Department of Genetics, Yale School of Medicine, New Haven, CT 06520-8005.
Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536-0812.
Proc Natl Acad Sci U S A. 2023 Oct 17;120(42):e2307721120. doi: 10.1073/pnas.2307721120. Epub 2023 Oct 11.
The activity of proteins is thought to be invariably determined by their amino acid sequence or composition, but we show that a long segment of a viral protein can support infection independent of its sequence or composition. During virus entry, the papillomavirus L2 capsid protein protrudes through the endosome membrane into the cytoplasm to bind cellular factors such as retromer required for intracellular virus trafficking. Here, we show that an ~110 amino acid segment of L2 is predicted to be disordered and that large deletions in this segment abolish infectivity of HPV16 pseudoviruses by inhibiting cytoplasmic protrusion of L2, association with retromer, and proper virus trafficking. The activity of these mutants can be restored by insertion of protein segments with diverse sequences, compositions, and chemical properties, including scrambled amino acid sequences, a tandem array of a short sequence, and the intrinsically disordered region of an unrelated cellular protein. The infectivity of mutants with small in-frame deletions in this segment directly correlates with the size of the segment. These results indicate that the length of the disordered segment, not its sequence or composition, determines its activity during HPV16 pseudovirus infection. We propose that a minimal length of L2 is required for it to protrude far enough into the cytoplasm to bind cytoplasmic trafficking factors, but the sequence of this segment is largely irrelevant. Thus, protein segments can carry out complex biological functions such as Human papillomavirus pseudovirus infection in a sequence-independent manner. This finding has important implications for protein function and evolution.
蛋白质的活性被认为始终取决于其氨基酸序列或组成，但我们表明，病毒蛋白的长片段可以独立于其序列或组成支持感染。在病毒进入过程中，乳头瘤病毒 L2 衣壳蛋白穿过内体膜突入细胞质，以结合细胞因子，如内体逆向转运所需的 retromer ，用于细胞内病毒运输。在这里，我们表明，L2 的一个约 110 个氨基酸的片段预计是无规的，并且该片段中的大缺失通过抑制 L2 的细胞质突出、与 retromer 的结合和适当的病毒运输，消除了 HPV16 假病毒的感染性。这些突变体的活性可以通过插入具有不同序列、组成和化学性质的蛋白片段来恢复，包括氨基酸序列的乱序、短序列的串联阵列和无关联的细胞蛋白的无规区。该片段中的小框内缺失突变体的感染性与片段的大小直接相关。这些结果表明，在 HPV16 假病毒感染过程中，无规片段的长度而不是其序列或组成决定了其活性。我们提出，L2 的无规片段需要有足够的长度才能突入细胞质足够远，以结合细胞质运输因子，但该片段的序列在很大程度上是无关紧要的。因此，蛋白片段可以以序列独立的方式执行复杂的生物学功能，如人乳头瘤病毒假病毒感染。这一发现对蛋白质功能和进化具有重要意义。
