RESUMO
Escherichia coli cysteine desulfurase (CD), IscS, modifies basal metabolism by transferring sulphur (S) from L-cysteine to numerous cellular pathways, whereas NFS1, a human CD, is active only in the formation of the [Acp]2:[ISD11]2:[NFS1]2 complex. Despite the accumulation of red-coloured IscS in E. coli cells as a result of the deficiency of accessible iron, as revealed in our previous studies, the mechanism of the potential enzymatic reaction remains unclear. In this study, the N-terminus of IscS was fused with the C-terminus of NFS1, which was reported to be almost fully active as IscS and exhibits a pyridoxal 5'-phosphate (PLP) absorption peak at 395 nm. Moreover, SUMO-EH-IscS exhibited significant growth recovery and NADH-dehydrogenase I activity in the iscS mutant cells. Furthermore, through in vitro and in vivo experiments combined with high-performance liquid chromatography and ultra-performance liquid chromatography-tandem mass spectrometry, it was shown that the new absorption peaks of the IscS H104Q, IscS Q183E, IscS K206A, and IscS K206A&C328S variants at 340 and 350 nm may correspond to the enzyme reaction intermediates, Cys-ketimine and Cys-aldimine, respectively. However, after mutation of the conserved active-site residues, additional absorption peaks at 420 and 430 nm were associated with PLP migration in the active-site pocket. Additionally, the corresponding absorption peaks of Cys-quinonoid, Ala-ketimine, and Ala-aldimine intermediates in IscS were 510, 325, and 345 nm, respectively, as determined by site-directed mutagenesis and substrate/product-binding analyses during the CD reaction process. Notably, red IscS formed in vitro by incubating IscS variants (Q183E and K206A) with excess L-alanine and sulphide under aerobic conditions produced an absorption peak similar to the wild-type IscS, at 510 nm. Interestingly, site-directed mutation of IscS with hydrogen bonds to PLP at Asp180 and Gln183 resulted in a loss of enzymatic activity followed by an absorption peak consistent with NFS1 (420 nm). Furthermore, mutations at Asp180 or Lys206 inhibited the reaction of IscS in vitro with L-cysteine (substrate) and L-alanine (product). These results suggest that the conserved active site residues (His104, Asp180, and Gln183) and their hydrogen bond with PLP in the N-terminus of IscS play a key role in determining whether the L-cysteine substrate can enter the active-site pocket and regulate the enzymatic reaction process. Therefore, our findings provide a framework for evaluating the roles of conserved active-site residues, motifs, and domains in CDs.
RESUMO
As companies are transforming their branding, marketing, operations, and research and development (R&D) by running online communities to build their core competitive advantages in the digital era, the silent majority is still the norm in the online community and has become the focus of online community operations. Thus, it has become the core issue that why silent behavior of online community members occurs and its impact on operation performance of the online community. According to the traditional theory of organizational behavior, this study focuses on the theoretical model of the relationship between proactive personality, silent behavior of online community members (acquiescent, defensive, and prosocial silence), and operation performance of the online community, and further analyzes the impact of community identification on these relationships. Eight hundred online community members in China participated in this study. The results indicate that: (1) proactive personality has a significant negative impact on acquiescent silent and defensive silent behavior of the online community members, and a significant positive impact on prosocial silent behavior of the online community members; (2) The acquiescent silence and defensive silence have a significant negative impact on online community operation performance, whereas prosocial silence has a significant positive impact on community operation performance; (3) The acquiescent silence and defensive silence have a significant mediating effect on the relationship between proactive personality and community operation performance; (4) Online community identification has a moderating effect on the relationship between silent behavior and online community operation performance. The study proposes the mechanisms and double-edged sword effects of the silent behavior of online community members from the perspective of personality traits. On the one hand, it generalizes the research of traditional organizational silent behavior theory to the context of the online community. On the other hand, it provides reference and inspiration for the theoretical research and practical management of silent behavior of online community members.
RESUMO
OBJECTIVE: To study the clinicopathologic features and biologic behavior of pediatric immature teratoma. METHODS: The clinical data, pathologic features, immunohistochemical findings (for cyclin D1, P27 and Ki-67) and follow-up information of 39 cases of pediatric immature teratoma were analyzed. RESULTS: Amongst the 39 cases studied, 12 arose in the sacrococcygeal region, 12 in testis, 5 in retroperitoneum, 4 in ovary, 4 in abdomen and 2 in mediastinum. Histologically, 16 cases were of grade 1, 8 cases of grade 2 and 15 cases of grade 3. Seven of the cases contained foci of yolk sac tumor. Immature neuroepithelial features used in histologic grading included the presence of primitive neural tubules, immature rosettes, undifferentiated neuroblastoma cells and primitive neuroectodermal structures. Immunohistochemical study showed that cyclin D1 was positive in 3 cases of grade 1 tumors, 4 cases of grade 2 tumors and 9 cases of grade 3 tumors. The positivity rates for p27 were 8, 3 and 6 cases respectively, while those for Ki-67 were 3, 4 and 13 cases respectively. Follow-up data were available in 30 cases. Three of them, including 2 cases with histologic grade 3 (with or without yolk sac tumor component), recurred after operation. CONCLUSIONS: The expression of cyclin D1 and Ki-67 is a useful adjunct in histologic grading. On the other hand, p27 overexpression shows little correlation with tumor grade. The prognosis of immature teratoma in children is different from that in adults. Sacrococcygeal immature teratoma occurring in patients younger than 1 year old and with low histologic grade do not require postoperative chemotherapy if the tumor is completely excised. Similarly, for testicular immature teratoma occurring in patients below 1 year of age, regardless of tumor grading, need no adjunctive therapy. On the other hand, ovarian immature teratoma with high histologic grade requires postoperative chemotherapy, regardless of age of the patients. The presence of microscopic foci of yolk sac tumor is a useful predictor of recurrence in pediatric immature teratoma.
