| Category | Evidence-based details | Key source (author, year, DOI URL) |
|---|---|---|
| Gene/protein identity | CSN1S1 is identified as the gene encoding αS1-casein within the mammalian casein gene cluster (CSN1S1, CSN2, CSN1S2, CSN3) on chromosome 6; in human milk, αS1-casein is present at low abundance relative to other caseins. (pqac-00000001, pqac-00000004) | Runthala et al., 2023, https://doi.org/10.3390/molecules28052023 |
| Expression/localization | Caseins are synthesized in the mammary gland, processed through the ER/Golgi with post-translational modification, and secreted into milk as colloidal micelles; caseins reside in the alveolar lumen after secretion. (pqac-00000001, pqac-00000003) | Runthala et al., 2023, https://doi.org/10.3390/molecules28052023 |
| Role in micelles | αS1-, αS2-, and β-caseins are calcium-binding phosphoproteins located mainly in the micelle interior, associating with colloidal calcium phosphate; κ-casein stabilizes the micelle surface. For humans, low αS-casein content suggests αS1 plays a comparatively minor but still canonical micellar role. (pqac-00000000, pqac-00000001) | Runthala et al., 2023, https://doi.org/10.3390/molecules28052023 |
| Quantitative abundance in human milk | Human milk total casein concentration is reported as 2.4–4.2 g/L. Relative casein composition is approximately αS1 3%, αS2 absent, β 70%, κ 27% (ratio 3:70:27). Mean human casein micelle diameter is 64–80 nm. (pqac-00000004) | Runthala et al., 2023, https://doi.org/10.3390/molecules28052023 |
| Bioactive peptide Casoxin D | Human Casoxin D is derived from αS1-casein fragment 158–164 with sequence YVPFPPF. Reviews classify casoxins as opioid antagonists; a 2020 synthesis reports receptor selectivity for MOP or DOP and notes digestion/proteolysis as a source of such peptides, with additional PBMC immunomodulatory assay effects described. (pqac-00000007, pqac-00000008, pqac-00000005) | EFSA review, 2009, https://doi.org/10.2903/j.efsa.2009.231r; Haq, 2020, https://doi.org/10.1007/978-981-15-6102-3 |
| Applications/implications | Casein composition and micelle organization influence dairy functionality (e.g., cheese/yogurt processing), stomach coagulation, digestibility, and allergenicity. Reviews also discuss exploiting casein structural differences to develop improved nutritional/industrial casein ingredients; casoxin D has been discussed as a therapeutic concept/patented opioid-antagonist peptide, but direct recent human CSN1S1 implementation evidence is limited. (pqac-00000000, pqac-00000001, pqac-00000005) | Runthala et al., 2023, https://doi.org/10.3390/molecules28052023; Haq, 2020, https://doi.org/10.1007/978-981-15-6102-3 |


*Table: This table compiles the core evidence-based functional annotation for human CSN1S1/alpha-S1-casein, including localization, micelle role, abundance, and the derived peptide casoxin D. It is useful as a concise reference for the main supported claims and their source provenance.*