Becker Pierre T, Lambert Aurélie, Lejeune Annabelle, Lanterbecq Déborah, Flammang Patrick
Université de Mons-UMONS, Laboratoire de Biologie des Organismes Marins et Biomimétisme, 23 Place du Parc, 7000 Mons, Belgium.
Biol Bull. 2012 Oct;223(2):217-25. doi: 10.1086/BBLv223n2p217.
The shelter of the tube-dwelling polychaete Sabellaria alveolata is composed of mineral particles assembled with spots of a proteinaceous cement. The adhesive proteins constituting the cement were identified on the basis of their sequence similarity with proteins of a phylogenetically related species, Phragmatopoma californica. Two positively charged proteins, Sa-1 and Sa-2, share common features: they both have a mass of 22 kDa; are rich in glycine, tyrosine and basic residues; and show repeated peptide motifs. The consensus repeat of Sa-1 is KGAYGAKGLGYGNKAGYGAYG (occurring 6-8 times), while Sa-2 displays the consensus heptapeptide VHKAAWG (5 times) and undecapeptide VHKAAGYGGYG (8 times). Two variants of a serine-rich protein, Sa-3A (22 kDa) and Sa-3B (21 kDa), were also identified. Their serine residues account for 75 mol% and are probably phosphorylated, meaning that Sa-3 is very acidic and negatively charged. Moreover, tyrosine residues of all adhesive proteins are presumably modified into DOPA. Although protein sequences are not well-conserved between S. alveolata and P. californica, their main characteristics (including amino acid composition, post-translational modifications, repeated patterns, isoelectric point, and mass) are shared by both species. This suggests that these features are more important for their function than the primary structure of the proteins. The mRNA abundance for each protein was estimated by quantitative real-time PCR, revealing relative expression levels of about 5, 11, 1.5, and 1 for Sa-1, -2, -3A, and -3B, respectively. These levels could be indicative of charge neutralization phenomena or could reflect their function (interface vs. bulk) in the cement.
管栖多毛纲动物沙蠋（Sabellaria alveolata）的栖管由矿物颗粒与蛋白质类黏合剂斑点组装而成。基于与系统发育相关物种加州苔藓虫（Phragmatopoma californica）蛋白质的序列相似性，鉴定出了构成黏合剂的黏附蛋白。两种带正电荷的蛋白质Sa - 1和Sa - 2具有共同特征：它们的质量均为22 kDa；富含甘氨酸、酪氨酸和碱性残基；并显示出重复的肽基序。Sa - 1的共有重复序列为KGAYGAKGLGYGNKAGYGAYG（出现6 - 8次），而Sa - 2则显示共有七肽VHKAAWG（5次）和十一肽VHKAAGYGGYG（8次）。还鉴定出了一种富含丝氨酸的蛋白质的两种变体，Sa - 3A（22 kDa）和Sa - 3B（21 kDa）。它们的丝氨酸残基占75 mol%，可能被磷酸化，这意味着Sa - 3非常酸性且带负电荷。此外，所有黏附蛋白的酪氨酸残基可能被修饰为多巴。尽管沙蠋和加州苔藓虫之间的蛋白质序列保守性不佳，但这两个物种共享它们的主要特征（包括氨基酸组成、翻译后修饰、重复模式、等电点和质量）。这表明这些特征对其功能而言比蛋白质的一级结构更重要。通过定量实时PCR估计了每种蛋白质的mRNA丰度，结果显示Sa - 1、- 2、- 3A和- 3B的相对表达水平分别约为5、11、1.5和1。这些水平可能表明电荷中和现象，或者可能反映它们在黏合剂中的功能（界面与本体）。
