Inoue K, Motozaki A, Takeuchi Y, Nishimura M, Hara-Nishimura I
Department of Cell Biology, National Institute of Basic Biology, Okazaki, Japan.
Plant J. 1995 Feb;7(2):235-43. doi: 10.1046/j.1365-313x.1995.7020235.x.
During the post-germination growth of seeds, protein bodies fuse with one another and are converted to a central vacuole. To investigate this transition, protein-body membranes from dry seeds of pumpkin (Cucurbita sp.) were prepared and their protein components characterized. Five major proteins (designated MP23, MP27, MP28, MP32 and MP73) were detected in the protein-body membranes. A cDNA clone encoding both MP27 and MP32 has been isolated. The deduced precursor polypeptide was composed of a hydrophobic signal sequence, MP27 and MP32, in that order. A putative site of cleavage between MP27 and MP32 was located on the COOH-terminal side of asparagine 278, an indication that the post-translational cleavage may occur by the action of a vacuolar processing enzyme that converts proprotein precursors of seed proteins into the mature forms. Immunoelectron microscopic analysis showed that MP27 and MP32 were associated with protein-body membrane of dry pumpkin seeds. Among the five membrane proteins, MP27 and MP32 disappeared most rapidly during seedling growth. The degradation of MP27 and MP32 starts just after seed germination and proceeds in parallel with the transformation of the protein bodies into a vacuole.
在种子萌发后的生长过程中，蛋白体相互融合并转化为中央液泡。为了研究这一转变过程，制备了南瓜（南瓜属）干种子的蛋白体膜，并对其蛋白质成分进行了表征。在蛋白体膜中检测到了五种主要蛋白质（分别命名为MP23、MP27、MP28、MP32和MP73）。已分离出一个编码MP27和MP32的cDNA克隆。推导的前体多肽依次由一个疏水信号序列、MP27和MP32组成。MP27和MP32之间的一个假定切割位点位于天冬酰胺278的COOH末端一侧，这表明翻译后切割可能是由一种液泡加工酶的作用引起的，该酶将种子蛋白的前体蛋白转化为成熟形式。免疫电子显微镜分析表明，MP27和MP32与南瓜干种子的蛋白体膜相关。在这五种膜蛋白中，MP27和MP32在幼苗生长过程中消失得最快。MP27和MP32的降解在种子萌发后立即开始，并与蛋白体向液泡的转化同时进行。
