The Turtle protein could act as a signaling receptor or function as a membrane-bound ligand for an unknown receptor. Alternatively, the Turtle protein could function as a co-receptor in a multi-protein receptor complex. Earlier work on the function of Bmtutl-519 suggested that it may act as a cell surface receptor or as a regulatory factor in the infection process of Nosema bombycis. To further investigate the function of Bmtutl-519 in the process of microsporidian infection and the possible regulatory pathways involved, we performed yeast two-hybrid screening on a silkworm midgut cDNA library and identified a Bombyx mori extensin-like protein/BmELP as a binding partner of Bmtutl-519. The interaction between Bmtutl-519 and BmELP was verified by GST pull-down and co-immunoprecipitation assays. Quantitative RT-PCR analysis showed that BmELP was commonly expressed in all of the examined tissues of the silkworm, and the expression was highest in the head. Moreover, BmELP was expressed throughout the entire development period, and the lowest levels of expression were observed at the egg stage. The results of infection experiments showed that N. bombycis infection caused the up-regulation of BmELP expression, especially in vitro. Taken together, our findings may provide new insights into the roles of BmELP and Bmtutl-519 in microsporidian infection.

Turtle 蛋白可以作为信号受体或作为未知受体的膜结合配体。或者，海龟蛋白可以作为多蛋白受体复合物中的共受体。早期对 Bmtutl-519 功能的研究表明，它可能作为细胞表面受体或在Nosema bombycis感染过程中作为调节因子。为了进一步研究 Bmtutl-519 在微孢子虫感染过程中的功能和可能涉及的调控途径，我们对家蚕中肠 cDNA 文库进行了酵母双杂交筛选，并鉴定了家蚕延伸蛋白样蛋白/BmELP 作为 Bmtutl-519 的结合伴侣。Bmtutl-519 和 BmELP 之间的相互作用通过 GST pull-down 和免疫共沉淀试验进行了验证。定量RT-PCR分析表明，BmELP在家蚕所有组织中普遍表达，以头部表达最高。此外，BmELP 在整个发育期都有表达，在卵期观察到最低水平的表达。感染实验结果表明，N. bombycis感染引起BmELP 表达上调，尤其是在体外。总之，我们的发现可能为 BmELP 和 Bmtutl-519 在微孢子虫感染中的作用提供新的见解。