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蛋白激酶A(PKA)是由1个调节亚基(R亚基)二聚体和两个催化亚基(C亚基)组成的四聚体,全酶无活性。R亚基有RⅠα、RⅠβ、RⅡα和RⅡβ4种亚型,分别具有不同的理化性质。RⅡβ亚基氨基端包含1个二聚化/对接结构域,PKA通过此结构域与腺苷酸激酶锚定蛋白结合锚定于细胞的特定位点。羧基端是两个串联的高度保守的环核苷酸结构域,与PKA全酶解聚以及激活有关。两个RC异二聚体通过RⅡβ亚基中的β4~β5环相锚定。细胞质中存在足够的Mg ATP时将导致RⅡβ亚基自身磷酸化。RⅡβ在特定组织表达,主要表达于内分泌腺、脑和脂肪组织。生物信息学分析表明,RⅡβ与其他R亚基的序列有很大差别,只有大约50%的序列相同,提示RⅡβ可能具有不同的生物学功能。因此,目前对PKA RⅡβ的功能及其作用机制的研究已逐渐成为热点。
Protein kinase A (PKA) is a tetramer composed of one regulatory subunit (R subunit) dimer and two catalytic subunits (C subunit), which are inactive. R subunits R Ⅰ α, R Ⅰ β, R Ⅱ α and R Ⅱ β 4 subtypes, respectively, with different physicochemical properties. The amino terminus of the RIIbeta subunit contains a dimerization / docking domain through which PKA binds to adenylate kinase-anchored proteins anchored to specific sites in the cell. The carboxy terminus is a concatenation of two highly conserved cyclic nucleotide domains that are involved in PKA homolytic polymerization and activation. Two RC heterodimers are anchored by the [beta] 4- [beta] 5 ring in the RII [beta] subunit. The presence of sufficient Mg ATP in the cytoplasm will result in autophosphorylation of the RII beta subunit. R Ⅱ β is expressed in specific tissues and is mainly expressed in endocrine glands, brain and adipose tissue. Bioinformatics analysis showed that there was a great difference between RIIβ and other R subunits. Only about 50% of the sequences had the same sequence, suggesting that RⅡβ may have different biological functions. Therefore, the current research on the function and mechanism of PKA RⅡβ has become a hot spot.