Specificity of a β-porphyranase produced by the carrageenophyte red alga Chondrus crispus and implications of this unexpected activity on red algal biology - Archive ouverte HAL Access content directly
Journal Articles Journal of Biological Chemistry Year : 2022

Specificity of a β-porphyranase produced by the carrageenophyte red alga Chondrus crispus and implications of this unexpected activity on red algal biology

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Abstract

The carrageenophyte red alga Chondrus crispus produces three family 16 glycoside hydrolases (CcGH16-1, -2 and -3). Phylogenetically, the red algal GH16 members are closely related to bacterial GH16 homologues from subfamilies 13 and 14, which have characterized marine bacterial β-carrageenase and β-porphyranase activities, respectively, yet the functions of these CcGH16 hydrolases have not been determined. Here, we first confirmed the gene locus of the ccgh16-3 gene in the alga to facilitate further investigation. Next, our biochemical characterization of CcGH16-3 revealed an unexpected β-porphyranase activity, since porphyran is not a known component of the C. crispus extracellular matrix. Kinetic characterization was undertaken on natural porphyran substrate with an experimentally determined molecular weight. We found CcGH16-3 has a pH optimum between 7.5-8.0; however, it exhibits reasonably stable activity over a large pH range (pH 7.0-9.0). CcGH16-3 has a KM of 4.0 ± 0.8 μM, a kcat of 79.9 ± 6.9 s-1 and a kcat/KM of 20.1 ± 1.7 μM-1.s-1. We structurally examined fine enzymatic specificity by performing a subsite dissection. CcGH16-3 has a strict requirement for D-galactose and L-galactose-6-sulfate in its -1 and +1 subsites, respectively, whereas the outer subsites are less restrictive. CcGH16-3 is one of a handful of algal enzymes characterized with a specificity for a polysaccharide unknown to be found in their own extracellular matrix. This β-porphyranase activity in a carrageenophyte red alga may provide defense against red algal pathogens or, alternatively, provide a competitive advantage in niche colonization.

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hal-03894158 , version 1 (12-12-2022)

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G. Manat, M. Fanuel, D. Jouanneau, M. Jam, J. Mac-Bear, et al.. Specificity of a β-porphyranase produced by the carrageenophyte red alga Chondrus crispus and implications of this unexpected activity on red algal biology. Journal of Biological Chemistry, 2022, pp.102707. ⟨10.1016/j.jbc.2022.102707⟩. ⟨hal-03894158⟩
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