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Replacement of Pro 109 by His in TlpA, a thioredoxin‐like protein from Bradyrhizobium japonicum , alters its redox properties but not its in vivo functions
Author(s) -
Rossmann Reinhild,
Stern Dorothee,
Loferer Hannes,
Jacobi Alexander,
Glockshuber Rudi,
Hennecke Hauke
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)00270-6
Subject(s) - thioredoxin , dsba , periplasmic space , biochemistry , bradyrhizobium japonicum , dithiothreitol , glutaredoxin , ferredoxin thioredoxin reductase , chemistry , oxidoreductase , protein disulfide isomerase , wild type , biology , thioredoxin reductase , mutant , enzyme , gene , escherichia coli , rhizobiaceae , symbiosis , bacteria , genetics
TlpA, the membrane‐anchored, thioredoxin‐like protein from Bradyrhizobium japonicum , is essential for cytochrome aa 3 biogenesis. The periplasmic domain of TlpA was previously shown to have protein thiol:disulfide oxidoreductase activity and reducing properties similar to those of cytoplasmic thioredoxins. Here, we replaced the proline‐109 in its active‐site sequence C 107 V 108 P 109 C 110 by a histidine residue. The resulting active‐site motif (CVHC) resembles that of oxidizing thiol:disulfide oxidoreductases such as protein disulfide isomerase (PDI) and DsbA. Indeed, the TlpA variant P109H was by 66 mV more oxidizing than the wild‐type protein. Nevertheless, the altered protein was even more efficient in catalyzing the reduction of insulin disulfides by dithiothreitol than the wild‐type due to a faster recycling of its catalytically active, reduced form. Cells of B. japonicum expressing only the mutated tlpA gene had the same phenotypes as wild‐type cells, suggesting that the change in the redox potential of TlpA was not critical for its in vivo function.