Faculty of Bioscience, Nagahama Institute of Bio-Science and Technology, 1266 Tamura-Cho, Nagahama, Shiga 526-0829, Japan.
Department of Biomolecular Science, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8577, Japan.
Proteins. 2018 Jun;86(6):644-653. doi: 10.1002/prot.25491. Epub 2018 Mar 23.
The nacreous layer of pearl oysters is one of the major biominerals of commercial and industrial interest. Jacalin-related lectins, including PPL3 isoforms, are known to regulate biomineralization of the Pteria penguin pearl shell, although the molecular mechanisms are largely unknown. The PPL3 crystal structures were determined partly by utilizing microgravity environments for 3 isoforms, namely, PPL3A, PPL3B, and PPL3C. The structures revealed a tail-to-tail dimer structure established by forming a unique inter-subunit disulfide bond at C-termini. The N-terminal residues were found in pyroglutamate form, and this was partly explained by the post-translational modification of PPL3 isoforms implied from the discrepancy between amino acid and gene sequences. The complex structures with trehalose and isomaltose indicated that the novel specificity originated from the unique α-helix of PPL3 isoforms. Docking simulations of PPL3B to various calcite crystal faces suggested the edge of a β-sheet and the carbohydrate-binding site rich in charged residues were the interface to the biomineral, and implied that the isoforms differed in calcite interactions.
珍珠贝的珍珠层是具有商业和工业价值的主要生物矿物之一。已知 Jacalin 相关凝集素（包括 PPL3 同工型）可调节珍珠贝的生物矿化，尽管其分子机制在很大程度上尚不清楚。利用微重力环境确定了 3 种同工型（PPL3A、PPL3B 和 PPL3C）的 PPL3 晶体结构。结构显示了由 C 末端形成独特的亚基间二硫键建立的尾对尾二聚体结构。在 N 端残基发现了焦谷氨酸形式，这部分可以通过 PPL3 同工型的翻译后修饰来解释，这与氨基酸和基因序列之间的差异有关。与海藻糖和异麦芽糖的复合物结构表明，新型特异性源于 PPL3 同工型独特的α-螺旋。对 PPL3B 与各种方解石晶体面的对接模拟表明，β-折叠的边缘和富含带电残基的碳水化合物结合位点是与生物矿物的界面，并暗示同工型在方解石相互作用中存在差异。
