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Abstract：
The attainment of new function by a protein is achieved through convergent/divergent evolution. In present work, the sequence analysis of a 34kDa protein from Putranjiva roxburghii, earlier reported as a potent trypsin inhibitor, showed resemblance to some of the wound inducible and vegetative storage proteins. A detailed sequence analysis revealed that these proteins belong to PNP-UDP family. In case of P. roxburghii protein, an approximately 46 residue insert disrupts the PNP domain. Similar disruption of PNP domain is observed in related plant proteins. The characterization of recombinant full length and truncated (without 46 residue insert) forms of P. roxburghii PNP family protein (PRpnp) unraveled that trypsin inhibitory active site is located within the insert. The truncated form containing uninterrupted PNP domain showed strong PNP enzymatic activity where it hydrolyzed the N-glycosidic bond of inosine and guanosine. The full length protein, however, showed weak PNP enzyme activity which may be due to presence of the insert. These results indicate towards the neofunctionalization of PRpnp to a potent trypsin inhibitor through an insert containing inhibitory residue to cater to the needs of plant defense. The similar wound inducible and vegetative storage proteins may have also evolved due to evolutionary needs.
摘要：
蛋白质实现新功能是通过趋同/发散进化实现的。在目前的工作中,来自刺梨的34kDa蛋白的序列分析，早期报道是一种有效的胰蛋白酶抑制剂，显示出与某些伤口可诱导和营养储存蛋白的相似性。详细的序列分析表明这些蛋白质属于PNP-UDP家族。在刺梨蛋白的情况下，大约46个残基的插入片段破坏PNP结构域。在相关植物蛋白中观察到PNP结构域的类似破坏。重组全长和截短(无46个残基插入)形式的刺梨PNP家族蛋白(PRpnp)的表征揭示了胰蛋白酶抑制活性位点位于插入片段内。含有不间断PNP结构域的截短形式显示出强的PNP酶活性,其中它水解肌苷和鸟苷的N-糖苷键。全长蛋白质，然而,显示弱的PNP酶活性，这可能是由于插入物的存在。这些结果表明通过含有抑制残基的插入物将PRpnp新功能化为有效的胰蛋白酶抑制剂，以满足植物防御的需要。类似的伤口诱导型和营养储存蛋白也可能由于进化需要而进化。
