Liu Shu, Kumar Kiran, Bell Tracey, Ramamoorthy Ayyalusamy, Van Winkle David, Lenhert Steven
Department of Biological Science and Integrative Nanoscience Institute, Florida State University, Tallahassee, FL 32306, USA.
Department of Physics, Florida State University, Tallahassee, FL 32306, USA.
Membranes (Basel). 2024 Jul 30;14(8):168. doi: 10.3390/membranes14080168.
Lipids have not traditionally been considered likely candidates for catalyzing reactions in biological systems. However, there is significant evidence that aggregates of amphiphilic compounds are capable of catalyzing reactions in synthetic organic chemistry. Here, we demonstrate the potential for the hydrophobic region of a lipid bilayer to provide an environment suitable for catalysis by means of a lipid aggregate capable of speeding up a chemical reaction. By bringing organic molecules into the nonpolar or hydrophobic region of a lipid bilayer, reactions can be catalyzed by individual or collections of small, nonpolar, or amphiphilic molecules. We demonstrate this concept by the ester hydrolysis of calcein-AM to produce a fluorescent product, which is a widely used assay for esterase activity in cells. The reaction was first carried out in a two-phase octanol-water system, with the organic phase containing the cationic amphiphiles cetyltrimethylammonium bromide (CTAB) or octadecylamine. The octanol phase was then replaced with phospholipid vesicles in water, where the reaction was also found to be carried out. The reaction was monitored using quantitative fluorescence, which revealed catalytic turnover numbers on a scale of 10-7 to 10-8 s for each system, which is much slower than enzymatic catalysis. The reaction product was characterized by H-NMR measurements, which were consistent with ester hydrolysis. The implications of thinking about lipids and lipid aggregates as catalytic entities are discussed in the context of biochemistry, pharmacology, and synthetic biology.
传统上，脂质并未被视为生物系统中催化反应的可能候选物。然而，有大量证据表明两亲性化合物的聚集体能够在合成有机化学中催化反应。在此，我们通过一种能够加速化学反应的脂质聚集体，证明了脂质双层的疏水区域具有提供适合催化环境的潜力。通过将有机分子带入脂质双层的非极性或疏水区域，反应可由单个或多个小的非极性或两亲性分子催化。我们通过钙黄绿素-AM的酯水解产生荧光产物来证明这一概念，这是一种在细胞中广泛用于检测酯酶活性的方法。该反应首先在两相辛醇-水系统中进行，有机相中含有阳离子两亲物十六烷基三甲基溴化铵（CTAB）或十八胺。然后将辛醇相替换为水中的磷脂囊泡，在其中也发现该反应能够进行。使用定量荧光监测反应，结果显示每个系统的催化周转数在10^-7至10^-8 s范围内，这比酶催化要慢得多。通过核磁共振氢谱（H-NMR）测量对反应产物进行了表征，结果与酯水解一致。本文在生物化学、药理学和合成生物学的背景下讨论了将脂质和脂质聚集体视为催化实体的意义。
