Marshall J, Holberton D V
Department of Life Science, Nottingham University, U.K..
J Cell Sci. 1995 Jul;108 ( Pt 7):2683-92. doi: 10.1242/jcs.108.7.2683.
Previously described extended proteins from the cytoskeleton of Giardia lamblia (beta-giardin, median body protein) have been found to be segmented coiled coils with regular structural repeat patterns in their amino acid sequences. Screening a lambda ZAPII library derived from Giardia genomic DNA with an antibody directed against a 34 x 10(3) M(r) giardin isoform selected a gene encoding a much larger polypeptide chain (HPSR2), the sequence of which was determined by chromosome walking the open reading frame. The complete gene has been cloned and expressed as a recombinant protein of 183 x 10(3) M(r). The predicted amino acid sequence of the protein has identifiable features suggesting that it might be a motor protein with an amino-terminal hydrolytic domain attached to a long coiled coil stalk. The presumed head domain is 211 residues and contains a P-loop sequence conserved in purine nucleotide-binding proteins. The remaining 1409 amino acids mainly make up a region of heptad repeats such as in myosin or the kinesin stalk, ending in a small (67 amino acids) carboxy-terminal domain. Fourier analysis of the predicted stalk shows the presence of a strong physical repeat created by regular heptad phase changes dividing the coil into segments of 25 residues. This structure most closely resembles the smaller microtubule-associated median body protein which has segments of 24 residues.
先前描述的来自贾第虫（蓝氏贾第鞭毛虫）细胞骨架的延伸蛋白（β-贾第虫素、中体蛋白）已被发现是分段的卷曲螺旋，其氨基酸序列具有规则的结构重复模式。用针对一种34×10³ M(r)贾第虫素同工型的抗体筛选源自贾第虫基因组DNA的λZAPII文库，选择了一个编码大得多的多肽链（HPSR2）的基因，其序列通过对开放阅读框进行染色体步移来确定。完整基因已被克隆并表达为一种183×10³ M(r)的重组蛋白。该蛋白的预测氨基酸序列具有可识别的特征，表明它可能是一种马达蛋白，其氨基末端水解结构域连接到一个长的卷曲螺旋柄上。推测的头部结构域有211个残基，包含在嘌呤核苷酸结合蛋白中保守的P环序列。其余1409个氨基酸主要构成一个七肽重复区域，如在肌球蛋白或驱动蛋白柄中，末端是一个小的（67个氨基酸）羧基末端结构域。对预测柄的傅里叶分析表明存在由规则的七肽相位变化产生的强烈物理重复，将卷曲螺旋分成25个残基的片段。这种结构与较小的微管相关中体蛋白最相似，后者有24个残基的片段。
