Site-directed mutagenesis of arginine-89 supports the role of its guanidino side-chain in substrate binding by Cephalosporium acremonium isopenicillin N synthase

Isopenicillin N synthase (IPNS) catalyses a key step in the penicillin and cephalosporin biosynthetic pathway which involves the oxidative cyclisation of the acyclic peptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) to isopenicillin N. Based on crystallographic evidence from the Aspergillus nidulans IPNS crystal structure complexed with the substrate ACV (Roach et al. (1997) Nature 387, 827-830), we were able to provide mutational evidence for the critical involvement of the conserved R-X-S motif in ACV binding in IPNS. The crystal structure further implicated arginine-87 in the binding of the aminoadipyl portion of ACV. Thus, in this study, the site-directed mutagenesis of the corresponding arginine-89 in Cephalosporium acremonium IPNS (cIPNS) was performed to ascertain its role in cIPNS. Alteration of arginine-89 to five amino acids from different amino acid groups, namely lysine, serine, alanine, aspartate and leucine, was performed and no activity was detected in all the mutants obtained when enzyme bioassays were performed. Furthermore, the solubility of the mutants was considerably lower than the wild-type cIPNS after expression at 37 degrees C, but could be recovered when the expression temperature was lowered to 25 degrees C. This suggests that arginine-89 could be critical for the activity of cIPNS due to its involvement in ACV binding and the solubility of wild-type enzyme.     

面向国家公园管理目标的综合灾害风险管理:一个概念模型

减小阻碍国家公园管理目标实现的灾害风险，实现管理有效性，是保证国家公园体制建设建立的重要途径。研究提出，面向国家公园多元管理目标，保障社会-生态系统稳定性和恢复力，国家公园灾害风险管理具有综合性。这种综合性体现在国家公园内致灾因子与承灾体的多样性、相对性与转化性，需要集成分别侧重社会与生态系统的传统自然灾害风险管理与生态风险管理，让灾害风险管理贯穿国家公园具体管理。为实现集成应对这种综合性，研究首先总结国内外多类型自然保护地灾害风险管理特点与经验，辨析国家公园灾害风险管理在国家公园管理职责和管理规划中的定位，从3个方面提出对我国国家公园灾害风险管理的启示：1）需要与国家公园宏观管理目标紧密相连；2）以维持社会-生态系统理想状态为目标；3）要具有管理空间、时间与运行的整体性。在此基础上提出一个面向国家公园管理目标的综合灾害风险管理框架，其主要特点是：1）具有"层级式"管理目标；2）以社会-生态系统服务为评价终点开展以理想状态为目标的风险管理；3）联结研究与管理、协调科学与价值观进行适应性管理。     

Maternal Urinary Iodine Concentration and Pregnancy Outcomes: Tehran Thyroid and Pregnancy Study

Biological Trace Element Research - Long-term use of hair dyes has potential effects on metal content in hair. However, little research dissects the specific distribution and composition variations...