Gong Jing, Hou Yong, Zha Xing-Fu, Lu Cheng, Zhu Yong, Xia Qing-You
Key Sericultural Laboratory of Agricultural Ministry, Southwest University, Chongqing 400715, People's Republic of China.
DNA Seq. 2006 Oct;17(5):326-33. doi: 10.1080/10425170600886706.
Cholesterol transport is a very important process in insect. We have isolated the Bombyx mori sterol carrier protein x (BmSCPx) cDNA and sterol carrier protein 2 (BmSCP2) cDNA: a 1.7 kb clone encoding SCPx, a 3-ketoacyl CoA thiolase, and 0.6 kb clone presumably encoding SCP2, which is thought to be an intracellular lipid transfer protein. Interestingly, the identical gene SCPx/SCP2 encodes the two types of transcripts by alternative splicing mechanism in Bombyx mori. The SCPx mRNA spans two exons in genome, and conceptual translation of the SCPx cDNA encodes a protein of 536 amino acids, which contains a thiolase domain and a SCP2 domain. Whereas the SCP2 mRNA partly lakes the first exon, and the SCP2 is a 146 amino acids containing a SCP2 domain only. Both BmSCPx and BmSCP2 have a putative peroxisomal targeting signal in the C-terminal region. BmSCPx shares 94 and 72% similarity to Spodoptera littoralis SCPx and human SCPx, respectively. RT-PCR analysis reveals that transcripts of BmSCP2 were detected in all tissues analyzed. BmSCPx transcription expressed only in midgut and malpighian tubules. However, the BmSCPx and BmSCP2 express strong in midgut during the last instar larvae. The tissue-specific expression pattern of BmSCPx and BmSCP2 is consistent with a role for these proteins in cholesterol metabolism. The results suggest that SCPx/SCP2 may play a key role in sterol absorption and intracellular carrier in silkworm.
胆固醇转运是昆虫体内一个非常重要的过程。我们已经分离出了家蚕固醇载体蛋白x（BmSCPx）的cDNA和固醇载体蛋白2（BmSCP2）的cDNA：一个1.7 kb的克隆编码SCPx，一种3-酮酰基辅酶A硫解酶，以及一个0.6 kb的克隆，推测编码SCP2，SCP2被认为是一种细胞内脂质转运蛋白。有趣的是，在家蚕中，相同的基因SCPx/SCP2通过可变剪接机制编码两种类型的转录本。SCPx mRNA在基因组中跨越两个外显子，SCPx cDNA的概念性翻译编码一个536个氨基酸的蛋白质，该蛋白质包含一个硫解酶结构域和一个SCP2结构域。而SCP2 mRNA部分缺失第一个外显子，SCP2是一个仅含146个氨基酸且只包含一个SCP2结构域的蛋白。BmSCPx和BmSCP2在C末端区域都有一个假定的过氧化物酶体靶向信号。BmSCPx与斜纹夜蛾SCPx和人类SCPx的相似性分别为94%和72%。RT-PCR分析表明，在所有分析的组织中都检测到了BmSCP2的转录本。BmSCPx转录仅在中肠和马氏管中表达。然而，在末龄幼虫阶段，BmSCPx和BmSCP2在中肠中表达强烈。BmSCPx和BmSCP2的组织特异性表达模式与这些蛋白质在胆固醇代谢中的作用一致。结果表明，SCPx/SCP2可能在蚕的固醇吸收和细胞内载体方面发挥关键作用。
