Makarova Kira S, Wolf Yuri I, Karamycheva Svetlana, Koonin Eugene V
National Center for Biotechnology Information, National Library of Medicine, Bethesda, MD, United States.
Front Microbiol. 2021 Aug 18;12:721392. doi: 10.3389/fmicb.2021.721392. eCollection 2021.
Molecular mechanisms involved in biological conflicts and self vs nonself recognition in archaea remain poorly characterized. We apply phylogenomic analysis to identify a hypervariable gene module that is widespread among . These loci consist of an upstream gene coding for a large protein containing several immunoglobulin (Ig) domains and unique combinations of downstream genes, some of which also contain Ig domains. In the large Ig domain containing protein, the C-terminal Ig domain sequence is hypervariable, apparently, as a result of recombination between genes from different . To reflect the hypervariability, we denote this gene module VARTIG (VARiable IG). The overall organization of the VARTIG modules is similar to the organization of Polymorphic Toxin Systems (PTS). Archaeal genomes outside encode a variety of Ig domain proteins, but no counterparts to VARTIG and no Ig domains with comparable levels of variability. The specific functions of VARTIG remain unknown but the identified features of this system imply three testable hypotheses: (i) involvement in inter-microbial conflicts analogous to PTS, (ii) role in innate immunity analogous to the vertebrate complement system, and (iii) function in self vs nonself discrimination analogous to the vertebrate Major Histocompatibility Complex. The latter two hypotheses seem to be of particular interest given the apparent analogy to the vertebrate immunity.
古菌中生物冲突以及自我与非自我识别所涉及的分子机制仍未得到充分表征。我们应用系统发育基因组分析来鉴定一个在……中广泛存在的高变基因模块。这些基因座由一个上游基因和下游基因的独特组合组成，上游基因编码一种含有多个免疫球蛋白（Ig）结构域的大蛋白，下游基因中的一些也含有Ig结构域。在含有大Ig结构域的蛋白中，C末端Ig结构域序列高度可变，显然是由于来自不同……的基因之间的重组所致。为了反映这种高变性，我们将这个基因模块命名为VARTIG（可变免疫球蛋白）。VARTIG模块的整体组织与多态毒素系统（PTS）的组织相似。……之外的古菌基因组编码多种Ig结构域蛋白，但没有与VARTIG对应的蛋白，也没有具有可比变异性水平的Ig结构域。VARTIG的具体功能仍然未知，但该系统已确定的特征暗示了三个可检验的假设：（i）参与类似于PTS的微生物间冲突，（ii）在先天免疫中发挥类似于脊椎动物补体系统的作用，以及（iii）在自我与非自我区分中发挥类似于脊椎动物主要组织相容性复合体的功能。鉴于与脊椎动物免疫的明显类比，后两个假设似乎特别令人感兴趣。
