Water-soluble proteins as well as membrane-bound proteins associate with membrane surfaces and bind specific lipid molecules in specific sites on the protein. Membrane surfaces include the traditional bilayer membranes of cells and subcellular organelles formed by phospholipids. Monolayer membranes include the outer monolayer phospholipid surface of intracellular lipid droplets of triglycerides and various lipoproteins including HDL, LDL, VLDL, and chylomicrons. These lipoproteins circulate in our blood and lymph systems and contain triglycerides, cholesterol, cholesterol esters, and proteins in their interior, and these are sometimes interspersed on their surfaces. Similar lipid–water interfaces also occur in mixed micelles of phospholipids and bile acids in our digestive system, which may also include internalized triglycerides and cholesterol esters. Diacyl phospholipids constitute the defining molecules of biological membranes. Phospholipase A₁ (PLA₁) hydrolyzes phospholipid acyl chains at the sn-1 position of membrane phospholipids, phospholipase A₂ (PLA₂) hydrolyzes acyl chains at the sn-2 position, phospholipase C (PLC) hydrolyzes the glycerol–phosphodiester bond, and phospholipase D (PLD) hydrolyzes the polar group–phosphodiester bond. Of the phospholipases, the PLA₂s have been the most well studied at the mechanistic level. The PLA₂ superfamily consists of 16 groups and numerous subgroups, and each is generally described as one of 6 types. The most well studied of the PLA₂s include extensive genetic and mutational studies, complete lipidomics specificity characterization, and crystallographic structures. This Account will focus principally on results from deuterium exchange mass spectrometric (DXMS) studies of PLA₂ interactions with membranes and extensive molecular dynamics (MD) simulations of their interactions with membranes and specific phospholipids bound in their catalytic and allosteric sites. These enzymes either are membrane-bound or are water-soluble and associate with membranes before extracting their phospholipid substrate molecule into their active site to carry out their enzymatic hydrolytic reaction. We present evidence that when a PLA₂ associates with a membrane, the membrane association can result in a conformational change in the enzyme whereby the membrane association with an allosteric site on the enzyme stabilizes the enzyme in an active conformation on the membrane. We sometimes refer to this transition from a “closed” conformation in aqueous solution to an “open” conformation when associated with a membrane. The enzyme can then extract a single phospholipid substrate into its active site, and catalysis occurs. We have also employed DXMS and MD simulations to characterize how PLA₂s interact with specific inhibitors that could lead to potential therapeutics. The PLA₂s constitute a paradigm for how membranes interact allosterically with proteins, causing conformational changes and activation of the proteins to enable them to extract and bind a specific phospholipid from a membrane for catalysis, which is probably generalizable to intracellular and extracellular transport and phospholipid exchange processes as well as other specific biological functions. We will focus on the four main types of PLA₂, namely, the secreted (sPLA₂), cytosolic (cPLA₂), calcium-independent (iPLA₂), and lipoprotein-associated PLA₂ (Lp-PLA₂) also known as platelet-activating factor acetyl hydrolase (PAF-AH). Studies on a well-studied specific example of each of the four major types of the PLA₂ superfamily demonstrate clearly that protein subsites can show precise specificity for one of the phospholipid hydrophobic acyl chains, often the one at the sn-2 position, including exquisite sensitivity to the number and position of double bonds.

中文翻译：

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膜关联变构调节磷脂酶 A2 酶及其特异性

水溶性蛋白质以及膜结合蛋白与膜表面结合，并在蛋白质的特定位点结合特定的脂质分子。膜表面包括传统的细胞双层膜和由磷脂形成的亚细胞细胞器。单层膜包括甘油三酯和各种脂蛋白（包括HDL、LDL、VLDL和乳糜微粒）的细胞内脂滴的外单层磷脂表面。这些脂蛋白在我们的血液和淋巴系统中循环，其内部含有甘油三酯、胆固醇、胆固醇酯和蛋白质，有时散布在其表面。类似的脂水界面也出现在我们消化系统中磷脂和胆汁酸的混合胶束中，其中还可能包括内化的甘油三酯和胆固醇酯。二酰基磷脂构成生物膜的定义分子。磷脂酶 A ₁ (PLA ₁ ) 水解膜磷脂sn -1 位的磷脂酰基链，磷脂酶 A ₂ (PLA _{2 ) 水解}sn -2 位的酰基链，磷脂酶 C (PLC) 水解甘油-磷酸二酯键，磷脂酶 D (PLD) 水解极性​​基团 - 磷酸二酯键。在磷脂酶中，PLA ₂在机制水平上得到了最充分的研究。PLA ₂超家族由 16 个类群和众多亚类组成，每个类群通常被描述为 6 种类型之一。_{PLA 2}的最深入研究包括广泛的遗传和突变研究、完整的脂质组学特异性表征和晶体结构。本报告将主要关注 PLA ₂与膜相互作用的氘交换质谱 (DXMS) 研究结果，以及它们与膜和结合在其催化和变构位点的特定磷脂相互作用的广泛分子动力学 (MD) 模拟。这些酶要么是膜结合的，要么是水溶性的，并在将其磷脂底物分子提取到其活性位点以进行酶促水解反应之前与膜结合。我们提供的证据表明，当 PLA ₂当膜与膜缔合时，膜缔合可导致酶的构象变化，由此膜与酶上的变构位点缔合使酶稳定在膜上的活性构象。我们有时会提到这种从水溶液中的“闭合”构象到与膜结合时的“开放”构象的转变。然后，酶可以将单个磷脂底物提取到其活性位点，并发生催化作用。我们还采用 DXMS 和 MD 模拟来表征 PLA ₂如何与可能导致潜在治疗的特定抑制剂相互作用。PLA ₂构成了膜如何与蛋白质变构相互作用的范例，引起蛋白质的构象变化和激活，使它们能够从膜中提取和结合特定的磷脂进行催化，这可能适用于细胞内和细胞外的转运和磷脂交换过程以及其他特定的生物功能。我们将重点关注 PLA ₂的四种主要类型，即分泌型 (sPLA ₂ )、胞质型 (cPLA ₂ )、钙非依赖性型 (iPLA ₂ ) 和脂蛋白相关型 PLA ₂ (Lp-PLA ₂ )，也称为血小板激活因子乙酰水解酶（PAF-AH）。_{对 PLA 2}超家族四种主要类型中每一种的经过充分研究的具体例子的研究清楚地表明，蛋白质亚位点可以对磷脂疏水酰基链之一（通常是sn -2 位置的链）显示出精确的特异性，包括精致的对双键的数量和位置的敏感性。