title: The protein and lipid composition of the membrane of milk fat globules depends on their size.
abstract: In bovine milk, fat globules (MFG) have a heterogeneous size distribution with diameters ranging from 0.1 to 15 µm. Although efforts have been made to explain differences in lipid composition, little is known about the protein composition of MFG membranes (MFGM) in different sizes of MFG. In this study, protein and lipid analyses were combined to study MFG formation and secretion. Two different sized MFG fractions (7.6±0.9 µm and 3.3±1.2 µm) were obtained by centrifugation. The protein composition of MFGM in the large and small MFG fractions was compared using mass-spectrometry-based proteomics techniques. The lipid composition and fatty acid composition of MFG was determined using HPLC-evaporative light-scattering detector and gas chromatography, respectively. Two frequently studied proteins in lipid droplet biogenesis, perilipin-2 and TIP47, were increased in the large and small MFG fractions, respectively. In the large MFG fraction, besides perilipin-2, cytoplasmic vesicle proteins (heat shock proteins, 14-3-3 proteins, and Rabs), microfilaments and intermediate filament-related proteins (actin and vimentin), host defense proteins (cathelicidins), and phosphatidylinositol were higher in concentration. On the other hand, cholesterol synthesis enzymes [lanosterol synthase and sterol-4-α-carboxylate 3-dehydrogenase (decarboxylating)], cholesterol, unsaturated fatty acids, and phosphatidylethanolamine were, besides TIP47, higher in concentration in the small MFG fraction. These results suggest that vesicle proteins, microfilaments and intermediate filaments, cholesterol, and specific phospholipids play an important role in lipid droplet growth, secretion, or both. The observations from this study clearly demonstrated the difference in protein and lipid composition between small and large MFG fractions. Studying the role of these components in more detail in future experiments may lead to a better understanding of fat globule formation and secretion.
authors.affiliation: Dairy Science and Technology, Food Quality and Design group, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, the Netherlands; Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, the Netherlands; Institute of Agro-Products Processing Science and Technology, Chinese Academy of Agricultural Sciences (CAAS), 100193, Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.affiliation: Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Nurit
authors.initials: N
authors.lastname: Argov-Argaman
authors.affiliation: Dairy Science and Technology, Food Quality and Design group, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, the Netherlands.
authors.forename: Jeni
authors.initials: J
authors.lastname: Anggrek
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, the Netherlands.
authors.forename: Sjef
authors.initials: S
authors.lastname: Boeren
authors.affiliation: Dairy Science and Technology, Food Quality and Design group, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, the Netherlands.
authors.forename: Toon
authors.initials: T
authors.lastname: van Hooijdonk
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, the Netherlands.
authors.forename: Jacques
authors.initials: J
authors.lastname: Vervoort
authors.affiliation: Dairy Science and Technology, Food Quality and Design group, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, the Netherlands. Electronic address: kasper.hettinga@wur.nl.
authors.forename: Kasper Arthur
authors.initials: KA
authors.lastname: Hettinga
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D002849:Chromatography, Gas / Q000662:veterinary; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D006017:Glycolipids / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry*; D066292:Lipid Droplets; D008055:Lipids / Q000737:chemistry*; D013058:Mass Spectrometry / Q000662:veterinary; D008566:Membranes / Q000737:chemistry; D008894:Milk Proteins / Q000737:chemistry*; D020543:Proteome
chemical_list: D006017:Glycolipids; D006023:Glycoproteins; D008055:Lipids; D008894:Milk Proteins; D020543:Proteome; C110367:milk fat globule
keywords: fat globule; membrane proteome; milk; phospholipids; triglycerides