Anderson K E, Waite J H
College of Marine Studies, Newark, Delaware 19716, USA.
Biol Bull. 1998 Apr;194(2):150-60. doi: 10.2307/1543045.
The zebra mussel is a nonindigenous invader of North American lakes and rivers and one of the few freshwater bivalve molluscs having a byssus--a sclerotized organ used by the mussel for opportunistic attachment to hard surfaces. We have sequenced a foot-specific cDNA whose composite protein sequence was deduced from a series of overlapping but occasionally nonidentical cDNA fragments. The overall deduced sequence matches tryptic peptides from a major byssal precursor protein--Dreissena polymorpha foot protein 1 (Dpfp1). The calculated mass of Dpfp1 is 49 kDa; but this is known to be extensively hydroxylated and O-glycosylated during maturation. Purified native Dpfp1 analyzed using matrix-assisted laser-desorption ionization mass spectrometry with time-of-flight indicates that the protein occurs as at least two size variants with masses of 48.6 and 54.5 kDa. In all probability, the sequence variants reported in this study are related to the larger mass variant. Dpfp1 has a block copolymer-like structure defined by two consensus motifs that are sharply segregated into domains. The N-terminal side of Dpfp1 has 22 tandem repeats of a heptapeptide consensus (P-[V/E]-Y-P-[T/S/delta]-[K/Q]-X); the C-terminal side has 16 repeats of a tridecapeptide motif (K-P-G-P-Y-D-Y-D-G-P-Y-D-K). Both consensus repeats are unique, with some limited homology to other proteins functioning in tension: marine mussel adhesives, plant extensins, titin, and trematode eggshell precursors.
斑马贻贝是北美湖泊和河流中的一种非本土入侵物种，也是少数具有足丝的淡水双壳贝类之一——足丝是一种硬化器官，贻贝利用它随机附着在坚硬表面上。我们对一个足部特异性cDNA进行了测序，其复合蛋白质序列是从一系列重叠但偶尔不相同的cDNA片段推导出来的。总体推导序列与一种主要足丝前体蛋白——多形饰贝足部蛋白1（Dpfp1）的胰蛋白酶肽段相匹配。Dpfp1的计算质量为49 kDa；但已知在成熟过程中它会大量羟基化和O-糖基化。使用基质辅助激光解吸电离飞行时间质谱分析纯化的天然Dpfp1表明，该蛋白至少以两种大小变体的形式存在，质量分别为48.6 kDa和54.5 kDa。很有可能，本研究中报道的序列变体与较大质量的变体有关。Dpfp1具有一种类似嵌段共聚物的结构，由两个共有基序定义，这两个共有基序明显分隔成不同结构域。Dpfp1的N端有22个七肽共有序列（P-[V/E]-Y-P-[T/S/δ]-[K/Q]-X）的串联重复；C端有16个十三肽基序（K-P-G-P-Y-D-Y-D-G-P-Y-D-K）的重复。这两个共有重复序列都是独特的，与其他在张力中起作用的蛋白质有一些有限的同源性：海洋贻贝黏附蛋白、植物伸展蛋白、肌联蛋白和吸虫卵壳前体。
