Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Biochemistry. 2009 Mar 3;48(8):1691-701. doi: 10.1021/bi801710g.
Prenylation is a posttranslational modification whereby C-terminal lipidation leads to protein localization to membranes. A C-terminal "Ca(1)a(2)X" sequence has been proposed as the recognition motif for two prenylation enzymes, protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I. To define the parameters involved in recognition of the a(2) residue, we performed structure-activity analysis which indicates that FTase discriminates between peptide substrates based on both the hydrophobicity and steric volume of the side chain at the a(2) position. For nonpolar side chains, the dependence of the reactivity on side chain volume at this position forms a pyramidal pattern with a maximal activity near the steric volume of valine. This discrimination occurs at a step in the kinetic mechanism that is at or before the farnesylation step. Furthermore, a(2) selectivity is also affected by the identity of the adjacent X residue, leading to context-dependent substrate recognition. Context-dependent a(2) selectivity suggests that FTase recognizes the sequence downstream of the conserved cysteine as a set of two or three cooperative, interconnected recognition elements as opposed to three independent amino acids. These findings expand the pool of proposed FTase substrates in cells. A better understanding of the molecular recognition of substrates performed by FTase will aid in both designing new FTase inhibitors as therapeutic agents and characterizing proteins involved in prenylation-dependent cellular pathways.
prenylation 是一种翻译后修饰，通过这种修饰，C 末端脂质化导致蛋白质定位到膜上。一个 C 末端的“Ca(1)a(2)X”序列被提议为两种 prenylation 酶，即蛋白质法尼基转移酶（FTase）和蛋白质 geranylgeranyltransferase 型 I 的识别基序。为了定义识别 a(2)残基所涉及的参数，我们进行了结构-活性分析，该分析表明 FTase 基于 a(2)位置侧链的疏水性和立体体积来区分肽底物。对于非极性侧链，该位置侧链体积对反应性的依赖性形成一个金字塔模式，在缬氨酸的立体体积附近具有最大活性。这种区分发生在动力学机制中的一个步骤中，即在法尼基化步骤之前或之中。此外，a(2)选择性还受到相邻 X 残基的身份的影响，导致上下文相关的底物识别。上下文相关的 a(2)选择性表明，FTase 将保守半胱氨酸下游的序列识别为一组两个或三个协作的、相互连接的识别元件，而不是三个独立的氨基酸。这些发现扩大了细胞中拟议的 FTase 底物池。更好地理解 FTase 对底物的分子识别将有助于设计新的 FTase 抑制剂作为治疗剂，并表征参与 prenylation 依赖性细胞途径的蛋白质。
