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采用同源克隆从大珠母贝外套膜中扩增到2种编码N66类似蛋白的基因,分别命名为N36和N45。N36的开放阅读框为987 bp,编码329个氨基酸,推测分子量为35.7ku。N45的开放阅读框为1 164 bp,编码387个氨基酸,推测分子量为44.6 ku。二者都富含甘氨酸、天冬酰胺和天冬氨酸。N36蛋白不含信号肽,N45蛋白在N-端有一段22个氨基酸的信号肽。N36蛋白和N45蛋白分别有2个和1个糖基化位点,分别有13个和16个潜在的磷酸化位点,它们的二级结构都由α螺旋、β折叠和无规卷曲组成。系统进化分析显示N36和N45与N66进化关系最近,而与其他nacrein蛋白则距离较远。与合浦珠母贝的nacrein和大珠母贝的N66类似,N36和N45蛋白都包含2种功能结构域:1个α-碳酸酐酶结构域和1个Gly-Xaa-Asn(Xaa=Asp,Asn or Glu)重复结构域。推测N36和N45与珍珠层碳酸钙晶体的形成有关。
Homologous clones were used to amplify two kinds of genes encoding N66-like proteins from the mantle of mauve plexus and named N36 and N45, respectively. The N36 open reading frame was 987 bp, encoding 329 amino acids, suggesting a molecular weight of 35.7ku. The open reading frame of N45 was 1 164 bp, encoding 387 amino acids, suggesting a molecular weight of 44.6 ku. Both are rich in glycine, asparagine and aspartic acid. N36 protein does not contain signal peptide, N45 protein has a N-terminal 22 amino acid signal peptide. The N36 protein and the N45 protein have two and one glycosylation sites, respectively, with 13 and 16 potential phosphorylation sites, respectively, and their secondary structures consist of α-helix, β-sheet and random coil. Phylogenetic analysis showed that N36 and N45 had the closest evolutionary relationship with N66, but with other nacrein proteins. Similar to the nacrein of Pinctada tabaci and the N66 of Pinctada maxima, both N36 and N45 proteins contain two functional domains: one α-carbonic anhydrase domain and one Gly-Xaa-Asn (Xaa = Asp, Asn or Glu) repeat domain. It is speculated that N36 and N45 are related to the formation of nacreous calcium carbonate crystals.