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Saenger T, Schulte MF, Vordenbäumen S, Hermann FC, Bertelsbeck J, Meier K, Bleck E, Schneider M, Jose J. Structural Analysis of Breast-Milk α S1-Casein: An α-Helical Conformation Is Required for TLR4-Stimulation. Int J Mol Sci 2024; 25:1743. [PMID: 38339021 PMCID: PMC10855866 DOI: 10.3390/ijms25031743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 01/19/2024] [Accepted: 01/21/2024] [Indexed: 02/12/2024] Open
Abstract
Breast-milk αS1-casein is a Toll-like receptor 4 (TLR4) agonist, whereas phosphorylated αS1-casein does not bind TLR4. The objective of this study was to analyse the structural requirements for these effects. In silico analysis of αS1-casein indicated high α-helical content with coiled-coil characteristics. This was confirmed by CD-spectroscopy, showing the α-helical conformation to be stable between pH 2 and 7.4. After in vitro phosphorylation, the α-helical content was significantly reduced, similar to what it was after incubation at 80 °C. This conformation showed no in vitro induction of IL-8 secretion via TLR4. A synthetic peptide corresponding to V77-E92 of αS1-casein induced an IL-8 secretion of 0.95 ng/mL via TLR4. Our results indicate that αS1-casein appears in two distinct conformations, an α-helical TLR4-agonistic and a less α-helical TLR4 non-agonistic conformation induced by phosphorylation. This is to indicate that the immunomodulatory role of αS1-casein, as described before, could be regulated by conformational changes induced by phosphorylation.
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Affiliation(s)
- Thorsten Saenger
- Institute for Pharmaceutical and Medicinal Chemistry, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany; (T.S.); (M.F.S.)
| | - Marten F. Schulte
- Institute for Pharmaceutical and Medicinal Chemistry, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany; (T.S.); (M.F.S.)
| | - Stefan Vordenbäumen
- Department of Rheumatology and Hiller Research Unit Rheumatology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Moorenstr. 5, 40225 Düsseldorf, Germany
| | - Fabian C. Hermann
- Institute for Pharmaceutical Biology and Phytochemie, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany
| | - Juliana Bertelsbeck
- Institute for Pharmaceutical and Medicinal Chemistry, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany; (T.S.); (M.F.S.)
| | - Kathrin Meier
- Institute for Pharmaceutical and Medicinal Chemistry, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany; (T.S.); (M.F.S.)
| | - Ellen Bleck
- Department of Rheumatology and Hiller Research Unit Rheumatology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Moorenstr. 5, 40225 Düsseldorf, Germany
| | - Matthias Schneider
- Department of Rheumatology and Hiller Research Unit Rheumatology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Moorenstr. 5, 40225 Düsseldorf, Germany
| | - Joachim Jose
- Institute for Pharmaceutical and Medicinal Chemistry, University of Münster, PharmaCampus, Correnstr. 48, 48149 Münster, Germany; (T.S.); (M.F.S.)
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