Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Queensland University of Technology, Brisbane, Australia.
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia.
Int J Biol Macromol. 2021 Jan 1;166:1230-1237. doi: 10.1016/j.ijbiomac.2020.11.005. Epub 2020 Nov 4.
KL55, KL74, and KL85 capsular polysaccharide (CPS) biosynthesis loci in Acinetobacter baumannii BAL_204, BAL_309, and LUH5543 genomes, respectively, are related and each contains genes for l-Rhap and d-GlcpA synthesis. The CPSs were isolated and studied by sugar analysis, Smith degradation, and H and C NMR spectroscopy. The K55 and K74 CPSs are built up of branched octasaccharide repeats (K units) containing one residue each of d-GlcpA and d-GlcpNAc and six residues of l-Rhap. The K55 unit differs from the K74 unit in the linkage between D-GlcpA and an l-Rhap residue in the K unit (1 → 3 versus 1 → 2) and linkage between K units. However, most K units in the isolated K74 CPS were modified by β-elimination of a side-chain α-l-Rhap-(1 → 3)-α-l-Rhap disaccharide from position 4 of GlcA to give 4-deoxy-l-threo-hex-4-enuronic acid (1:~3 ratio of intact and modified units). The K85 CPS has a branched heptasaccharide K unit similar to the K74 unit but with one fewer α-l-Rhap residue in the side chain. In contrast to previous findings on A. baumannii CPSs, each K locus includes fewer glycosyltransferase (Gtr) genes than the number required to form all linkages in the K units. Hence, one Gtr appears to be multifunctional catalysing formation of two 1 → 2 and one 1 → 3 linkages between the l-Rha residues.
分别在鲍曼不动杆菌 BAL_204、BAL_309 和 LUH5543 基因组中发现 KL55、KL74 和 KL85 荚膜多糖（CPS）生物合成基因座，它们彼此相关，每个基因座都包含 l-Rhap 和 d-GlcpA 合成基因。通过糖分析、Smith 降解和 H 和 C NMR 光谱学对 CPS 进行了分离和研究。K55 和 K74 CPS 由含有一个 d-GlcpA 和 d-GlcpNAc 残基以及六个 l-Rhap 残基的分支八糖重复（K 单元）组成。K55 单元与 K74 单元在 K 单元中 D-GlcpA 与 l-Rhap 残基之间的连接（1→3 对 1→2）以及 K 单元之间的连接方式不同。然而，分离的 K74 CPS 中的大多数 K 单元通过从 GlcA 的 4 位侧链α-l-Rhap-（1→3）-α-l-Rhap 二糖的β消除进行修饰，得到 4-去氧-l-苏-己-4-烯酸（完整和修饰单元的 1：3 比例）。K85 CPS 具有与 K74 单元相似的分支七糖 K 单元，但在侧链中少一个 α-l-Rhap 残基。与之前关于鲍曼不动杆菌 CPS 的发现相反，每个 K 基因座包含的糖基转移酶（Gtr）基因少于形成 K 单元中所有键所需的数量。因此，一个 Gtr 似乎具有多功能性，能够催化 l-Rha 残基之间形成两个 1→2 和一个 1→3 键。
