Li C P, Larkins B A
Department of Plant Sciences, University of Arizona, Tucson, 85721, USA.
Plant Mol Biol. 1996 Mar;30(5):873-82. doi: 10.1007/BF00020800.
A maize protein disulfide isomerase (PDI, EC 5.3.4.1) cDNA clone was isolated and characterized. The deduced amino acid sequence contains two regions characteristic of the active sites for PDI and a carboxyl-terminal endoplasmic reticulum (ER) retention sequence, Lys-Asp-Glu-Leu. Southern blot analysis indicated the maize PDI is encoded by a single gene that maps to the short arm of chromosome 4. When isolated from the cisternal and protein body ER, the PDI protein resolves into a fast and a slow form on SDS-PAGE. During endosperm development, the PDI RNA level increases between 10 and 14 days after pollination. In floury-2 (fl2) endosperm, which contains an abnormally processed alpha-zein protein, PDI expression is significantly increased, and the level of PDI protein and RNA is positively correlated with the dosage of fl2 alleles. The increase of PDI in fl2 occurs mainly in the cisternal ER fraction, whereas the most dramatic increase of binding protein (BiP) is in the protein body ER. We propose that the induction of PDI in the fl2 mutant reflects its role as a molecular chaperone, and that PDI functions in concert with BiP at different stages of zein processing and assembly into protein bodies.
分离并鉴定了一个玉米蛋白二硫键异构酶（PDI，EC 5.3.4.1）cDNA克隆。推导的氨基酸序列包含两个PDI活性位点的特征区域以及一个羧基末端内质网（ER）滞留序列，即赖氨酸-天冬氨酸-谷氨酸-亮氨酸。Southern杂交分析表明，玉米PDI由一个单基因编码，该基因定位于4号染色体的短臂上。当从潴泡和蛋白体ER中分离时，PDI蛋白在SDS-PAGE上可分离为快速和慢速两种形式。在胚乳发育过程中，授粉后10至14天PDI RNA水平升高。在含有异常加工的α-玉米醇溶蛋白的粉质-2（fl2）胚乳中，PDI表达显著增加，并且PDI蛋白和RNA的水平与fl2等位基因的剂量呈正相关。fl2中PDI的增加主要发生在潴泡ER部分，而结合蛋白（BiP）最显著的增加发生在蛋白体ER中。我们提出，fl2突变体中PDI的诱导反映了其作为分子伴侣的作用，并且PDI在玉米醇溶蛋白加工和组装成蛋白体的不同阶段与BiP协同发挥作用。
