Romano R, Musiol H J, Weyher E, Dufresne M, Moroder L
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Biopolymers. 1992 Nov;32(11):1545-58. doi: 10.1002/bip.360321112.
The (2RS)-1,2-dipalmitoyl-3-mercaptoglycerol/-, (2RS)-1,2-dimyristoyl-3-mercaptoglycerol/-, and (2RS)-1-myristoyl-2-palmitoyl-3-mercaptoglycerol/maleoyl-bet a-alanyl- [Nle15]-human-gastrin-(2-17) adducts were prepared as lipo-gastrin derivatives of explicitly primary amphiphilic properties. As representative of this class of lipo-gastrins, the dimyristoyl derivative has been thoroughly characterized in its aggregational state since, among the three compounds, theoretically it should exhibit the lowest degree of lipid character. It aggregates in aqueous solution to form monodispersed unilamellar spherical vesicles with dislocation of the peptide moiety at the bilayer surface in predominantly unordered structure. The liposomes are remarkably stable toward solubilization with trifluoroethanol and toward vesicle to micelle transition with neutral and negatively charged surfactants even above their critical micellar concentrations. Asymmetric fusion with the detergent micelles induces polydispersion of the liposomes in terms of shape and size without affecting in significant manner the mode of display of the gastrin portions at the bilayer surface. Only the positively charged hexadecyltrimethylammonium hydroxide provokes the collapse of the vesicles into mixed micelles with concomitant altered dislocation of the gastrin-peptide in the new aggregational state. Despite the lipid properties of the gastrin derivatives, i.e., formation of liposomes, they retain remarkable receptor affinities (IC50 = 1.5 x 10(-9) M for myristoyl-palmitoyl-gastrin, IC50 = 2.0 x 10(-9) M for di-myristoyl-gastrin and IC50 = 3.1 x 10(-9) M for di-palmitoyl-gastrin vs IC50 = 2.8 x 10(-10) M for Nle15-gastrin). Since the displacement of radiolabeled Nle15-gastrin from rat pancreatic acinar cell line membrane preparations by both the parent gastrin hormone and the three lipo-gastrins occurs in parallel manner, the data support a mechanism of receptor occupancy via accumulation of the gastrins at the membrane surface and their two-dimensional diffusion to the target receptor. Thereby the differentiated decrease of affinity in function of fatty acid chain length has to be attributed to the energetically more or less favored transfer of the monomers from the donor vesicles to the acceptor membranes. Moreover, according to this model migration of the lipo-gastrins with their interdigitating di-fatty-acyl moieties should be delayed, again in lipid structure-dependent manner, in comparison to the parent gastrin molecule, which is free to float in the membrane interfacial phase.
制备了(2RS)-1,2-二棕榈酰基-3-巯基甘油/-、(2RS)-1,2-二肉豆蔻酰基-3-巯基甘油/-和(2RS)-1-肉豆蔻酰基-2-棕榈酰基-3-巯基甘油/马来酰-β-丙氨酰-[Nle15]-人胃泌素-(2 - 17)加合物，作为具有明确一级两亲性质的脂胃泌素衍生物。作为这类脂胃泌素的代表，二肉豆蔻酰基衍生物的聚集状态已得到充分表征，因为在这三种化合物中，理论上它应表现出最低程度的脂质特性。它在水溶液中聚集形成单分散的单层球形囊泡，肽部分在双层表面错位，主要呈无序结构。这些脂质体对三氟乙醇的溶解以及对中性和带负电荷表面活性剂诱导的囊泡向胶束转变具有显著稳定性，即使在表面活性剂临界胶束浓度以上也是如此。与去污剂胶束的不对称融合会导致脂质体在形状和大小方面出现多分散性，但不会显著影响胃泌素部分在双层表面的展示方式。只有带正电荷的十六烷基三甲基氢氧化铵会促使囊泡塌陷成混合胶束，同时胃泌素肽在新的聚集状态下的错位发生改变。尽管胃泌素衍生物具有脂质特性，即形成脂质体，但它们仍保留显著的受体亲和力（肉豆蔻酰基-棕榈酰基-胃泌素的IC50 = 1.5×10⁻⁹ M，二肉豆蔻酰基-胃泌素的IC50 = 2.0×10⁻⁹ M，二棕榈酰基-胃泌素的IC50 = 3.1×10⁻⁹ M，而Nle15-胃泌素的IC50 = 2.8×10⁻¹⁰ M）。由于母体胃泌素激素和三种脂胃泌素都以平行方式从大鼠胰腺腺泡细胞系膜制剂中置换放射性标记的Nle15-胃泌素，这些数据支持一种通过胃泌素在膜表面积累及其二维扩散到靶受体来占据受体的机制。因此，亲和力随脂肪酸链长度的差异降低必须归因于单体从供体囊泡到受体膜的能量上或多或少有利的转移。此外，根据该模型，与可在膜界面相中自由漂浮的母体胃泌素分子相比，具有相互交错的二脂肪酸酰基部分的脂胃泌素的迁移应以脂质结构依赖的方式再次延迟。
