Perlick A M, Frühling M, Schröder G, Frosch S C, Pühler A
Universität Bielefeld, Lehrstuhl für Genetik, Germany.
Plant Physiol. 1996 Jan;110(1):147-54. doi: 10.1104/pp.110.1.147.
Nodulin gene transcripts isolated from a broad bean (Vicia faba L.) root nodule cDNA library and designated VfNOD32 are detectable in the nitrogen-fixing zone III of nodules and in much smaller amounts in flowers. In nodules, these transcripts are detectable for the first time 7 d after inoculation, at least 1 d before leghemoglobin gene transcription starts. Two putative full-length cDNAs representing different transcript sequences of 92.5% identity were sequenced. The corresponding broad bean genes were termed VfNOD32-A1 and VfNOD32-A2, and the encoded proteins were termed Nvf32-A1 and Nvf32-A2. The derived amino acid sequences of the Nvf32 proteins are highly homologous to the Vicia narbonensis (alpha/beta)8-barrel seed protein narbonin. Considering this homology, Nvf32 is assumed to have a similar structure consisting of beta-sheets forming a central barrel surrounded by alpha-helices. The two Nvf32 sequences also contain two conserved amino acid motifs that are characteristic of class-III chitinases. Several amino acids demonstrated to be essential for chitinase activity are conserved in both regions, whereas one essential glutamic acid was changed to glycine in the Nvf32-A1 isoform but not in the Nvf32-A2 isoform.
从蚕豆（Vicia faba L.）根瘤cDNA文库中分离得到的、命名为VfNOD32的根瘤菌素基因转录本，在根瘤的固氮Ⅲ区可检测到，在花中也有少量表达。在根瘤中，接种后7天首次检测到这些转录本，比豆血红蛋白基因转录开始至少早1天。对两个代表不同转录本序列、同一性为92.5%的推定全长cDNA进行了测序。相应的蚕豆基因被命名为VfNOD32-A1和VfNOD32-A2，编码的蛋白质被命名为Nvf32-A1和Nvf32-A2。Nvf32蛋白的推导氨基酸序列与窄叶野豌豆（α/β）8桶状种子蛋白narbonin高度同源。基于这种同源性，推测Nvf32具有类似的结构，由β-折叠形成一个中央桶状结构，周围环绕着α-螺旋。这两个Nvf32序列还包含两个Ⅲ类几丁质酶特有的保守氨基酸基序。在两个区域中，几个被证明对几丁质酶活性至关重要的氨基酸是保守的，而在Nvf32-A1同工型中，一个必需的谷氨酸被改变为甘氨酸，而在Nvf32-A2同工型中则没有。
