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Weak and saturable protein-surfactant interactions in the denaturation of apo-α-lactalbumin by acidic and lactonic sophorolipid

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Abstract
Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited. Here, we present a study of the interactions between the model protein apo-alpha-lactalbumin (apo-aLA) and the biosurfactant sophorolipid (SL) produced by the yeast Starmerella bombicola. SL occurs both as an acidic and a lactonic form; the lactonic form (lactSL) is sparingly soluble and has a lower critical micelle concentration (cmc) than the acidic form [non-acetylated acidic sophorolipid (acidSL)]. We show that acidSL affects apo-aLA in a similar way to the related glycolipid biosurfactant rhamnolipid (RL), with the important difference that RL is also active below the cmc in contrast to acidSL. Using isothermal titration calorimetry data, we show that acidSL has weak and saturable interactions with apo-aLA at low concentrations; due to the relatively low cmc of acidSL (which means that the monomer concentration is limited to ca. 0-1 mM SL), it is only possible to observe interactions with monomeric acidSL at high apo-aLA concentrations. However, the denaturation kinetics of apo-aLA in the presence of acidSL are consistent with a collaboration between monomeric and micellar surfactant species, similar to RL and non-ionic or zwitterionic surfactants. Inclusion of diacetylated lactonic sophorolipid (lactSL) as mixed micelles with acidSL lowers the cmc and this effectively reduces the rate of unfolding, emphasizing that SL like other biosurfactants is a gentle anionic surfactant. Our data highlight the potential of these biosurfactants for future use in the detergent and pharmaceutical industry.
Keywords
sophorolipid, acidic form, lactonic form, protein denaturation, unfolding kinetics, binding stoichiometry, CANDIDA-BOMBICOLA, STARMERELLA-BOMBICOLA, BIOSURFACTANT, FERMENTATION

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Chicago
Andersen, Kell K, Brian S Vad, Sophie Roelants, Inge Van Bogaert, and Daniel E Otzen. 2016. “Weak and Saturable Protein-surfactant Interactions in the Denaturation of Apo-α-lactalbumin by Acidic and Lactonic Sophorolipid.” Frontiers in Microbiology 7.
APA
Andersen, K. K., Vad, B. S., Roelants, S., Van Bogaert, I., & Otzen, D. E. (2016). Weak and saturable protein-surfactant interactions in the denaturation of apo-α-lactalbumin by acidic and lactonic sophorolipid. FRONTIERS IN MICROBIOLOGY, 7.
Vancouver
1.
Andersen KK, Vad BS, Roelants S, Van Bogaert I, Otzen DE. Weak and saturable protein-surfactant interactions in the denaturation of apo-α-lactalbumin by acidic and lactonic sophorolipid. FRONTIERS IN MICROBIOLOGY. 2016;7.
MLA
Andersen, Kell K, Brian S Vad, Sophie Roelants, et al. “Weak and Saturable Protein-surfactant Interactions in the Denaturation of Apo-α-lactalbumin by Acidic and Lactonic Sophorolipid.” FRONTIERS IN MICROBIOLOGY 7 (2016): n. pag. Print.
@article{8510824,
  abstract     = {Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited. Here, we present a study of the interactions between the model protein apo-alpha-lactalbumin (apo-aLA) and the biosurfactant sophorolipid (SL) produced by the yeast Starmerella bombicola. SL occurs both as an acidic and a lactonic form; the lactonic form (lactSL) is sparingly soluble and has a lower critical micelle concentration (cmc) than the acidic form [non-acetylated acidic sophorolipid (acidSL)]. We show that acidSL affects apo-aLA in a similar way to the related glycolipid biosurfactant rhamnolipid (RL), with the important difference that RL is also active below the cmc in contrast to acidSL. Using isothermal titration calorimetry data, we show that acidSL has weak and saturable interactions with apo-aLA at low concentrations; due to the relatively low cmc of acidSL (which means that the monomer concentration is limited to ca. 0-1 mM SL), it is only possible to observe interactions with monomeric acidSL at high apo-aLA concentrations. However, the denaturation kinetics of apo-aLA in the presence of acidSL are consistent with a collaboration between monomeric and micellar surfactant species, similar to RL and non-ionic or zwitterionic surfactants. Inclusion of diacetylated lactonic sophorolipid (lactSL) as mixed micelles with acidSL lowers the cmc and this effectively reduces the rate of unfolding, emphasizing that SL like other biosurfactants is a gentle anionic surfactant. Our data highlight the potential of these biosurfactants for future use in the detergent and pharmaceutical industry.},
  articleno    = {1711},
  author       = {Andersen, Kell K and Vad, Brian S and Roelants, Sophie and Van Bogaert, Inge and Otzen, Daniel E},
  issn         = {1664-302X},
  journal      = {FRONTIERS IN MICROBIOLOGY},
  keyword      = {sophorolipid,acidic form,lactonic form,protein denaturation,unfolding kinetics,binding stoichiometry,CANDIDA-BOMBICOLA,STARMERELLA-BOMBICOLA,BIOSURFACTANT,FERMENTATION},
  language     = {eng},
  pages        = {9},
  title        = {Weak and saturable protein-surfactant interactions in the denaturation of apo-\ensuremath{\alpha}-lactalbumin by acidic and lactonic sophorolipid},
  url          = {http://dx.doi.org/10.3389/fmicb.2016.01711},
  volume       = {7},
  year         = {2016},
}

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