Knudson-Goerner Emily, Boraston Alisdair B
Biochemistry and Microbiology, University of Victoria, PO Box 1700 STN CSC, Victoria, BC V8W 2Y2, Canada.
Acta Crystallogr F Struct Biol Commun. 2025 Jul 1;81(Pt 7):281-286. doi: 10.1107/S2053230X2500425X. Epub 2025 May 27.
The genome of the marine bacterium Muricauda eckloniae sp. DK169 contains an extensive polysaccharide-utilization locus that targets fucoidan from brown algae. Within this locus is a gene that encodes a putative fucoidan-degrading glycoside hydrolase (locus tag AAY42_01205) assigned to glycoside hydrolase family 168, which we call MeGH168. We present the 2.0 Å resolution X-ray crystal structure of MeGH168, demonstrating a (β/α)-barrel fold. The eight loop regions joining each α-helix and β-strand surround the catalytic groove. A comparison with the structure of a GH168, Fun168A, in complex with a fragment of fucoidan (PDB entry 8ya7) revealed conservation of key residues in the catalytic site. However, structural variation in positive-subsite loop regions may recontour the active site to create differences in substrate specificity between the two GH168s. The present data provide additional structural insights into the GH168 family, particularly expanding on sequence and structure conservation (and the lack thereof) in relation to substrate interactions.
海洋细菌海带缪氏菌（Muricauda eckloniae）DK169的基因组包含一个广泛的多糖利用位点，该位点靶向褐藻中的岩藻依聚糖。在这个位点内有一个基因，编码一种假定的岩藻依聚糖降解糖苷水解酶（基因座标签AAY42_01205），属于糖苷水解酶家族168，我们将其称为MeGH168。我们展示了MeGH168分辨率为2.0 Å的X射线晶体结构，显示出一种（β/α）-桶状折叠。连接每个α-螺旋和β-链的八个环区域围绕着催化凹槽。与与岩藻依聚糖片段结合的GH168，即Fun168A的结构（蛋白质数据银行条目8ya7）进行比较，发现催化位点中的关键残基具有保守性。然而，正亚位点环区域的结构变化可能会重塑活性位点，从而导致两种GH168在底物特异性上产生差异。目前的数据为GH168家族提供了更多的结构见解，特别是在与底物相互作用相关的序列和结构保守性（以及缺乏保守性）方面进行了拓展。
