strong GSH binding, but has multiple H-site substitutions plus the α4-α5 loop insertion that block/reshape substrate access and collapse catalytic competence; this pattern is consistent with a GST-derived pseudo-enzyme adapted as a lens crystallin (tan2016structureofa pages 2-4, tan2016structureofa pages 5-6, chuang1999homologymodelingof pages 5-7, chuang1999homologymodelingof pages 7-10)

Table: This table compares key catalytic and binding residues between authentic octopus GST-σ and OCTS1 S-crystallin. It highlights that the glutathione-binding G-site is mostly retained, whereas H-site substitutions and a loop insertion explain the major loss of glutathione transferase activity.

Summary of active-site status: The catalytic Tyr8 (general base) is conserved, as are several G-site (glutathione-binding) residues including Trp39, Asn64, and Ser65, explaining the tight GSH binding (Km,GSH ≈ 0.03 mM, tighter than GST-σ's 1.3 mM) (tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 5-7, tan2016structureofa pages 1-2). However, the catalytic residues are NOT functionally intact because: (1) the Asn99→Asp101 charge-reversal substitution places a negative charge adjacent to Arg14, disrupting stabilization of the negatively charged Meisenheimer complex intermediate essential for GST catalysis (tan2016structureofa pages 2-4, chuang1999homologymodelingof pages 1-2, chuang1999homologymodelingof pages 7-10); (2) the H-site hydrophobic substrate-binding pocket is collapsed by Phe98→Leu100, Val102→Met104, and Phe106→Gln/His108 substitutions (tan2016structureofa pages 4-5, tan2016structureofa pages 2-4, tan2016structureofa pages 5-6); and (3) an 11-residue insertion between helices α4 and α5 (residues 112–122), including Cys112 that forms a disulfide with bound GSH, further occludes the active site (chuang1999homologymodelingof pages 1-2, tan2016structureofa pages 1-2).

This pattern — conserved fold, conserved GSH-binding site, degenerate electrophilic substrate-binding and catalytic machinery — is the hallmark of an enzyme-derived structural protein (pseudo-enzyme). Reverse-engineering experiments confirmed this: the quadruple mutant L100F/D101N/M104V/Q108F in S-crystallin restored ~100-fold higher GST activity, while the reciprocal GST-to-S-crystallin conversion (F98L/N99D/V102M/F106Q plus loop insertion) reduced GST activity by ~120-fold (tan2016structureofa pages 5-6, tan2016structureofa pages 4-5).


GO Curation Implications

Recommended curation action: Remove GO:0004364 and replace with GO:0005212 (structural constituent of eye lens).

The rationale is as follows:

  1. Remove GO:0004364 (glutathione transferase activity): The ~700–6,000-fold reduction in catalytic parameters, combined with structural evidence of active-site remodeling, means this protein does not function as a glutathione transferase in its biological context. A conserved fold with a degenerate active site does not support a catalytic MF term (tan2016structureofa pages 2-4, tan2016structureofa pages 6-7, chuang1999homologymodelingof pages 1-2).

  2. Assign GO:0005212 (structural constituent of eye lens): OCTS1 is the major soluble protein of the octopus lens, present at concentrations required for refractive index generation and lens transparency. Multiple independent studies confirm its primary role as a lens crystallin (tan2016structureofa pages 6-7, chiou1995octopusscrystallinswith pages 4-5, tan2016structureofa pages 1-2, ryu2023eyedevelopmentand pages 11-12, bergman2023illuminatingassemblydynamics pages 74-77).

  3. Consider GO:0043295 (glutathione binding) as secondary annotation: S-crystallin retains strong GSH affinity (Km ≈ 0.03 mM), and GSH binding serves a physiologically relevant stabilization/anti-aggregation function in the lens (tan2016structureofa pages 2-4, tan2016structureofa pages 5-6, tan2016structureofa pages 6-7). This would capture the retained binding function without implying catalysis.

  4. Do not assign "protein binding" as a fallback — the specific structural/lens function and GSH-binding function are more informative.

This case should also be flagged as a potential systematic issue for PANTHER TreeGrafter: the GST family tree likely includes both authentic GST enzymes and S-crystallin lens proteins in its cephalopod branches, and the pipeline may not distinguish between catalytically active vs. co-opted members at this node.


Conflicts, Knowledge Gaps, and Discriminating Tests

Conflicts and Nuances

Knowledge Gaps

  1. No isoform-specific kinetic data for OctS1 (P27013) alone have been published; existing kinetic data are from S-crystallin preparations containing a mixture of isoforms or from OctS4-based constructs.
  2. Direct AlphaFold or experimental structure of OctS1 specifically (as opposed to OctS4 Q108F mutant) has not been reported.
  3. Whether the trace GST activity contributes meaningfully to lens antioxidant defense at the very high protein concentrations found in the lens has not been conclusively resolved.

Most Efficient Discriminating Tests

  1. Isoform-specific kinetics: Express and purify recombinant OctS1 alone and measure kcat/Km for CDNB–GSH conjugation directly. This would definitively resolve whether OctS1 has even less activity than the S-crystallin preparations studied.
  2. Isoform-specific crystal structure: Solve the structure of wild-type OctS1 to confirm the predicted H-site remodeling and loop conformation specific to this isoform.
  3. In vivo knockout/knockdown: If OCTS1 loss affects only lens refractive properties (not detoxification/xenobiotic metabolism), it would confirm a purely structural role.
  4. Mass spectrometry of GSH conjugates in lens: Test whether GST-dependent conjugation products accumulate in octopus lens tissue, which would indicate biologically relevant catalytic activity in situ.

References

  1. (tan2016structureofa pages 2-4): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

  2. (tan2016structureofa pages 6-7): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

  3. (tan2016structureofa pages 5-6): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

  4. (tan2016structureofa pages 4-5): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

  5. (chiou1995octopusscrystallinswith pages 4-5): S. Chiou, C. W. Yu, C. W. Lin, F. Pan, S. F. Lu, H. Lee, and G. Chang. Octopus s-crystallins with endogenous glutathione s-transferase (gst) activity: sequence comparison and evolutionary relationships with authentic gst enzymes. The Biochemical journal, 309 ( Pt 3):793-800, Aug 1995. URL: https://doi.org/10.1042/bj3090793, doi:10.1042/bj3090793. This article has 22 citations.

  6. (tan2016structureofa pages 1-2): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

  7. (bergman2023illuminatingassemblydynamics pages 74-77): Michael Richard Bergman. Illuminating assembly dynamics regulating short-range order optics in extremely long-lived proteins. ArXiv, 2023. URL: https://doi.org/10.17760/d20486926, doi:10.17760/d20486926. This article has 0 citations.

  8. (chuang1999homologymodelingof pages 1-2): Chyh-Chong Chuang, Shih-Hsiung Wu, Shyh-Horng Chiou, and Gu-Gang Chang. Homology modeling of cephalopod lens s-crystallin: a natural mutant of sigma-class glutathione transferase with diminished endogenous activity. Biophysical journal, 76 2:679-90, Feb 1999. URL: https://doi.org/10.1016/s0006-3495(99)77235-8, doi:10.1016/s0006-3495(99)77235-8. This article has 27 citations and is from a domain leading peer-reviewed journal.

  9. (chiou1995octopusscrystallinswith pages 3-3): S. Chiou, C. W. Yu, C. W. Lin, F. Pan, S. F. Lu, H. Lee, and G. Chang. Octopus s-crystallins with endogenous glutathione s-transferase (gst) activity: sequence comparison and evolutionary relationships with authentic gst enzymes. The Biochemical journal, 309 ( Pt 3):793-800, Aug 1995. URL: https://doi.org/10.1042/bj3090793, doi:10.1042/bj3090793. This article has 22 citations.

  10. (chiou1995octopusscrystallinswith pages 2-3): S. Chiou, C. W. Yu, C. W. Lin, F. Pan, S. F. Lu, H. Lee, and G. Chang. Octopus s-crystallins with endogenous glutathione s-transferase (gst) activity: sequence comparison and evolutionary relationships with authentic gst enzymes. The Biochemical journal, 309 ( Pt 3):793-800, Aug 1995. URL: https://doi.org/10.1042/bj3090793, doi:10.1042/bj3090793. This article has 22 citations.

  11. (tan2016structureofa pages 7-8): Wei-Hung Tan, Shu-Chun Cheng, Yu-Tung Liu, Cheng-Guo Wu, Min-Han Lin, Chiao-Che Chen, Chao-Hsiung Lin, and Chi-Yuan Chou. Structure of a highly active cephalopod s-crystallin mutant: new molecular evidence for evolution from an active enzyme into lens-refractive protein. Scientific Reports, Aug 2016. URL: https://doi.org/10.1038/srep31176, doi:10.1038/srep31176. This article has 17 citations and is from a peer-reviewed journal.

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