LYS-1 is one of the protist-type (Entamoeba-type) lysozymes of Caenorhabditis elegans, a nematode that carries an unusually large and divergent lysozyme family (15 genes split into protist-type lys and invertebrate-type ilys classes). Structurally it is a glycoside hydrolase family 25 (GH25) protein with an N-terminal signal peptide. LYS-1 functions as an infection-inducible antibacterial effector of the intestinal innate immune response: it is one of the most strongly induced genes upon infection by the Gram-negative bacterium Serratia marcescens, and its overexpression increases resistance to that pathogen, while RNAi knockdown reduces survival on the Gram-positive bacterium Staphylococcus aureus. It is also transcriptionally upregulated by Bacillus thuringiensis and is part of the ELT-2/GATA-controlled intestinal infection-response program, and it is a DAF-16/FOXO target that links the immune response to the dauer developmental decision. The protein localizes to vesicles in the apical region of intestinal cells and is expressed in the intestine and a subset of head neurons. Although the GH25 fold implies muramidase (peptidoglycan-hydrolysing) activity, this catalytic activity has never been demonstrated for LYS-1 at the protein level, and the sequence lacks the conserved active-site residues, so its actual enzymatic function is uncertain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0007165 signal transduction | IBA GO_REF:0000033 | REMOVE | Summary: This IBA is a phylogenetic propagation from a PANTHER subfamily seeded by non-lysozyme members (including a Dictyostelium protein). Lysozymes are secreted antibacterial hydrolases/effectors, not signal-transducing proteins, and there is no evidence that LYS-1 transduces any signal. Reason: Over-broad phylogenetic inference inconsistent with the biology of a lysozyme-family antibacterial effector. No experimental or sequence feature supports a signal transduction role for LYS-1; the specific, experimentally supported role is antibacterial defense (captured by the defense-response terms below). Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE GRANULARITY MISMATCH Sources checked: PANTHER:PTN000574946 · PTN000574946 (PANTHER ancestral node) SOURCE WEAK OR INFERRED Ancestral node whose GO:0007165 assignment was seeded from dictyBase:DDB_G0273175 (a Dictyostelium protein). "Signal transduction" is not a function of a GH25 lysozyme-family antibacterial effector; the propagation transfers an unrelated, overly generic process to LYS-1. |
| GO:0045087 innate immune response | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The innate-immune-response assignment is correct for LYS-1, but this IBA is redundant with the stronger experimental IMP (PMID:21209831) and HEP (PMID:16968778) annotations to the same term. Retained as valid biological process context rather than as a distinct line of evidence. Reason: Correct process but redundant with experimental annotations to the same term; the more specific defense-response-to-Gram-positive/Gram-negative terms carry the core biology. |
| GO:0003796 lysozyme activity | IEA GO_REF:0000002 | UNDECIDED | Summary: This is a family/domain-based (InterPro IPR002053, GH25) inference of muramidase activity. It has never been demonstrated for LYS-1: no C. elegans lysozyme has been characterized at the protein level, and UniProt flags a CAUTION that LYS-1 "Lacks conserved active site residues, suggesting it has no catalytic activity." The activity therefore cannot be confirmed, and there is positive sequence evidence that it may be absent. Reason: Cannot verify: no biochemical/enzymatic assay of purified LYS-1 exists, and the UniProt active-site CAUTION suggests possible loss of catalytic activity. Per guidelines this is an author-flagged unresolved MF, not a confident REMOVE (family activity cannot be definitively excluded without biochemistry). This is the central molecular-function knowledge gap for this gene. Supporting Evidence: PMID:21931778 All available data is based on genetic analysis, whereas none of the lysozymes have been characterized at the protein level. |
| GO:0006950 response to stress | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: A very generic ARBA machine-learned assignment. The specific infection/defense-response terms below describe LYS-1's biology far more informatively; a bare response-to-stress term adds little. Reason: Too general to be informative and subsumed by the specific defense response / innate immune response annotations that are experimentally supported. |
| GO:0009253 peptidoglycan catabolic process | IEA GO_REF:0000002 | UNDECIDED | Summary: The biological-process counterpart of the unverified lysozyme activity (InterPro/GH25 inference). Because peptidoglycan hydrolysis by LYS-1 has not been demonstrated and the sequence may lack catalytic residues, this process cannot be confirmed for this paralog. Reason: Depends on an unverified catalytic (muramidase) activity; no direct evidence LYS-1 cleaves peptidoglycan. Tied to the lysozyme-activity knowledge gap. Supporting Evidence: PMID:21931778 All available data is based on genetic analysis, whereas none of the lysozymes have been characterized at the protein level. |
| GO:0016998 cell wall macromolecule catabolic process | IEA GO_REF:0000002 | UNDECIDED | Summary: A more general parent of peptidoglycan catabolism, from the same family-based InterPro inference; same caveat that the underlying catalytic activity is undemonstrated for LYS-1. Reason: Same unverified-catalysis basis as the peptidoglycan/lysozyme-activity annotations; cannot confirm cell-wall macromolecule catabolism for LYS-1. |
| GO:0060205 cytoplasmic vesicle lumen | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt Subcellular Location keyword propagation matching the curated localization of LYS-1 to the lumen of apical intestinal vesicles. Redundant with the EXP annotation from PMID:12176330. Reason: Correct location but electronically propagated and redundant with the experimental EXP/IDA vesicle annotations. |
| GO:0060205 cytoplasmic vesicle lumen | EXP PMID:12176330 Inducible antibacterial defense system in C. elegans. | ACCEPT | Summary: Experimentally curated localization of LYS-1 to the lumen of vesicles in the apical region of intestinal cells, from the primary characterization of the inducible antibacterial defense system. Reason: Curator-assigned experimental localization consistent with a secreted intestinal antibacterial effector stored in apical vesicles. |
| GO:0045087 innate immune response | HEP PMID:16968778 A conserved role for a GATA transcription factor in regulati... | KEEP AS NON CORE | Summary: High-throughput expression evidence: lys-1 is part of the intestinal ELT-2/GATA-regulated infection-response gene program identified in a genome-wide study of epithelial innate immunity. Consistent with its infection-inducible antibacterial role. Reason: Expression-based support for involvement in the innate immune response; corroborates the experimental IMP annotation but is itself expression- level evidence. |
| GO:0045087 innate immune response | IMP PMID:21209831 RNAi screen of DAF-16/FOXO target genes in C. elegans links ... | ACCEPT | Summary: RNAi knockdown of lys-1 significantly reduces C. elegans survival on the pathogen Staphylococcus aureus (TD50 4.7 vs 6.8 days for control, p<0.0001), demonstrating that lys-1 is required for a normal innate immune/pathogen-resistance response. Reason: Direct loss-of-function (RNAi) phenotype establishing a functional role in the innate immune response; core immune-defense biology of the gene. Supporting Evidence: PMID:21209831 Two genes, lys-1 and clc-1, were required for normal resistance to S. aureus. |
| GO:0050830 defense response to Gram-positive bacterium | IMP PMID:21209831 RNAi screen of DAF-16/FOXO target genes in C. elegans links ... | ACCEPT | Summary: Staphylococcus aureus is a Gram-positive bacterium, and lys-1 RNAi reduces survival on it (TD50 4.7 vs 6.8 days, p<0.0001), directly supporting a role in defense against Gram-positive bacteria. This is the most specific, experimentally supported process term for the gene. Reason: Specific, experimentally demonstrated defense function against a Gram-positive pathogen; a core biological process of LYS-1. Supporting Evidence: PMID:21209831 The TD50 (time required for 50% of the nematodes to die) for lys-1 was 4.7 days (p<0.0001) |
| GO:0031410 cytoplasmic vesicle | IDA PMID:12176330 Inducible antibacterial defense system in C. elegans. | ACCEPT | Summary: Direct-assay localization of LYS-1 to cytoplasmic vesicles in intestinal cells, from the primary characterization paper. Reason: Experimentally observed subcellular localization consistent with storage of the effector in intestinal vesicles. |
| GO:0045177 apical part of cell | IDA PMID:12176330 Inducible antibacterial defense system in C. elegans. | ACCEPT | Summary: LYS-1 localizes to the apical region of intestinal cells (apically positioned vesicles), consistent with secretion toward the gut lumen where ingested bacteria are encountered. Reason: Experimentally supported apical localization appropriate for a gut-luminal antibacterial effector. |
| GO:0050829 defense response to Gram-negative bacterium | IEP PMID:12176330 Inducible antibacterial defense system in C. elegans. | ACCEPT | Summary: lys-1 is among the most robustly induced genes upon infection by the Gram-negative bacterium Serratia marcescens, and its overexpression augments resistance to that pathogen, supporting a role in defense against Gram-negative bacteria. The evidence code is IEP (expression), reinforced by the overexpression gain-of-resistance phenotype. Reason: Infection-inducible expression plus overexpression-conferred resistance establish a defense role against a Gram-negative pathogen; a core biological process of LYS-1. Supporting Evidence: PMID:12176330 overexpression of the lysozyme gene lys-1 augments the resistance of C. elegans to S. marcescens. |
Loading supporting content…
Download this section (compressed HTML)Q: Does purified LYS-1 protein possess muramidase/bacteriolytic activity, or has this GH25 protist-type lysozyme lost catalytic function and act by a non-enzymatic antibacterial mechanism?
Suggested experts: Schulenburg H
Q: What is the phenotype of a lys-1 loss-of-function null, and to what extent is lys-1 redundant with other protist-type lysozymes in defense against ingested pathogens?
Suggested experts: Schulenburg H, Ewbank JJ
Experiment: Express and purify recombinant LYS-1, then assay (i) muramidase activity on Micrococcus luteus cell walls and defined peptidoglycan substrates, (ii) bacteriolytic/growth-inhibitory activity against S. aureus and S. marcescens, and (iii) direct binding to bacterial cell-surface components; pair with active-site mutagenesis and, if possible, structure determination.
Hypothesis: LYS-1 either hydrolyzes bacterial peptidoglycan (canonical lysozyme mechanism) or, lacking active-site residues, kills/inhibits bacteria by a non-catalytic binding/permeabilizing mechanism.
Type: biochemistry / enzymology / structural biology
Experiment: Generate a lys-1 null allele (CRISPR) and test survival and intestinal pathogen load on a panel of Gram-negative and Gram-positive pathogens (S. marcescens, S. aureus, B. thuringiensis, P. aeruginosa), comparing single mutant, paralog combinations, and rescue/overexpression lines.
Hypothesis: lys-1 contributes non-redundantly to intestinal antibacterial defense in vivo.
Type: genetics / host-pathogen survival and CFU assays
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: It is not known whether LYS-1 has any muramidase / lysozyme (peptidoglycan-hydrolysing) enzymatic activity. All functional evidence is genetic (infection-inducible expression, RNAi, overexpression); the protein has never been purified or assayed, and its sequence lacks the conserved GH25 active-site residues, raising the possibility that it is a pseudo-muramidase.
OPEN BIOLOGY MF_DARK
What is known: What is firmly established is that LYS-1 is a GH25 protist-type lysozyme whose gene is infection-inducible and functionally required for normal antibacterial defense (S. marcescens, S. aureus). What is unknown is the biochemical activity of the protein: whether it cleaves peptidoglycan, permeabilizes/agglutinates bacteria by another mechanism, or acts non-catalytically.
Significance: Whether LYS-1 kills bacteria enzymatically (like canonical lysozymes) or by a non-catalytic mechanism determines the correct molecular-function annotation and whether the current InterPro-based lysozyme-activity / peptidoglycan-catabolism annotations should stand. This is a recurring issue across the expanded, divergent C. elegans lysozyme family.
What would resolve it: Express and purify recombinant LYS-1 and assay muramidase / bacteriolytic activity (e.g. on Micrococcus cell walls and defined peptidoglycan) and its ability to bind/permeabilize target bacteria; complement with active-site residue mutagenesis and structural analysis.
Provenance (the field's own admissions):
Gap: The molecular substrate or microbial target of LYS-1 is undefined: it is unknown which bacterial surface molecule(s) LYS-1 acts on, and whether its antibacterial spectrum extends beyond S. marcescens, S. aureus and B. thuringiensis.
OPEN BIOLOGY MF_DARK
What is known: LYS-1 is known to be required for resistance to S. aureus and to protect against S. marcescens when overexpressed, and it is transcriptionally induced by these plus B. thuringiensis. What is unknown is the direct biochemical target/substrate and the full microbial spectrum.
Significance: Identifying the target molecule would clarify the mechanism (enzymatic versus binding/permeabilizing) and the range of pathogens LYS-1 counters, informing both its MF annotation and its place in the surveillance-immunity effector repertoire.
What would resolve it: Biochemical target/substrate identification with purified protein (peptidoglycan/cell-wall degradation assays, pull-downs of bacterial ligands) and broader pathogen-panel survival/CFU assays with defined lys-1 loss- and gain-of-function strains.
Provenance (the field's own admissions):
Gap: Whether lys-1 is individually necessary in vivo or is functionally redundant within the 15-member C. elegans lysozyme family is unresolved. The defense phenotypes rest on RNAi knockdown and overexpression rather than a characterized single-gene null, and many lysozyme paralogs share overlapping infection-induction profiles.
OPEN BIOLOGY BP_DARK
What is known: lys-1 RNAi reduces S. aureus survival and lys-1 overexpression increases S. marcescens resistance, establishing a contribution to defense. What is unknown is the phenotype of a clean lys-1 loss-of-function null and the degree of redundancy with paralogs such as lys-2, lys-3 and lys-7.
Significance: Redundancy determines whether lys-1 is a non-redundant defense gene or one of several partially interchangeable effectors, which affects how strongly its individual loss impacts host survival and how its biological role should be weighted.
What would resolve it: Generate and phenotype a lys-1 null allele (and higher-order lysozyme combinatorial mutants) across a pathogen panel, quantifying survival and pathogen load relative to wild type and to single-paralog mutants.
Provenance (the field's own admissions):
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)