Caselli Anna, Taddei Maria Letizia, Bini Chiara, Paoli Paolo, Camici Guido, Manao Giampaolo, Cirri Paolo, Ramponi Giampietro
Department of Biochemical Sciences and Center for Research, Transfer, High Education DENOTHE, University of Florence, Florence, Italy.
Biochemistry. 2007 May 29;46(21):6383-92. doi: 10.1021/bi0620858. Epub 2007 May 1.
Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are small enzymes that are ubiquitous in many organisms. They are important in biological processes such as cell proliferation, adhesion, migration, and invasiveness. LMW-PTP is expressed in mammalian cells as two isoforms (IF1 and IF2) originating through alternative splicing. We have previously shown that IF2 targets lipid rafts called caveolae and interacts with caveolin-1, their major structural protein. Caveolae are cholesterol- and sphingolipid-rich membrane microdomains that have been implicated in a variety of cellular functions, including signal transduction events. Caveolin-1 contains a scaffolding region that contributes to the binding of the protein to the plasma membrane and mediates protein omo- and etero-oligomerization. Interaction of many signaling molecules with the scaffolding domain sequesters them into caveolae and inhibits or suppresses their activities. Caveolin-interacting proteins usually have a typical sequence motif, also present in all the LMW-PTPs, which is characterized by aromatic or large hydrophobic residues in specific positions. We have examined here the interaction of the LMW-PTP isoforms with caveolin-1 and its molecular mechanism, together with the consequences for their tyrosine phosphatase activities. We found that IF1 and IF2 are both capable of interacting with defined regions of caveolin-1 and that their putative caveolin binding sequence motif is not responsible for the association. The formation of LMW-PTP/caveolin-1 complexes is accompanied by modulation of the enzyme activities, and the inhibitory effect elicited against IF1 is stronger than that against IF2. The caveolin scaffolding domain is directly involved in the observed phenomena.
低分子量蛋白酪氨酸磷酸酶（LMW - PTPs）是在许多生物体中普遍存在的小酶。它们在细胞增殖、黏附、迁移和侵袭等生物过程中发挥重要作用。LMW - PTP在哺乳动物细胞中以两种通过可变剪接产生的异构体（IF1和IF2）形式表达。我们之前已经表明，IF2靶向称为小窝的脂筏，并与小窝蛋白 - 1（其主要结构蛋白）相互作用。小窝是富含胆固醇和鞘脂的膜微区，参与多种细胞功能，包括信号转导事件。小窝蛋白 - 1包含一个支架区域，该区域有助于蛋白质与质膜结合，并介导蛋白质的同聚和异聚。许多信号分子与支架结构域的相互作用将它们隔离到小窝中，并抑制或压制它们的活性。与小窝蛋白相互作用的蛋白质通常具有一个典型的序列基序，所有LMW - PTPs中也存在该基序，其特征是在特定位置具有芳香族或大的疏水残基。我们在此研究了LMW - PTP异构体与小窝蛋白 - 1的相互作用及其分子机制，以及对它们酪氨酸磷酸酶活性的影响。我们发现IF1和IF2都能够与小窝蛋白 - 1的特定区域相互作用，并且它们假定的小窝蛋白结合序列基序并非这种结合的原因。LMW - PTP/小窝蛋白 - 1复合物的形成伴随着酶活性的调节，并且对IF1产生的抑制作用比对IF2的更强。小窝蛋白支架结构域直接参与了观察到的现象。
