Bacterial D-ribose uptake and entry

A reusable bacterial route in which an RbsABC complex imports D-ribose, RbsD accelerates interconversion of the beta-pyranose and beta-furanose forms, and RbsK phosphorylates ribose to D-ribose 5-phosphate for entry into central carbon and nucleotide metabolism. Transcriptional regulation and downstream pentose-phosphate reactions are outside the module boundary.

The module is species-neutral. The experimentally characterized Escherichia coli K-12 rbs operon (RbsABC2 reconstitution, RbsB structure, RbsD NMR assay, RbsK kinetics) supplies the primary exemplar of every step, and the contiguous Pseudomonas putida KT2440 PP_2454-PP_2459 locus is a second, sequence-inferred implementation. RbsR regulates both loci but is not a transport or metabolic step. A second KT2440 pair, RbsA/PP_2759 and the permease PP_2760, lacks a neighboring substrate-binding protein and is not assigned to this module without substrate-specific evidence. The RbsB, RbsA and RbsC active units are grounded at PANTHER family level (PTHR46847, PTHR43790, PTHR32196) because the families are substrate-diversified carbohydrate-importer families: their names refer to D-allose or other systems, PTHR46847:SF1 and PTHR43790:SF3 also contain the allose-system proteins AlsB and AlsA, and the ribose permeases are split between PTHR32196:SF21 (E. coli RbsC) and SF72 (KT2440 RbsC). Ribose specificity is therefore carried by the exemplars and the operon, not by the family term; see the family reviews. RbsD is grounded at PTHR37831:SF1, whose members are D-ribose pyranases. RbsK carries no PANTHER family term: both RbsK exemplars are in PTHR10584:SF166, but the PTHR10584 family review finds SF166 functionally mixed and leaves ribokinase activity unresolved at subfamily level, so the role is anchored to the PAINT ribokinase node PTN000061929 and to the E. coli and KT2440 exemplars. The L-arabinose transporter IBA on E. coli RbsA from PTN001953353 is judged an over-propagation in the RbsA gene and PTHR43790 family reviews.