Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, USA.
Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado, USA.
Appl Environ Microbiol. 2019 Jan 23;85(3). doi: 10.1128/AEM.01983-18. Print 2019 Feb 1.
Genomes of extremely thermophilic species encode novel cellulose binding proteins, called tāpirins, located proximate to the type IV pilus locus. The C-terminal domain of tāpirin 0844 (Calkro_0844) is structurally unique and has a cellulose binding affinity akin to that seen with family 3 carbohydrate binding modules (CBM3s). Here, full-length and C-terminal versions of tāpirins from (Athe_1870), (Calhy_0908), (Calkr_0826), and (NA10_0869) were produced recombinantly in and compared to Calkro_0844. All five tāpirins bound to microcrystalline cellulose, switchgrass, poplar, and filter paper but not to xylan. Densitometry analysis of bound protein fractions visualized by SDS-PAGE revealed that Calhy_0908 and Calkr_0826 (from weakly cellulolytic species) associated with the cellulose substrates to a greater extent than Athe_1870, Calkro_0844, and NA10_0869 (from strongly cellulolytic species). Perhaps this relates to their specific needs to capture glucans released from lignocellulose by cellulases produced in communities. Calkro_0844 and NA10_0869 share a higher degree of amino acid sequence identity (>80% identity) with each other than either does with Athe_1870 (∼50%). The levels of amino acid sequence identity of Calhy_0908 and Calkr_0826 to Calkro_0844 were only 16% and 36%, respectively, although the three-dimensional structures of their C-terminal binding regions were closely related. Unlike the parent strain, mutants lacking the tāpirin genes did not bind to cellulose following short-term incubation, suggesting a role in cell association with plant biomass. Given the scarcity of carbohydrates in neutral terrestrial hot springs, tāpirins likely help scavenge carbohydrates from lignocellulose to support growth and survival of species. The mechanisms by which microorganisms attach to and degrade lignocellulose are important to understand if effective approaches for conversion of plant biomass into fuels and chemicals are to be developed. species grow on carbohydrates from lignocellulose at elevated temperatures and have biotechnological significance for that reason. Novel cellulose binding proteins, called tāpirins, are involved in the way that species interact with microcrystalline cellulose, and additional information about the diversity of these proteins across the genus, including binding affinity and three-dimensional structural comparisons, is provided here.
极度嗜热 物种的基因组编码新型纤维素结合蛋白，称为 tāpirins，位于 IV 型菌毛基因座附近。tāpirin 0844（Calkro_0844）的 C 端结构域结构独特，具有类似于家族 3 碳水化合物结合模块（CBM3s）的纤维素结合亲和力。在这里，来自 （Athe_1870）、 （Calhy_0908）、 （Calkr_0826）和 （NA10_0869）的全长和 C 端版本的 tāpirins 被在 中重组产生，并与 Calkro_0844 进行了比较。所有 5 种 tāpirins 均与微晶纤维素、柳枝稷、杨树和滤纸结合，但不与木聚糖结合。SDS-PAGE 可视化的结合蛋白部分的密度测定分析表明，Calhy_0908 和 Calkr_0826（来自弱纤维素分解菌）与纤维素底物的结合程度大于 Athe_1870、Calkro_0844 和 NA10_0869（来自强纤维素分解菌）。这也许与它们通过纤维素酶从木质纤维素中捕获葡聚糖的特定需求有关，这些纤维素酶是由 群落产生的。Calkro_0844 和 NA10_0869 彼此之间的氨基酸序列同一性（>80%同一性）高于与 Athe_1870 的同一性（约 50%）。Calhy_0908 和 Calkr_0826 与 Calkro_0844 的氨基酸序列同一性水平分别仅为 16%和 36%，尽管它们的三维结合区域结构非常相似。与亲本菌株不同的是，缺乏 tāpirin 基因的 突变体在短期孵育后不会与纤维素结合，这表明它们在与植物生物质的细胞关联中起作用。鉴于中性陆地温泉中碳水化合物的稀缺性，tāpirins 可能有助于从木质纤维素中清除碳水化合物，以支持 物种的生长和生存。了解微生物与木质纤维素附着和降解的机制对于开发将植物生物质转化为燃料和化学品的有效方法非常重要。 物种在高温下利用木质纤维素中的碳水化合物生长，因此具有生物技术意义。新型纤维素结合蛋白，称为 tāpirins，参与了 物种与微晶纤维素相互作用的方式，本文还提供了有关该属中这些蛋白质多样性的更多信息，包括结合亲和力和三维结构比较。
