Bacterial fused-relay fructose PTS uptake and catabolism

A bacterial fused-relay mechanism couples phosphoenolpyruvate-driven histidine phosphorylation to fructose translocation and formation of fructose 1-phosphate, followed by ATP-dependent formation of fructose 1,6-bisphosphate. A FruB polypeptide carries enzyme-I, HPr and fructose-specific EIIA regions; a separate FruA polypeptide combines EIIB phosphotransfer and EIIC translocation functions. Additional EIIB-like regions occur in several FruA exemplars. Nitrogen-regulatory PTS signaling and metabolism downstream of fructose 1,6-bisphosphate are outside the boundary.

The Bacteria context bounds this fused-relay implementation rather than asserting universal bacterial capacity. Demonstrated systems and sequence-qualified comparisons span alpha- and gammaproteobacteria. Deinococcus provides a separate strain boundary: the older assayed system uses ATP, whereas resequenced ATCC13939K has a restored full FruB ORF. This is not yet proof of native PEP-dependent uptake. E. coli FruA/FruK are component comparators; E. coli FPr lacks EI and requires separate PtsI, so these two members do not make a complete fused-relay system. Xanthomonas historical assays used ATCC13951, while current exemplar sequences are ATCC33913 with recorded differences. Rhodobacter sequences match the original sequenced locus, and the Sp7 panel matches the experimentally prioritized main locus; do not substitute its paralog locus. PANTHER memberships are necessary family context, not sufficient architecture, donor, substrate or pathway evidence. Required-domain and required-function descriptors capture the additional conditions; no family name is treated as proof of these conditions. Family-level identifiers are combined with activity and same-protein architecture requirements; the named subfamilies do not define the mechanism. The audit checker applies explicit evidence rules to the production Boolean circuit. The compiler exposes ontology identifiers but does not automatically enforce a free-text fusion descriptor; a family-only oracle is insufficient. Ontology representation: GO lacks a molecular-function term for phosphate transfer from a fructose-PTS EIIA histidine to the cognate EIIB phosphocysteine at the FruB-to-FruA handoff. The un-termed FruB internal-relay annoton and the part-2-to-part-3 connection preserve this step; the corresponding PSEPK FruB gene review proposes an EIIA-to-EIIB phosphotransferase activity term. The same proposed EIIA-to-EIIB activity is also recorded in RHOCA FruB and AZOBR FruB1; this is an ontology request rather than an unresolved biological mechanism.