mexB encodes the inner-membrane transporter subunit of an RND (resistance-nodulation-cell division) family multidrug efflux pump. It is a large multi-pass integral membrane protein of the cytoplasmic (inner) membrane that uses the transmembrane proton-motive force as an antiporter to capture substrates from the periplasm and outer leaflet of the inner membrane and pump them outward. Acting together with a periplasmic membrane-fusion (adaptor) protein and an outer-membrane channel, it forms a tripartite efflux system that expels a broad range of structurally diverse antibiotics, solvents, dyes and other xenobiotics across the cell envelope, contributing to intrinsic multidrug and solvent resistance in P. putida.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Correct cellular component. The RND transporter subunit is a multi-pass integral protein of the bacterial plasma (inner) membrane (UniProt SUBCELLULAR LOCATION; multi-pass membrane protein). Accept as the informative localization. |
| GO:0015562 efflux transmembrane transporter activity | IEA GO_REF:0000002 | ACCEPT | Summary: Core molecular function. MexB-type RND proteins are the energized efflux transporter subunit that exports substrates outward across the membrane. Matches the UniProt "Efflux pump membrane transporter" name and RND family assignment. Accept. |
| GO:0016020 membrane | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct but general. "Membrane" is a broad parent of the plasma membrane localization already annotated. Keep as non-core in favor of the more specific GO:0005886. |
| GO:0022857 transmembrane transporter activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct but general parent of the efflux transporter activity. Keep as non-core in favor of the more specific efflux/xenobiotic transporter terms. |
| GO:0042908 xenobiotic transport | IEA GO_REF:0000002 | ACCEPT | Summary: Core biological process. The pump exports structurally diverse xenobiotics (antibiotics, solvents, dyes) out of the cell. Accept as a defining biological role. |
| GO:0042910 xenobiotic transmembrane transporter activity | IEA GO_REF:0000118 | ACCEPT | Summary: Core molecular function describing the substrate range. The transporter moves xenobiotics across the membrane; together with the efflux directionality term (GO:0015562) this captures the activity. Accept. |
| GO:0055085 transmembrane transport | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct but general parent process of xenobiotic transport. Keep as non-core in favor of the more specific GO:0042908. |
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