Interferon-regulated myxovirus resistance protein B (MxB) is an interferon-induced GTPase belonging to the dynamin superfamily. It inhibits infection with a wide range of different viruses, including HIV-1, by impairing viral DNA entry into the nucleus. Unlike the related antiviral GTPase MxA, MxB possesses an N-terminal region that contains a nuclear localization signal and is crucial for inhibiting HIV-1. Because MxB previously has been shown to reside in both the nuclear envelope and the cytoplasm, here we used bioinformatics and biochemical approaches to identify a nuclear export signal (NES) responsible for MxB's cytoplasmic location. Using the online computational tool LocNES (Locating Nuclear Export Signals or NESs), we identified five putative NES candidates in MxB and investigated whether their deletion caused nuclear localization of MxB. Our results revealed that none of the five deletion variants relocates to the nucleus, suggesting that these five predicted NES sequences do not confer NES activity. Interestingly, deletion of one sequence, encompassing amino acids 505-527, abrogated the anti-HIV-1 activity of MxB. Further mutation experiments disclosed that amino acids 515-519, and Pro-515 in particular, regulate MxB oligomerization and its binding to HIV-1 capsid, thereby playing an important role in MxB-mediated restriction of HIV-1 infection. In summary, our results indicate that none of the five predicted NES sequences in MxB appears to be required for its nuclear export. Our findings also reveal several residues in MxB, including Pro-515, critical for its oligomerization and anti-HIV-1 function.

中文翻译：

---

dynamin样GTPase MxB的Pro-515通过调节MxB寡聚化并与HIV-1衣壳结合而有助于HIV-1抑制。

干扰素调节的粘液病毒抗性蛋白B（MxB）是一种干扰素诱导的GTPase，属于dynamin超家族。它通过削弱病毒DNA进入细胞核来抑制各种不同病毒（包括HIV-1）的感染。与相关的抗病毒GTPase MxA不同，MxB具有一个N末端区域，该区域包含一个核定位信号，对于抑制HIV-1至关重要。由于以前已证明MxB驻留在核膜和细胞质中，因此在这里我们使用生物信息学和生化方法来鉴定负责MxB胞质定位的核输出信号（NES）。使用在线计算工具LocNES（定位核出口信号或NESs），我们在MxB中确定了五个推定的NES候选基因，并调查了它们的缺失是否引起MxB的核定位。我们的结果表明，这五个缺失变体均未移至细胞核，这表明这五个预测的NES序列均未赋予NES活性。有趣的是，一个包含氨基酸505-​​527的序列的缺失消除了MxB的抗HIV-1活性。进一步的突变实验表明，氨基酸515-519和Pro-515特别调节MxB寡聚及其与HIV-1衣壳的结合，从而在MxB介导的HIV-1感染限制中起重要作用。总而言之，我们的结果表明，MxB的五个预测NES序列似乎都不要求其核出口。我们的发现还揭示了MxB中的一些残基，包括Pro-515，