Function of lipid transfer protein and its homologus proteins in plant cells

1.脂质转运蛋白（LTP）及其同源蛋白的功能LPT是一种在体外能够在生物膜间转运极性脂质的蛋白质，但在体内不可能参与细胞内的脂质转运。LTP不发生在细胞质中，但在细胞和细胞壁的密度囊泡。LTP基因在胚、胚乳、叶原基和花原基等发育器官的表面积中表达和积累。此外，LTP具有结合脂肪酸和酰基辅酶A的能力。从这些结果。LTP似乎在体内作为蜡或角质单体的载体起作用。这一假设得到了以下证据的支持，即紫外线照射诱导黄瓜叶片中蜡的合成，随后是LTP在黄瓜叶片中的积累。另一方面，LTP在蓖麻子子叶细胞中密度囊泡中的定位以及这些密度囊泡组装成液泡的问题尚未解决. LTP基因及其同源蛋白基因的克隆在蓖麻幼苗中存在器官特异性的LTP亚型A-D。我们用PCR方法克隆了C _cDNA亚型基因，确定了C _cDNA亚型基因的内含子结构，但由于LTP基因上游区的分离不成功，未能确定其启动子结构。从蓖麻子叶基因组文库中分离到几个克隆，核苷酸序列分析正在进行中，LTP序列中有8个半胱氨酸保守。为了检查这些半胱氨酸对于LTP与脂肪酸结合的作用，将同种型C _cDNA修饰以产生具有丝氨酸而不是半胱氨酸的同种型C，并且现在表达修饰的LTP。

1. Function of lipid transfer protein (LTP) and its homologus proteinsLPT was isolated as a protein which transfers polar lipids between biomembranes in vitro, but it is unlikely that LTP functions in vivo for intracellular lipid trasfer. LTPs did not occur in cytosol but in density vesicles in cells and cell walls. The expression of LTP genes and the accumulation of LTPs were observed in the surface area of developing organs such as embryos, endosperms and primordia of leaves and floweres. In addition, LTPs have the capacities of binding fatty acids and acylCoAs. From these results. LTP seems to functions in vivo as a carrier of wax or cutin monomers. This assumption was supported by evidence that wax synthesis induced by UV irradiation in cucmber leaves was followed by the accumulation of LTPs in the cuticles. On the other hand , the localization of LTPs in density vesicles in castor bean cotyledon cells and assembly of these vesicles into a vacuoles remains unsolved.2. Cloning of LTP genes and its homologus protein genesThere are organ-specific isoforms of LTP, A - D, in castor bean seedlings. We cloned the isoform C gene by PCR method using the isoform C _cDNA.Intron sturucture of the isoform C gene has been determined, but its promoter structure has not, because of unsuccessfulness in isolating the upstream region of LTP gene. Several clones have been isolated from genomic library prepared from castor bean cotyledons and the analysis of nucleotides is in progress.Eight cysteines in LTP sequence were conservative. To examine the role of these cysteines for binding of LTP to fatty acid, the isoform C _cDNA was modified to yield the isoform C with serines instead the cysteines and the modified LTP is now to be expressed.