Yoshiga T, Hernandez V P, Fallon A M, Law J H
The Department of Biochemistry and the Center for Insect Science, University of Arizona, Tucson, AZ 85721, USA.
Proc Natl Acad Sci U S A. 1997 Nov 11;94(23):12337-42. doi: 10.1073/pnas.94.23.12337.
When treated with heat-killed bacterial cells, mosquito cells in culture respond by up-regulating several proteins. Among these is a 66-kDa protein (p66) that is secreted from cells derived from both Aedes aegypti and Aedes albopictus. p66 was degraded by proteolysis and gave a virtually identical pattern of peptide products for each mosquito species. The sequence of one peptide (31 amino acids) was determined and found to have similarity to insect transferrins. By using conserved regions of insect transferrin sequences, degenerate oligonucleotide PCR primers were designed and used to isolate a cDNA clone encoding an A. aegypti transferrin. The encoded protein contained a signal sequence that, when cleaved, would yield a mature protein of 68 kDa. It contained the 31-amino acid peptide, and the 3' end exactly matched a cDNA encoding a polypeptide that is up-regulated when A. aegypti encapsulates filarial worms [Beerntsen, B. T., Severson, D. W. & Christensen, B. M. (1994) Exp. Parasitol. 79, 312-321]. This transferrin, like those of two other insect species, has conserved iron-binding residues in the N-terminal lobe but not in the C-terminal lobe, which also has large deletions in the polypeptide chain, compared with transferrins with functional C-terminal lobes. The hypothesis is developed that this transferrin plays a role similar to vertebrate lactoferrin in sequestering iron from invading organisms and that degradation of the structure of the C-terminal lobe might be a mechanism for evading pathogens that elaborate transferrin receptors to tap sequestered iron.
用热灭活的细菌细胞处理时，培养中的蚊子细胞会通过上调几种蛋白质做出反应。其中有一种66 kDa的蛋白质（p66），它由埃及伊蚊和白纹伊蚊来源的细胞分泌。p66经蛋白水解作用降解，并且每种蚊子产生的肽产物模式几乎相同。测定了一个肽段（31个氨基酸）的序列，发现它与昆虫转铁蛋白有相似性。利用昆虫转铁蛋白序列的保守区域，设计了简并寡核苷酸PCR引物，并用于分离编码埃及伊蚊转铁蛋白的cDNA克隆。编码的蛋白质含有一个信号序列，切割后会产生一个68 kDa的成熟蛋白。它包含31个氨基酸的肽段，其3'端与编码一种在埃及伊蚊包裹丝虫时上调的多肽的cDNA完全匹配[Beerntsen, B. T., Severson, D. W. & Christensen, B. M. (1994) Exp. Parasitol. 79, 312 - 321]。与其他两种昆虫的转铁蛋白一样，这种转铁蛋白在N端叶中有保守的铁结合残基，但在C端叶中没有，与具有功能性C端叶的转铁蛋白相比，其多肽链中也有大量缺失。由此提出一个假说，即这种转铁蛋白在从入侵生物体中螯合铁方面发挥着与脊椎动物乳铁蛋白类似的作用，并且C端叶结构的降解可能是一种逃避病原体的机制，这些病原体精心制作转铁蛋白受体来获取螯合的铁。
