Yang Lu, Scarlata Suzanne
From the Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609.
From the Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
J Biol Chem. 2017 Mar 3;292(9):3779-3788. doi: 10.1074/jbc.M116.768499. Epub 2017 Jan 17.
Caveolae are protein-dense plasma membrane domains structurally composed of caveolin-1 or -3 along with other proteins. Our previous studies have shown that caveolae enhance calcium signals generated through the Gα/phospholipase Cβ signaling pathway and that subjecting cells to hypo-osmotic stress reverses this enhancement. In this study, we have used super-resolution fluorescence microscopy supplemented by fluorescence correlation studies to determine the structural factors that underlie this behavior. We find similar and significant population of Gα and one of its receptors, bradykinin type 2 receptor (B2R), as well as a significant population of Gα and its coupled β2-adrenergic receptor (βAR), are localized to caveola domains. Although mild osmotic stress deforms caveolae and alters interactions between the caveolae and these proteins, the general structure and the localization of caveola components remain largely unchanged. This deformation eliminates the ability of caveolae to stabilize calcium signals mediated through Gα-B2R, but does not affect cAMP signals mediated through Gα and βAR. Structurally, we find that mild osmotic stress corresponding roughly to a pressure of 3.82 newtons/m increases the domain diameter by ∼30% and increases the fluorescence intensity in the center of the domain mouth suggesting a flattening of the invagination. Approximate calculations show that caveolae in muscle tissue have the strength to handle the stress of muscle movement.
小窝是富含蛋白质的质膜结构域，由小窝蛋白-1或-3以及其他蛋白质构成。我们之前的研究表明，小窝可增强通过Gα/磷脂酶Cβ信号通路产生的钙信号，而使细胞遭受低渗应激会逆转这种增强作用。在本研究中，我们使用了超分辨率荧光显微镜并辅以荧光相关研究，以确定这种行为背后的结构因素。我们发现，Gα及其一种受体缓激肽2型受体（B2R）的相似且显著的群体，以及Gα及其偶联的β2-肾上腺素能受体（βAR）的显著群体，都定位于小窝结构域。尽管轻度渗透应激会使小窝变形并改变小窝与这些蛋白质之间的相互作用，但小窝成分的总体结构和定位基本保持不变。这种变形消除了小窝稳定通过Gα-B2R介导的钙信号的能力，但不影响通过Gα和βAR介导的cAMP信号。在结构上，我们发现大致相当于3.82牛顿/米压力的轻度渗透应激使结构域直径增加了约30%，并增加了结构域口中心的荧光强度，这表明内陷变平。近似计算表明，肌肉组织中的小窝有能力承受肌肉运动的压力。
