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Effect of protease mutations on the production of xylanases in Streptomyces lividans

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Three protease mutants — 7 (tap), 12 (tap, ssp), and 17 (multiple mutations) — of Streptomyces lividans were tested for their influence on protein secretion. Streptomyces lividans grown in xylan secretes 3 xylanases (A, B, and C). Xylanases A (XlnA) and B (XlnB) are secreted by the Sec pathway, whereas xylanase C (XlnC) is secreted by the Tat pathway. The production of XlnA and XlnC was affected in the mutants, suggesting that the mutations interfered with both Sec- and Tat-secretion systems. However, the processing rate for the Sec and Tat precursor was similar to the wild-type strain, indicating that the mutations had no direct effect on secretion. Streptomyces lividans naturally produced 2forms of XlnB: XlnB1, which contains the catalytic and the xylan-binding domains, and XlnB2, which contains the catalytic domain only. There was no change from the wild-type strain in the ratio of XlnB1/XlnB2 produced by the mutants, indicating that these proteases are not involved in this process. Although XlnA1, partially truncated in its xylan-binding domain, was rapidly degraded to its catalytic domain (XlnA2) in the wild-type strain, the rate of conversion was reduced in the 3 mutants, indicating that the proteases participated to some extent in this proteolytic process.

L’influence des protéases sur la sécrétion de protéines a été testée chez trois souches mutantes de Streptomyces lividans: les mutants 7 (tap), 12 (tap, ssp) et 17 (mutations multiples). Streptomyces lividans cultivée sur du xylane sécrète 3 xylanases (A, B et C). Les xylanases A (XlnA) et B (XlnB) sont sécrétées via la voie Sec, alors que la xylanase C (XlnC) est décrétée via la voie Tat. La production de XlnA et XlnC était affectée chez les mutants, suggérant que ces mutations interfèrent avec les deux systèmes de sécrétion, Sec et Tat. Cependant, le taux de maturation des précurseurs de Sec et Tat était similaire à celui des souches sauvages, indiquant que les mutations n’avaient pas d’effets directs sur la sécrétion. S.lividans produit naturellement 2formes de XlnB, XlnB1 qui contient le domaine catalytique et le domaine de liaison du xylane, et XlnB2, qui ne contient que le domaine catalytique. Il n’y avait pas de changements dans le rapport XlnB1/XlnB2 des mutants comparativement à la souche sauvage, indiquant que ces protéases ne sont pas impliquées dans ce processus. Finalement, alors que XlnA1 dont le domaine de liaison au xylane est partiellement tronqué est rapidement dégradé en son domaine catalytique XlnA2 chez la souche sauvage, le taux de conversion était réduit chez les 3 mutants, indiquant que les protéases participaient d’une certaine façon à cette protéolyse.

Document Type: Research Article

Publication date: 2007-06-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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