Waite J H, Rice-Ficht A C
Marine Biology/Biochemistry Program, College of Marine Studies, University of Delaware, Lewes 19958.
Mol Biochem Parasitol. 1992 Sep;54(2):143-51. doi: 10.1016/0166-6851(92)90107-u.
At least 3 structural protein precursors of the eggshell are synthesized and stockpiled in the extensive vitelline cells of the liver fluke Fasciola hepatica L. One of these, vitelline protein B, consists of a closely related family of proteins that owes its apparent electrophoretic heterogeneity to variations in the Tyr to DOPA conversion as well as to subtle variations in the primary sequence. The efficiency of the Tyr to DOPA conversion ranges from a maximum of about 90% to a minimum of 55% in the protein. Trypsin digestion in borate buffer at pH 8 was used to produce DOPA-peptides for sequencing. Notably, trypsin does not cleave Arg/Lys-DOPA sequences at borate concentrations greater than 0.15 M. Peptides with DOPA-containing sequences most frequently have flanking amino acids such as Lys, Ser, or Asp on the N-terminal side and Gly or Asp on the C-terminal side. All protein variants fall within a narrow molecular weight range (30-33 kDa), a pI range of 6.9 to 8.3, and the collective majority would appear to share a common N-terminal sequence up to residue 28. The results suggest some combination of the following: variations in post-translational hydroxylation, alternative post-transcriptional splicing and/or the existence of multiple gene copies of eggshell precursors. The latter have been shown to occur in the blood fluke Schistosoma mansoni [15].
肝片吸虫（Fasciola hepatica L.）卵壳的至少3种结构蛋白前体在肝脏广泛的卵黄细胞中合成并储存。其中一种，卵黄蛋白B，由一个密切相关的蛋白质家族组成，其明显的电泳异质性归因于酪氨酸向多巴转化的变化以及一级序列中的细微变化。在该蛋白质中，酪氨酸向多巴转化的效率范围从最高约90%到最低55%。在pH 8的硼酸盐缓冲液中用胰蛋白酶消化来产生用于测序的多巴肽。值得注意的是，在硼酸盐浓度大于0.15 M时，胰蛋白酶不会切割精氨酸/赖氨酸 - 多巴序列。含有多巴序列的肽在N端最常见的侧翼氨基酸有赖氨酸、丝氨酸或天冬氨酸，在C端有甘氨酸或天冬氨酸。所有蛋白质变体都在一个狭窄的分子量范围（30 - 33 kDa）、pI范围6.9至8.3内，并且大多数似乎在第28个残基之前共享一个共同的N端序列。结果提示以下几种情况的某种组合：翻译后羟基化的变化、转录后选择性剪接和/或卵壳前体多基因拷贝的存在。后者已在曼氏血吸虫（Schistosoma mansoni）中被证明存在[15]。
