Lefèvre T, Subirade M
Centre de recherches en Sciences et Technologie du Lait (STELA), Faculté des sciences de l'agriculture et de l'alimentation, Université Laval, Pavillon Paul Comtois, Quebec, G1K 7P4, Sainte-Foy, Canada.
Int J Biol Macromol. 2000 Oct 10;28(1):59-67. doi: 10.1016/s0141-8130(00)00149-5.
Fourier transform infrared (FTIR) spectroscopy has been used to study, at a molecular level, the interactions between beta-lactoglobulin (BLG), the most abundant globular protein in milk, and some lipids (sphingomyelin, SM; dimyristoylphosphatidylcholine, DMPC; dipalmytoylphosphatidylcholine, DPPC; dimyristoylphosphatidylserine-sodium salt, DMPS; dipalmitoylphosphatidylserine-sodium salt, DPPS) constituting the milk fat globule membrane (MFGM). The interactions were monitored with respect to alteration in the secondary structure of BLG, as registered by the amide I' band, and phospholipid conformation, as revealed by the acyl chain and carbonyl bands. The results show that neither the conformation nor the thermotropism of neutral bilayers containing DMPC or DPPC is affected by BLG. Reciprocally, the secondary structure and thermal behaviour of pure BLG remain the same in the presence of PC. These results suggest that no interaction occurs between PC and BLG, in agreement with previous studies. However, it is found that BLG interacts with neutral bilayers constituted by milk SM lipids, increasing gauche conformers and thus conformational disorder of the lipid acyl chains. This perturbing effect has been attributed to a partial penetration of BLG into the hydrophobic core of the bilayer, which allows hydrophobic interactions between BLG and SM. Moreover, the fact that SM possesses the same headgroup of PC implies that the head group does not prevent the occurrence of BLG-lipid interactions and other lipid regions can control the binding of BLG to lipids. Furthermore, BLG was found to interact electrostatically with charged bilayers containing PS, leading to a rigidification of the lipid hydrocarbon chains and a dehydration of the interfacial region. This last effect suggests that the protein limits the accessibility of water molecules to the interfacial region of the phospholipids by its presence at the membrane surface.
傅里叶变换红外光谱（FTIR）已被用于在分子水平上研究牛奶中最丰富的球状蛋白β-乳球蛋白（BLG）与构成乳脂肪球膜（MFGM）的一些脂质（鞘磷脂，SM；二肉豆蔻酰磷脂酰胆碱，DMPC；二棕榈酰磷脂酰胆碱，DPPC；二肉豆蔻酰磷脂酰丝氨酸钠盐，DMPS；二棕榈酰磷脂酰丝氨酸钠盐，DPPS）之间的相互作用。通过酰胺I'带记录的BLG二级结构变化以及酰基链和羰基带揭示的磷脂构象变化来监测相互作用。结果表明，含有DMPC或DPPC的中性双层的构象和热致性均不受BLG影响。相反，在存在磷脂酰胆碱（PC）的情况下，纯BLG的二级结构和热行为保持不变。这些结果表明PC和BLG之间不发生相互作用，这与先前的研究一致。然而，发现BLG与由牛奶SM脂质构成的中性双层相互作用，增加了gauche构象异构体，从而增加了脂质酰基链的构象无序性。这种干扰作用归因于BLG部分渗透到双层的疏水核心中，这使得BLG与SM之间能够发生疏水相互作用。此外，SM与PC具有相同的头部基团这一事实意味着头部基团不会阻止BLG-脂质相互作用的发生，并且其他脂质区域可以控制BLG与脂质的结合。此外，发现BLG与含有PS的带电双层发生静电相互作用，导致脂质烃链僵化和界面区域脱水。最后这一效应表明，蛋白质通过其在膜表面的存在限制了水分子进入磷脂界面区域的可及性。
