Protein--surfactant interactions between bovine lactoferrin and sophorolipids under neutral and acidic conditions

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From: Biochemistry and Cell Biology(Vol. 95, Issue 1)
Publisher: NRC Research Press
Document Type: Report
Length: 3,685 words
Lexile Measure: 1450L

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Abstract: To understand the protein-surfactant interactions between naturally derived sophorolipids (SLs) and bovine lactoferrin (bLf), we carried out spectroscopic, microscopic, and biochemical experiments under weakly acidic and neutral pH conditions. Particle size analysis, microscopy, and enzymatic digestion indicated that bLf and SLs interact with each other to form sheet-like and small aggregated structures reflecting the original self-organization of SLs at pH 5.0 and 7.0, respectively. Circular dichroism (CD) showed that SLs did not significantly affect the secondary structure of bLf.

Key words: lactoferrin, sophorolipids, protein-surfactant interaction, complex, electrostatic interaction.

Resume: Les auteurs ont realise des experiences en spectroscopie, en microscopie et biochimiques a pH faiblement acide ou neutre, afin de comprendre les interactions proteine-surfactant entre des sophorolipides derives naturellement (SL) et la lactoferrine bovine (bLf). L'analyse de la taille des particules, la microscopie et la digestion enzymatique indiquaient que la bLf et les SL interagissent l'une avec les autres pour former des structures en feuillets et en petits agregats, refletant respectivement l'auto-organisation originale des SL a pH 5,0 et 7,0. Le dichroisme circulaire (DC) a montre que les SL n'affectaient pas significativement la structure secondaire de la bLf. [Traduit par la Redaction]

Mots-cles: lactoferrine, sophorolipides, interaction proteine-surfactant, complexe, interaction electrostatique.

Introduction

Lactoferrin, first discovered in bovine milk, is a red-colored glycoprotein that can bind iron ions with high affinity (Sorensen and Sorensen 1940; Groves 1960). Bovine lactoferrin (bLf) is a single-chain protein consisting of 689 amino acid residues, with a molecular weight of 78 000 Da and an isoelectric point of pH 8.8 (Shimazaki et al. 1993; Moore et al. 1997). Since lactoferrin is associated with a diverse range of biochemical functions, it is widely accepted that it is a multifunctional protein that can be used in the manufacture of different products including foods, drugs, and cosmetics. Some of its important biological functions include anti-inflammatory activity, bacteriostatic activity, growth factor action, and bone formation (Lonnerdal and Suzuki 2013).

Among the various functions of lactoferrin, researchers have particularly focused on its role in stimulating skin keratinocyte function and wound re-epithelialization, originally reported by Tang et al. (2010). In our previous study, we demonstrated that bLf significantly increased tropoelastin expression in cultured fibroblasts, and this expression is efficiently promoted by addition of a novel skin penetration enhancer, acid-type sophorolipids (SLs) (Ishii et al. 2012). In the same study, we also observed that on addition of SLs, transdermal absorption of bLf through a model skin was enhanced up to 1.7-fold, possibly due to complex formation between bLf and SLs. However, the exact protein-surfactant interactions remain to be understood.

Acid-type SLs are produced from natural resources through fermentation by the nonpathogenic yeast Starmerella bombicola. These are surface-active glycolipids comprising a sophorose unit, which is a glucose disaccharide, glycosically linked to a hydroxyl fatty acid, as shown in Fig. 1 (Lang 2003; Ishii et al. 2012). According to a previous study, SL molecules tend to self-organize, forming giant twisted or helical ribbons in acidic conditions (pH < 5.5) (Zhou et al. 2004). The yield of...

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