| Claim (function/localization/interaction/phenotype) | Evidence summary | Organism context (P. putida vs P. aeruginosa) | Key citation (with year, journal) | URL/DOI |
|---|---|---|---|---|
| OM lipoprotein with TPR/Sel1-like repeats | AlgK is experimentally shown to be lipidated in vivo, localized to outer-membrane fractions, and to carry an N-terminal lipoprotein signal/lipobox; crystal structure shows a TPR-rich superhelical scaffold (~9.5 TPR-like repeats), supporting a periplasmic protein–protein interaction role (pqac-00000020, pqac-00000026, pqac-00000015) | Direct evidence: *P. aeruginosa*; inference to *P. putida* KT2440/Q88NC7 supported by conserved AlgK-family/domain annotation | Keiski et al., 2010, *Structure*; Keiski, 2010, thesis/structural study | https://doi.org/10.1016/j.str.2009.11.015 ; https://doi.org/10.1016/j.str.2009.11.015 |
| Interacts with AlgE | Co-immunoprecipitation with AlgE-FLAG recovered AlgK, and loss of algK causes AlgE mislocalization to both inner- and outer-membrane fractions, indicating AlgK helps position/stabilize the AlgE export porin within the secretion apparatus (pqac-00000021, pqac-00000026) | Direct evidence: *P. aeruginosa* | Rehman et al., 2013, *Applied and Environmental Microbiology*; Keiski et al., 2010, *Structure* | https://doi.org/10.1128/AEM.00460-13 ; https://doi.org/10.1016/j.str.2009.11.015 |
| Interacts with AlgX | Pulldown of AlgK-His copurified AlgX in vivo/in cell-envelope preparations; later crystallography solved a direct AlgK–AlgX complex at 2.5 Å and mapped the interface to the N-terminus of AlgX and TPRs 9–10 of AlgK (pqac-00000021, pqac-00000010) | Interaction detected in *P. aeruginosa*; direct 2.5 Å complex structure reported for *P. putida* proteins | Rehman et al., 2013, *Applied and Environmental Microbiology*; Gheorghita et al., 2022, *Nature Communications* | https://doi.org/10.1128/AEM.00460-13 ; https://doi.org/10.1038/s41467-022-35131-6 |
| Required for high-molecular-weight alginate secretion | algK deletion abolishes or severely impairs alginate production/secretion; classical phenotypes include non-mucoidy and failure to recover high-molecular-weight polymer, consistent with AlgK being a required scaffold in synthase-dependent export (pqac-00000004, pqac-00000023) | Direct evidence: *P. aeruginosa*; applied by homology to *P. putida* AlgK family member Q88NC7 with caution | Rehman et al., 2013, *Applied and Environmental Microbiology*; Keiski et al., 2010, *Structure* | https://doi.org/10.1128/AEM.00460-13 ; https://doi.org/10.1016/j.str.2009.11.015 |
| Deletion leads to AlgL degradation products / short uronic acids | In algK mutants, nascent alginate is exposed to periplasmic alginate lyase AlgL, producing low-molecular-weight uronic acids instead of protected/exported polymer; this is a key functional signature of failed trans-envelope complex assembly (pqac-00000006, pqac-00000014, pqac-00000012) | Direct evidence: *P. aeruginosa*; mechanistic inference for *P. putida* homolog | Keiski et al., 2010, structural/functional study; Gheorghita et al., 2023, *FEMS Microbiology Reviews*; Serrato, 2024, *Biochemistry* chapter | https://doi.org/10.1016/j.str.2009.11.015 ; https://doi.org/10.1093/femsre/fuad060 ; https://doi.org/10.5772/intechopen.109295 |
| Proposed scaffold linking IM polymerase to OM export | Current model places AlgK as an OM-anchored periplasmic scaffold that helps connect Alg8/Alg44 polymerization at the inner membrane with AlgX-mediated periplasmic processing and AlgE-mediated outer-membrane export; mutual stability data also link AlgK with Alg44/AlgX (pqac-00000009, pqac-00000012) | Mostly direct in *P. aeruginosa*; family-wide model relevant to *P. putida* AlgK | Rehman dissertation excerpt; Serrato, 2024, *Biochemistry* chapter | https://doi.org/10.5772/intechopen.109295 |
| AlgK–AlgX complex binds alginate oligomers and supports export model | The 2.5 Å AlgK–AlgX structure and glycan-binding experiments showed AlgK/AlgKX bind alginate oligomers (polyM/polyMG), supporting a chaperone/conduit role for polymer transfer toward AlgE; disruption of the AlgK–AlgX interaction abolishes alginate production and biofilm attachment (pqac-00000010) | Direct structural evidence: *P. putida* proteins used for complex structure; functional interpretation in *P. aeruginosa* system | Gheorghita et al., 2022, *Nature Communications* | https://doi.org/10.1038/s41467-022-35131-6 |
| Proposed AlgEKX outer-membrane modification/secretion complex | Integrative structural modeling places AlgK on AlgE to create an electropositive conduit from the AlgX active site to the AlgE pore, rationalizing how modification and export are physically coupled across the periplasm/outer membrane (pqac-00000010, pqac-00000016) | Model integrates direct structural work on *P. putida* AlgKX with *P. aeruginosa* pathway biology | Gheorghita et al., 2022, *Nature Communications* | https://doi.org/10.1038/s41467-022-35131-6 |


*Table: This table summarizes the strongest functional-annotation evidence for AlgK (UniProt Q88NC7), separating direct findings from Pseudomonas aeruginosa and P. putida structural evidence. It highlights localization, interaction partners, mutant phenotypes, and the current structural model for alginate export.*