CpaA (SAUSA300_0911) is a Staphylococcus aureus USA300 membrane cation/proton antiporter with cytoplasmic RCK regulatory domains. Its RCK_C domain binds cyclic di-AMP, and reconstituted full-length protein shows nucleotide-dependent alteration of antiporter activity. The transported cation selectivity and physiological direction of this modulation require more specific assay evidence than the accessible primary abstract provides.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006812 monoatomic cation transport | IEA GO_REF:0000002 | ACCEPT | Summary: CpaA transports monovalent cations as an antiporter. Reason: The CPA2 architecture and the full-length proteoliposome transport assay support cation transport. The currently accessible assay summary does not justify a narrower cation assignment. Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. PMID:23671116 a predicted cation/proton antiporter, CpaA, which as we show here also directly binds c-di-AMP. |
| GO:0006813 potassium ion transport | IEA GO_REF:0000002 | UNDECIDED | Summary: The potassium-specific transport assignment remains unresolved in the accessible primary evidence. Reason: The source maps a transport-family feature to potassium transport. PMID:26171638 confirms antiporter activity but its accessible abstract does not identify the transported cation; the full text was inaccessible. Retain uncertainty rather than claiming potassium exclusion or promoting a secondary-source interpretation to a direct assay. Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:0008324 monoatomic cation transmembrane transporter activity | IEA GO_REF:0000002 | MODIFY | Summary: Cation transport is more precisely described as antiporter activity. Reason: The full-length protein was assayed as an antiporter. Use the existing antiporter term; a specific potassium:proton term is not asserted without confirming ion-specific assays. Proposed replacements: antiporter activity Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:0015297 antiporter activity | IEA GO_REF:0000002 | ACCEPT | Summary: Full-length CpaA has reconstituted antiporter activity. Reason: The proteoliposome assay independently supports antiport, beyond the sequence-based CPA2 family assignment. Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:0015459 potassium channel regulator activity | IEA GO_REF:0000104 | MODIFY | Summary: CpaA regulates its own antiporter through an RCK domain rather than serving as a potassium-channel gating subunit. Reason: The shared RCK-domain rule does not distinguish a separate gating subunit from a fused exchanger. KtrA regulates separate KtrB/KtrD conducting proteins, whereas CpaA itself contains the membrane antiporter module and has measured antiport activity. Neither the shared RCK domain nor the accessible CpaA assay establishes regulation of a potassium channel. Replace with antiporter activity and directly demonstrated cyclic-di-AMP binding. Proposed replacements: antiporter activity cyclic-di-AMP binding Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. PMID:23671116 a predicted cation/proton antiporter, CpaA, which as we show here also directly binds c-di-AMP. |
| GO:0016020 membrane | IEA GO_REF:0000120 | MODIFY | Summary: The cation/proton antiporter acts at the bacterial plasma membrane. Reason: Membrane insertion of full-length CpaA and its ion-exchange role support the bacterial plasma membrane, without assuming that an isolated RCK domain is itself membrane-spanning. Proposed replacements: plasma membrane Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:0043266 regulation of potassium ion transport | IEA GO_REF:0000104 | UNDECIDED | Summary: A potassium-specific regulatory process is not yet established from the inspected primary assay description. Reason: c-di-AMP changes CpaA antiporter activity, but the accessible primary abstract does not identify the transported ion or sign of regulation. This leaves the potassium-specific process unresolved, not disproven. Supporting Evidence: PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:0055085 transmembrane transport | IEA GO_REF:0000002 | MODIFY | Summary: The transport process includes proton movement through a cation/proton exchanger. Reason: Refine the generic transmembrane transport assertion to the existing proton transmembrane transport term; cation selectivity remains explicit uncertainty. Proposed replacements: proton transmembrane transport Supporting Evidence: PMID:23671116 a predicted cation/proton antiporter, CpaA, which as we show here also directly binds c-di-AMP. PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
| GO:1902600 proton transmembrane transport | IEA GO_REF:0000002 | ACCEPT | Summary: Proton transport is intrinsic to the cation/proton antiporter role. Reason: The cation/proton classification and independent full-length antiporter assay agree on proton-coupled exchange; neither requires a claim about which alkali cation is preferred. Supporting Evidence: PMID:23671116 a predicted cation/proton antiporter, CpaA, which as we show here also directly binds c-di-AMP. PMID:26171638 proteoliposome activity assay using the full-length SaCpaA membrane protein indicated that c-di-AMP binding alters its antiporter activity by approximately 40%. |
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