CHS7

UniProt ID: P38843
Organism: Saccharomyces cerevisiae
Review Status: COMPLETE
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Gene Description

CHS7 encodes an endoplasmic-reticulum membrane export chaperone for the chitin synthase Chs3, promoting Chs3 folding/proteostasis, ER-to-Golgi export, and normal chitin synthase III-dependent cell wall chitin deposition.

Proposed New Ontology Terms

chitin synthase export chaperone activity

Definition: A protein folding chaperone activity that binds or escorts a chitin synthase client in the endoplasmic reticulum to promote its productive folding, ER quality-control evasion, and export toward the Golgi.

Justification: Chs7 is not a generic unfolded-protein binder; the yeast evidence supports a dedicated export-chaperone activity for Chs3/chitin synthase III that is more specific than existing chaperone terms. The 2023 Sanchez et al. MBoC study strengthens this by showing that Chs7 also functions as a degron shield, masking Chs3 cytosolic degrons to prevent ERAD-C targeting.

Parent term: protein folding chaperone

Supporting Evidence:

Existing Annotations Review

GO Term Evidence Action Reason
GO:0006031 chitin biosynthetic process
IBA
GO_REF:0000033 		ACCEPT
Summary: chitin biosynthetic process reviewed for CHS7: ACCEPT.
Reason: Retain as a core biological-process consequence of Chs7-dependent Chs3 maturation and export; loss of CHS7 strongly reduces chitin synthase III output and cell wall chitin deposition.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Loss of CHS7 causes **ER retention of Chs3**, severe reduction of **cell wall chitin** and **CSIII activity**
GO:0005789 endoplasmic reticulum membrane
IBA
GO_REF:0000033 		ACCEPT
Summary: endoplasmic reticulum membrane reviewed for CHS7: ACCEPT.
Reason: Retain as the best-supported cellular location; Chs7 is a multipass ER membrane protein acting at the Chs3 ER export step.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
functional tagged Chs7 showed **perinuclear/ER localization** and co-localization with the ER marker Sec63p
GO:0006457 protein folding
IBA
GO_REF:0000033 		ACCEPT
Summary: protein folding reviewed for CHS7: ACCEPT.
Reason: Retain because Chs7 functions in client folding/proteostasis of the polytopic Chs3 cargo, even though the more specific role is a dedicated export chaperone.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
describe Chs7 as a **specific ER chaperone** that prevents Chs3 aggregation and promotes ER exit via **COPII loading**
GO:0051082 unfolded protein binding
IBA
GO_REF:0000033 		MODIFY
Summary: unfolded protein binding reviewed for CHS7: MODIFY.
Reason: The generic unfolded-protein binding term is less informative than the supported Chs3-specific chaperone/escort role; replace with protein folding chaperone.
Proposed replacements: protein folding chaperone
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 is an export chaperone in the sense that **Chs3 ER exit depends on Chs7**
GO:0005789 endoplasmic reticulum membrane
IEA
GO_REF:0000044 		ACCEPT
Summary: endoplasmic reticulum membrane reviewed for CHS7: ACCEPT.
Reason: Retain as the best-supported cellular location; Chs7 is a multipass ER membrane protein acting at the Chs3 ER export step.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
functional tagged Chs7 showed **perinuclear/ER localization** and co-localization with the ER marker Sec63p
GO:0015031 protein transport
IEA
GO_REF:0000043 		MODIFY
Summary: protein transport reviewed for CHS7: MODIFY.
Reason: General protein transport is too broad for the curated evidence; Chs7 specifically promotes Chs3 exit from the ER toward the Golgi.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 is required for exit of Chs3 from the ER
GO:0071555 cell wall organization
IEA
GO_REF:0000043 		KEEP AS NON CORE
Summary: cell wall organization reviewed for CHS7: KEEP_AS_NON_CORE.
Reason: Keep as a valid downstream phenotype of impaired Chs3-dependent chitin deposition, but not the direct molecular role of Chs7.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
These quantitative data support the central functional claim that CHS7 is required for normal Chs3/CSIII-dependent chitin deposition
GO:0005515 protein binding
IPI
PMID:18467557
An in vivo map of the yeast protein interactome. 		MARK AS OVER ANNOTATED
Summary: protein binding reviewed for CHS7: MARK_AS_OVER_ANNOTATED.
Reason: Protein binding is too generic; the Chs3 interaction is better captured by a specific chaperone/export role.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 **physically interacts** with full-length Chs3 and certain truncated Chs3 forms
GO:0005515 protein binding
IPI
PMID:37968396
The social and structural architecture of the yeast protein ... 		MARK AS OVER ANNOTATED
Summary: protein binding reviewed for CHS7: MARK_AS_OVER_ANNOTATED.
Reason: Protein binding is too generic; the Chs3 interaction is better captured by a specific chaperone/export role.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 **physically interacts** with full-length Chs3 and certain truncated Chs3 forms
GO:0005783 endoplasmic reticulum
HDA
PMID:22842922
Dissecting DNA damage response pathways by analysing protein... 		ACCEPT
Summary: endoplasmic reticulum reviewed for CHS7: ACCEPT.
Reason: Retain as a supported broader ER localization, consistent with the more precise ER membrane annotation.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
functional tagged Chs7 showed **perinuclear/ER localization** and co-localization with the ER marker Sec63p
GO:0005783 endoplasmic reticulum
HDA
PMID:26928762
One library to make them all: streamlining the creation of y... 		ACCEPT
Summary: endoplasmic reticulum reviewed for CHS7: ACCEPT.
Reason: Retain as a supported broader ER localization, consistent with the more precise ER membrane annotation.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
functional tagged Chs7 showed **perinuclear/ER localization** and co-localization with the ER marker Sec63p
GO:0005934 cellular bud tip
HDA
PMID:22842922
Dissecting DNA damage response pathways by analysing protein... 		KEEP AS NON CORE
Summary: cellular bud tip reviewed for CHS7: KEEP_AS_NON_CORE.
Reason: Keep as context-dependent localization associated with Chs3/chitin deposition biology, not as the primary site of Chs7 action.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 can also **exit the ER with Chs3** and co-localize with Chs3 at the bud neck and intracellular puncta
GO:0005935 cellular bud neck
HDA
PMID:22842922
Dissecting DNA damage response pathways by analysing protein... 		KEEP AS NON CORE
Summary: cellular bud neck reviewed for CHS7: KEEP_AS_NON_CORE.
Reason: Keep as context-dependent bud-neck localization associated with chitin deposition, not as the core ER export role.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 can also **exit the ER with Chs3** and co-localize with Chs3 at the bud neck and intracellular puncta
GO:0005628 prospore membrane
HDA
PMID:24390141
A visual screen of protein localization during sporulation i... 		KEEP AS NON CORE
Summary: prospore membrane reviewed for CHS7: KEEP_AS_NON_CORE.
Reason: Keep as a sporulation-context localization observation, peripheral to the core ER chaperone/export function.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Reported induction includes **~24-fold during sporulation**
GO:0005935 cellular bud neck
IDA
PMID:29405545
The chaperone Chs7 forms a stable complex with Chs3 and prom... 		KEEP AS NON CORE
Summary: cellular bud neck reviewed for CHS7: KEEP_AS_NON_CORE.
Reason: Keep as context-dependent bud-neck localization associated with chitin deposition, not as the core ER export role.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 can also **exit the ER with Chs3** and co-localize with Chs3 at the bud neck and intracellular puncta
GO:0005789 endoplasmic reticulum membrane
IDA
PMID:10366589
Chs7p, a new protein involved in the control of protein expo... 		ACCEPT
Summary: endoplasmic reticulum membrane reviewed for CHS7: ACCEPT.
Reason: Retain as the best-supported cellular location; Chs7 is a multipass ER membrane protein acting at the Chs3 ER export step.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
functional tagged Chs7 showed **perinuclear/ER localization** and co-localization with the ER marker Sec63p
GO:0006031 chitin biosynthetic process
IMP
PMID:10366589
Chs7p, a new protein involved in the control of protein expo... 		ACCEPT
Summary: chitin biosynthetic process reviewed for CHS7: ACCEPT.
Reason: Retain as a core biological-process consequence of Chs7-dependent Chs3 maturation and export; loss of CHS7 strongly reduces chitin synthase III output and cell wall chitin deposition.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Loss of CHS7 causes **ER retention of Chs3**, severe reduction of **cell wall chitin** and **CSIII activity**
GO:0006457 protein folding
IMP
PMID:15623581
Specialized membrane-localized chaperones prevent aggregatio... 		ACCEPT
Summary: protein folding reviewed for CHS7: ACCEPT.
Reason: Retain because Chs7 functions in client folding/proteostasis of the polytopic Chs3 cargo, even though the more specific role is a dedicated export chaperone.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
describe Chs7 as a **specific ER chaperone** that prevents Chs3 aggregation and promotes ER exit via **COPII loading**
GO:0006888 endoplasmic reticulum to Golgi vesicle-mediated transport
IDA
PMID:10366589
Chs7p, a new protein involved in the control of protein expo... 		ACCEPT
Summary: endoplasmic reticulum to Golgi vesicle-mediated transport reviewed for CHS7: ACCEPT.
Reason: Retain as a core process: the strongest mechanistic evidence places Chs7 at Chs3 ER exit and ER-to-Golgi trafficking.
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
Chs7 is an export chaperone in the sense that **Chs3 ER exit depends on Chs7**
GO:0051082 unfolded protein binding
IMP
PMID:15623581
Specialized membrane-localized chaperones prevent aggregatio... 		MODIFY
Summary: unfolded protein binding reviewed for CHS7: MODIFY.
Reason: The generic unfolded-protein binding term is less informative than the supported Chs3-specific chaperone/escort role; replace with protein folding chaperone.
Proposed replacements: protein folding chaperone
Supporting Evidence:
file:yeast/CHS7/CHS7-deep-research-falcon.md
describe Chs7 as a **specific ER chaperone** that prevents Chs3 aggregation and promotes ER exit via **COPII loading**

Core Functions

Chs7 acts as a client-specific ER membrane chaperone/escort for Chs3, licensing productive Chs3 biogenesis and export rather than acting as the chitin synthase enzyme itself.

Molecular Function:
protein folding chaperone
Directly Involved In:
endoplasmic reticulum to Golgi vesicle-mediated transport chitin biosynthetic process
Cellular Locations:
endoplasmic reticulum membrane
Supporting Evidence:
  • file:yeast/CHS7/CHS7-deep-research-falcon.md
    Chs7 acts at the earliest licensing step for the Chs3 trafficking itinerary

References

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Suggested Questions for Experts

Q: Does Chs7 have physiologically important clients other than Chs3, or is its conserved role essentially dedicated to chitin synthase export?

Q: Which Chs3 surfaces are shielded by Chs7 during ER quality control and ERAD avoidance?

Suggested Experiments

Experiment: Map Chs3 regions that require Chs7 using endogenous tagged Chs3 truncation or degron mutants, ER export assays, co-immunoprecipitation, and ERAD/INMAD pathway perturbations.

Hypothesis: Chs7 promotes Chs3 ER export by masking Chs3 degrons while maintaining an export-competent conformation.

Type: client-mapping and trafficking assay

Deep Research

Falcon

(CHS7-deep-research-falcon.md)

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