Guenoune Dana, Landau Serge, Amir Rachel, Badani Hana, Devash Levana, Wolf Shmuel, Galili Shmuel
Department of Agronomy and Natural Resources, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel.
J Agric Food Chem. 2002 Apr 10;50(8):2256-60. doi: 10.1021/jf010949k.
Soybean vegetative storage proteins (S-VSPs) are lysine-rich and, hence, are potentially of high nutritive value for high productive ruminants. Using S-VSPs from wild-type soybean and from transgenic tobacco plants expressing either one of the two S-VSPs subunits (S-VSP alpha or S-VSP beta) or both, we tested their stability in cow rumen fluid under in situ conditions, using SDS-polyacrylamide gel electrophoresis. Proteolysis and degradation pattern of S-VSPs from transgenic tobacco leaves occurred relatively fast compared with that of wild-type (WT) soybean plants. Comparing the two S-VSPs subunits expressed in transgenic plants, we found that S-VSP alpha was degraded much faster than S-VSP beta. The degradation pattern of S-VSPs in transgenic tobacco plants expressing both subunits resembled that of WT soybean. In contrast, the degradation pattern of transgenic tobacco plants expressing a single subunit was different. These finding suggest that the quaternary structure of S-VSPs may be an important factor determining their resistance to rumen degradation. Our results also suggest that the stability to rumen proteolysis of a given protein, when expressed in a transgenic plant, may not always be predictable and has to be verified.
大豆营养贮藏蛋白（S-VSPs）富含赖氨酸，因此对高产反刍动物可能具有很高的营养价值。我们使用来自野生型大豆以及表达两种S-VSPs亚基（S-VSPα或S-VSPβ）之一或两者的转基因烟草植物中的S-VSPs，通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳，在原位条件下测试了它们在牛瘤胃液中的稳定性。与野生型（WT）大豆植物相比，转基因烟草叶片中S-VSPs的蛋白水解和降解模式发生得相对较快。比较转基因植物中表达的两种S-VSPs亚基，我们发现S-VSPα的降解速度比S-VSPβ快得多。在同时表达两个亚基的转基因烟草植物中，S-VSPs的降解模式与野生型大豆相似。相反，表达单个亚基的转基因烟草植物的降解模式则不同。这些发现表明，S-VSPs的四级结构可能是决定其对瘤胃降解抗性的一个重要因素。我们的结果还表明，当在转基因植物中表达时，给定蛋白质对瘤胃蛋白水解的稳定性可能并不总是可预测的，必须进行验证。
