Ciuraszkiewicz Justyna, Olczak Mariusz, Watorek Wiesław
Laboratory of Biochemistry, Faculty of Biotechnology, University of Wroclaw, Wrocław, Poland.
Acta Biochim Pol. 2007;54(1):175-82. Epub 2007 Mar 9.
Transferrins play a major role in iron homeostasis and metabolism. In vertebrates, these proteins are synthesised in the liver and dispersed within the organism by the bloodstream. In oviparous vertebrates additional expression is observed in the oviduct and the synthesised protein is deposited in egg white as ovotransferrin. Most research on ovotransferrin has been performed on the chicken protein. There is a limited amount of information on other bird transferrins, and until our previous paper on red-eared turtle protein there was no data on the isolation, sequencing and biochemical properties of reptilian ovotransferrins. Recently our laboratory deposited ten new sequences of reptilian transferrins in the EMBL database. A comparative analysis of these sequences indicates a possibility of different mechanisms of iron release among crocodile and snake transferrin. In the present paper we follow with the purification and analysis of the basic biochemical properties of two crocodile (Crocodilus niloticus, C. rhombifer) and one snake (Python molurus bivittatus) ovotransferrins. The proteins were purified by anion exchange and hydrophobic chromatography, and their N-terminal amino-acid sequences, molecular mass and isoelectric points were determined. All three proteins are glycosylated and their N-glycan chromatographic profiles show the largest contribution of neutral oligosaccharides in crocodile and disialylated glycans in python ovotransferrin. The absorption spectra of iron-saturated transferrins were analysed. Iron release from these proteins is pH-dependent, showing a biphasic character in crocodile ovotransferrins and a monophasic type in the python protein. The reason for the different types of iron release is discussed.
转铁蛋白在铁稳态和代谢中起主要作用。在脊椎动物中,这些蛋白质在肝脏中合成,并通过血液循环在体内分布。在卵生脊椎动物中,在输卵管中观察到额外的表达,合成的蛋白质作为卵转铁蛋白沉积在蛋清中。大多数关于卵转铁蛋白的研究是针对鸡的蛋白质进行的。关于其他鸟类转铁蛋白的信息有限,在我们之前关于红耳龟蛋白质的论文发表之前,没有关于爬行动物卵转铁蛋白的分离、测序和生化特性的数据。最近,我们实验室在EMBL数据库中存入了十个新的爬行动物转铁蛋白序列。对这些序列的比较分析表明,鳄鱼和蛇的转铁蛋白之间可能存在不同的铁释放机制。在本文中,我们接着对两种鳄鱼(尼罗鳄、菱斑鳄)和一种蛇(缅甸蟒)的卵转铁蛋白进行纯化,并分析其基本生化特性。通过阴离子交换和疏水色谱法纯化蛋白质,并测定其N端氨基酸序列、分子量和等电点。所有三种蛋白质都进行了糖基化,其N-聚糖色谱图谱显示,中性寡糖在鳄鱼卵转铁蛋白中贡献最大,而双唾液酸化聚糖在缅甸蟒卵转铁蛋白中贡献最大。分析了铁饱和转铁蛋白的吸收光谱。这些蛋白质的铁释放依赖于pH值,在鳄鱼卵转铁蛋白中呈双相特征,在缅甸蟒蛋白质中呈单相类型。讨论了不同类型铁释放的原因。