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Abstract：
The Lyme disease spirochete Borrelia burgdorferi is unique among bacteria in its large number of lipoproteins that are encoded by a small, exceptionally fragmented, and predominantly linear genome. Peripherally anchored in either the inner or outer membrane and facing either the periplasm or the external environment, these lipoproteins assume varied roles. A prominent subset of lipoproteins functioning as the apparent linchpins of the enzootic tick-vertebrate infection cycle have been explored as vaccine targets. Yet, most of the B. burgdorferi lipoproteome has remained uncharacterized. Here, we comprehensively and conclusively localize the B. burgdorferi lipoproteome by applying established protein localization assays to a newly generated epitope-tagged lipoprotein expression library and by validating the obtained individual protein localization results using a sensitive global mass spectrometry approach. The derived consensus localization data indicate that 86 of the 125 analyzed lipoproteins encoded by B. burgdorferi are secreted to the bacterial surface. Thirty-one of the remaining 39 periplasmic lipoproteins are retained in the inner membrane, with only 8 lipoproteins being anchored in the periplasmic leaflet of the outer membrane. The localization of 10 lipoproteins was further defined or revised, and 52 surface and 23 periplasmic lipoproteins were newly localized. Cross-referencing prior studies revealed that the borrelial surface lipoproteome contributing to the host-pathogen interface is encoded predominantly by plasmids. Conversely, periplasmic lipoproteins are encoded mainly by chromosomal loci. These studies close a gap in our understanding of the functional lipoproteome of an important human pathogen and set the stage for more in-depth studies of thus-far-neglected spirochetal lipoproteins.IMPORTANCE The small and exceptionally fragmented genome of the Lyme disease spirochete Borrelia burgdorferi encodes over 120 lipoproteins. Studies in the field have predominantly focused on a relatively small number of surface lipoproteins that play important roles in the transmission and pathogenesis of this global human pathogen. Yet, a comprehensive spatial assessment of the entire borrelial lipoproteome has been missing. The current study newly identifies 52 surface and 23 periplasmic lipoproteins. Overall, two-thirds of the B. burgdorferi lipoproteins localize to the surface, while outer membrane lipoproteins facing the periplasm are rare. This analysis underscores the dominant contribution of lipoproteins to the spirochete\'s rather complex and adaptable host-pathogen interface, and it encourages further functional exploration of its lipoproteome.
摘要：
莱姆病螺旋体伯氏螺旋体在细菌中是独一无二的，其大量的脂蛋白由一个小的编码，异常分散，主要是线性基因组。外周固定在内膜或外膜中，面向周质或外部环境，这些脂蛋白承担不同的作用。已经探索了作为植物性蜱-脊椎动物感染周期的明显关键的脂蛋白的一个突出子集作为疫苗靶标。然而，大多数伯氏芽孢杆菌脂蛋白组仍未表征。这里,我们通过将已建立的蛋白质定位测定应用于新产生的表位标记的脂蛋白表达文库,并通过使用敏感的全局质谱方法验证获得的单个蛋白质定位结果,全面而最终地定位了伯氏芽孢杆菌脂蛋白组.衍生的共有定位数据表明，由伯氏芽孢杆菌编码的125种分析的脂蛋白中有86种被分泌到细菌表面。其余39个周质脂蛋白中有31个保留在内膜中，只有8种脂蛋白锚定在外膜的周质小叶中。进一步定义或修订了10种脂蛋白的定位，新定位了52种表面脂蛋白和23种周质脂蛋白。交叉引用先前的研究表明，有助于宿主-病原体界面的疏螺旋体表面脂蛋白组主要由质粒编码。相反，周质脂蛋白主要由染色体位点编码。这些研究缩小了我们对重要人类病原体的功能性脂蛋白组的理解的差距，并为迄今为止被忽视的螺旋体脂蛋白的更深入研究奠定了基础。重要性莱姆病螺旋体伯氏螺旋体的小且异常片段化的基因组编码超过120种脂蛋白。该领域的研究主要集中在相对少量的表面脂蛋白上，这些脂蛋白在这种全球人类病原体的传播和发病机理中起着重要作用。然而，缺乏对整个螺旋体脂蛋白组的全面空间评估.目前的研究新鉴定了52个表面和23个周质脂蛋白。总的来说,三分之二的B.burgdorferi脂蛋白位于表面，而面对周质的外膜脂蛋白很少见。该分析强调了脂蛋白对螺旋体相当复杂和适应性强的宿主-病原体界面的主要贡献。并鼓励对其脂蛋白组进行进一步的功能探索。
