Primary Phaseolus vulgaris study (Sainz et al. 2015, Plant J). States that leghemoglobin is an abundant hemeprotein of legume nodules whose essential role is as an O2 transporter, and demonstrates in vivo nitration of PvLba at Tyr30 in the distal heme pocket by a nitrite/peroxide-dependent (oxoferryl-Lb) mechanism.

InterPro globin/leghemoglobin signatures (IPR000971, IPR001032, IPR012292, IPR019824) assign oxygen binding (GO:0019825) and heme binding (GO:0020037) to PvLba; both are core molecular functions of a plant globin.

A nucleus localization was transferred to PvLba by sequence similarity (ISS) from soybean leghemoglobin a (UniProtKB:P02240); it is not gene-specific experimental evidence and is not the functional site of the O2 carrier.

Subcellular-location keyword mapping assigns cytosol (SL-0091) and nucleus (SL-0191); the cytosol assignment matches the functional location of leghemoglobin in infected nodule cells.

SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.

For PvLba, the keyword "Oxygen transport" mapped to BOTH a correct core molecular function (oxygen carrier activity, GO:0005344) and a correct process (oxygen transport, GO:0015671); removing these was collateral damage. The keywords "Metal-binding"/"Iron" mapped to a broad term (metal ion binding) better replaced by heme/iron binding, and "Nodulation" mapped to an over-broad contextual process term.

FUNCTION - reversibly binds O2 through a pentacoordinated heme iron and, in root nodules, facilitates diffusion of oxygen to the bacteroids while preventing the bacterial nitrogenase from being inactivated by buffering dioxygen; essential for symbiotic nitrogen fixation.

Subcellular location is cytoplasm/cytosol (and nucleus by similarity); tissue specificity is root nodules; the protein is nitrated mainly at Tyr-31 (also Tyr-26, Tyr-134) and phosphorylated at Ser-46; belongs to the plant globin family.

PvLba is a nodule-localized plant globin whose primary role is to buffer and transport O2 in infected nodule cells, enabling high respiratory flux to bacteroids while keeping free O2 extremely low to protect the O2-labile nitrogenase ("oxygen paradox"); free O2 in infected cells is held sub-micromolar (<50 nM) and Lb occurs at millimolar concentration in the host-cell cytosol.

Best-supported annotation - molecular function = oxygen-binding/oxygen-carrier heme globin; process = oxygen transport / symbiotic nitrogen fixation support via nodule O2 homeostasis; location = infected host-cell cytosol of root nodules in proximity to symbiosomes.

Bean-specific PTM evidence - PvLba is nitrated in vivo at distal-pocket tyrosines (mainly Tyr30 in the study numbering; UniProt Tyr-31) by a nitrite/peroxide (ferryl-Lb) mechanism; the broader nodule hemoglobin network contributes to NO/ROS homeostasis.