Momsen M M, Dahim M, Brockman H L
The Hormel Institute, University of Minnesota, Austin, Minnesota 55912, USA.
Biochemistry. 1997 Aug 19;36(33):10073-81. doi: 10.1021/bi9703857.
The interaction of the pancreatic lipase cofactor colipase with a diacylphosphatidylcholine, acylglycerols, and free fatty acid was investigated by monitoring its adsorption to monomolecular lipid films. Surface pressure and colipase surface concentration were measured as a function of the initial lipid concentration and composition. Colipase adsorbs to a level of 28-30 pmol/cm2 to form a close-packed monolayer of protein and interacts strongly with all lipids when the lipid chain:colipase ratio is </=3. Consideration of the size difference between the protein and acyl groups suggests that in this regime the lipid is occupying the voids between tightly packed protein molecules. At lipid chain:colipase ratios >3, the triacylglycerol is excluded from the monolayer phase. Phosphatidylcholine, diacylglycerols, and free fatty acid remain in the monolayer phase up to </=25 lipid chain:colipase ratios. Geometrically over this range of compositions, the colipase molecules should be separated by up to 0-2 acyl chains. At higher lipid chain:colipase ratios, diacylglycerols are likely excluded from the monolayer phase. Anomalous behavior is observed with the fatty acid which at lipid chain:colipase ratios >25 induces higher levels of colipase adsorption than at lower ratios. This suggests the formation of a novel structure involving fatty acid and/or colipase. Phosphatidylcholine also remains in the interface at lipid chain:colipase ratios >3 but shows little additional interaction with colipase. However, fluorescence microscopy suggests that the phosphatidylcholine and colipase are miscible in the interface. The specificity demonstrated in this study suggests that colipase may regulate the type of surfaces to which colipase and, hence, lipase bind and may control the species distribution of substrate to which bound lipase is exposed.
通过监测胰脂肪酶辅因子共脂肪酶对单分子脂质膜的吸附作用，研究了其与二酰基磷脂酰胆碱、酰基甘油和游离脂肪酸之间的相互作用。测量了表面压力和共脂肪酶表面浓度随初始脂质浓度和组成的变化。当脂质链与共脂肪酶的比例≤3时，共脂肪酶吸附至28 - 30 pmol/cm²的水平，形成紧密堆积的蛋白质单层，并与所有脂质强烈相互作用。考虑到蛋白质和酰基之间的大小差异，表明在这种情况下脂质占据了紧密堆积的蛋白质分子之间的空隙。当脂质链与共脂肪酶的比例>3时，三酰基甘油被排除在单层相之外。在脂质链与共脂肪酶的比例≤25时，磷脂酰胆碱、二酰基甘油和游离脂肪酸仍保留在单层相中。在此组成范围内，从几何学角度来看，共脂肪酶分子之间应被多达0 - 2个酰基链隔开。在更高的脂质链与共脂肪酶比例下，二酰基甘油可能被排除在单层相之外。观察到脂肪酸存在异常行为，当脂质链与共脂肪酶的比例>25时，其诱导的共脂肪酶吸附水平高于较低比例时。这表明形成了一种涉及脂肪酸和/或共脂肪酶的新结构。在脂质链与共脂肪酶的比例>3时，磷脂酰胆碱也保留在界面中，但与共脂肪酶几乎没有额外的相互作用。然而，荧光显微镜显示磷脂酰胆碱和共脂肪酶在界面中是可混溶的。本研究中所展示的特异性表明，共脂肪酶可能调节共脂肪酶以及因此脂肪酶所结合的表面类型，并可能控制结合的脂肪酶所接触的底物的种类分布。
