The 2.1A crystal structure of copGFP, a representative member of the copepod clade within the green fluorescent protein superfamily

The green fluorescent protein (avGFP), its variants, and the closely related GFP-like proteins are characterized structurally by a cyclic tri-peptide chromophore located centrally within a conserved beta-can fold. Traditionally, these GFP family members have been isolated from the Cnidaria although recently, distantly related GFP-like proteins from the Bilateria, a sister group of the Cnidaria have been described, although no representative structure from this phylum has been reported to date. We have determined to 2.1A resolution the crystal structure of copGFP, a representative GFP-like protein from a copepod, a member of the Bilateria. The structure of copGFP revealed that, despite sharing only 19% sequence identity with GFP, the tri-peptide chromophore (Gly57-Tyr58-Gly59) of copGFP adopted a cis coplanar conformation within the conserved beta-can fold. However, the immediate environment surrounding the chromophore of copGFP was markedly atypical when compared to other members of the GFP-superfamily, with a large network of bulky residues observed to surround the chromophore. Arg87 and Glu222 (GFP numbering 96 and 222), the only two residues conserved between copGFP, GFP and GFP-like proteins are involved in autocatalytic genesis of the chromophore. Accordingly, the copGFP structure provides an alternative platform for the development of a new suite of fluorescent protein tools. Moreover, the structure suggests that the autocatalytic genesis of the chromophore is remarkably tolerant to a high degree of sequence and structural variation within the beta-can fold of the GFP superfamily.     

copGFP和PuroR双标记基因慢病毒融合表达载体的构建及应用*

目的: 构建具有绿色荧光蛋白(copGFP)和嘌呤霉素抗性基因(PuroR)融合表达双筛选标记的慢病毒过表达载体,检测其嘌呤霉素抗性和绿色荧光蛋白表达的特性。方法: 从pCDH-CMV-MCS-copGFP载体中扩增copGFP编码区DNA序列,从pLKO.1载体中扩增Puro^R编码区DNA序列,运用重组PCR方法,扩增copGFP与Puro^R基因融合编码序列并克隆至经BamH Ⅰ+Sal Ⅰ双酶切的pCDH-CMV-MCS-copGFP载体片段中,构建含copGFP和Puro^R融合表达双筛选标记的慢病毒过表达载体;载体的融合标签序列进行测序确证;将该载体用辅助包装质粒PLP1、PLP2、VSVG在293T细胞中包装成慢病毒后感染肝癌细胞MHCC97H,检测感染细胞对嘌呤霉素的抵抗作用以及绿色荧光蛋白的表达情况;为验证该载体表达外源目的基因的有效性,将Sp1编码区DNA序列插入该载体中包装成慢病毒,用对照及表达Sp1的慢病毒感染肝癌细胞MHCC97H,感染细胞经1 mg/ml嘌呤霉素筛选7 d后获得稳定感染细胞株,提取稳定感染细胞的总RNA及总蛋白,分别运用RT-qPCR和Western blot方法检测Sp1在对照及表达Sp1的慢病毒感染的肝癌MHCC97H细胞中的mRNA和蛋白表达水平的差异。结果: 成功构建含copGFP和Puro^R融合表达双筛选标记的慢病毒过表达载体;该载体与辅助质粒包装出的慢病毒感染肝癌细胞后,感染细胞同时具有嘌呤霉素抗性和表达绿色荧光蛋白特性;将Sp1编码序列插入该载体,包装慢病毒并肝癌细胞,Sp1 的mRNA水平对照细胞相比分别升高3.3倍,蛋白水平升高2.2倍(P＜0.01)。 结论: 成功构建含copGFP和Puro^R融合表达双筛选标记的慢病毒过表达载体,该载体编码的融合双标记基因具有嘌呤霉素抗性和绿色荧光蛋白表达的特性,可高水平表达长片段的目的基因。     

Optimization of a genome-wide disordered lentivector-based short hairpin RNA library

To obtain a whole genome library that suppresses the total diversity of human mRNAs, lentiviral vector constructs and a short hairpin RNA (shRNA) expression cassette were optimized. The optimization of the vector increased the virus titer in preparations by 15–20 times. A simple shRNA structure with a 21-bp stem proved to be the most effective. Lentivector-based shRNA expression constructs were obtained by using puro ^R, copGFP, or H-2K ^k as a selectable marker. The efficiency of the optimized library was demonstrated when screening for shRNAs reactivating the tumor suppressor p53 in HeLa cells. Cells carried a reporter construct ensuring p53-responsive synthesis of a fluorescent protein, which allowed selection of cells with reactivated p53 by flow cytometry.