Department of Chemistry & Biochemistry, University of California San Diego, La Jolla, CA, United States of America.
PLoS One. 2019 Jan 10;14(1):e0205618. doi: 10.1371/journal.pone.0205618. eCollection 2019.
Diversity-generating retroelements (DGRs) are widely distributed in bacteria, archaea, and microbial viruses, and bring about unparalleled levels of sequence variation in target proteins. While DGR variable proteins share low sequence identity, the structures of several such proteins have revealed the C-type lectin (CLec)-fold as a conserved scaffold for accommodating massive sequence variation. This conservation has led to the suggestion that the CLec-fold may be useful in molecular surface display applications. Thermostability is an attractive feature in such applications, and thus we studied the variable protein of a DGR encoded by a prophage of the thermophile Thermus aquaticus. We report here the 2.8 Å resolution crystal structure of the variable protein from the T. aquaticus DGR, called TaqVP, and confirm that it has a CLec-fold. Remarkably, its variable region is nearly identical in structure to those of several other CLec-fold DGR variable proteins despite low sequence identity among these. TaqVP was found to be thermostable, which appears to be a property shared by several CLec-fold DGR variable proteins. These results provide impetus for the pursuit of the DGR variable protein CLec-fold in molecular display applications.
多样性产生的 retroelements（DGRs）广泛分布于细菌、古菌和微生物病毒中，为目标蛋白带来了无与伦比的序列变异水平。虽然 DGR 可变蛋白的序列同一性较低，但几种此类蛋白的结构揭示了 C 型凝集素（CLec）-折叠作为容纳大量序列变异的保守支架。这种保守性导致了 CLec-折叠可能在分子表面展示应用中有用的假设。热稳定性是此类应用中的一个吸引人的特征，因此我们研究了一种由嗜热菌 Thermus aquaticus 的噬菌体编码的 DGR 的可变蛋白。我们在这里报告了来自 T. aquaticus DGR 的可变蛋白 TaqVP 的 2.8 Å 分辨率晶体结构，并证实它具有 CLec-折叠。值得注意的是，尽管这些蛋白之间的序列同一性较低，但它的可变区在结构上与其他几个 CLec-折叠 DGR 可变蛋白非常相似。发现 TaqVP 具有热稳定性，这似乎是几个 CLec-折叠 DGR 可变蛋白共有的特性。这些结果为在分子展示应用中追求 DGR 可变蛋白 CLec-折叠提供了动力。
