Propeptide-Mediated Allosteric Regulation of Xylanase Xyl-1: An Integrated Experimental and Computational Analysis

Most GH11 family endo-β-1,4-xylanases contain a propeptide region linked to the N-terminal region. The mechanistic basis of this region harboring key regulation information for enzyme function, however, remains poorly understood. We reported an investigation on the allosteric regulation mechanism of the propeptide based on biochemical characterization, molecular dynamics simulations, and evolutionary analysis. We discovered that the mutant of truncated propeptide shows a remarkably increased thermal stability (melting temperature increased by 11.5 °C) and catalytic efficiency (1.7-fold k_cat/K_m value of wild type). Molecular dynamics simulations reveal that long-range fluctuations in the propeptide lead to a conformational perturbation in the catalytic pocket and the thumb region. The probability of sampling the active conformation during the glycosylation step is reduced (i.e., catalytic efficiency). In-depth sequence analysis indicates that the propeptide has a strong plasticity and degeneration trend, and propeptide truncation experiments of the homologous enzyme XynB validated the feasibility of the truncation strategy. This work reveals the role of GH11 family propeptides in functional regulation and provides a straightforward and practical method to increase the robustness of GH11 family xylanases.

[A clinical analysis of micafungin treatment of pulmonary invasive fungal infection in pediatric patients with acute leukemia or post hematopoietic stem cells transplantation]

Objective: To investigate the efficacy and safety of micafungin (MCF) for pulmonary invasive fungal disease (PIFD) in pediatric patients with acute leukemia or post hematopoietic stem cells transplantation. Method: Twenty-five neutropenic PIFD children with acute leukemia or post hematopoietic stem cells transplantation in Sun Yat-sen Memorial Hospital of Sun Yat-sen University were selected from January 2012 to June 2015, including 12 males and 13 females, age range 2-15 (average 6.2±2.0) years. There were 12 cases of acute leukemia (AL) after chemotherapy, 4 cases of acute leukemia (AL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and 9 cases of β-thalassemia major after allo-HSCT. All children received MCM for the treatment of PIFD, the dosage of MCM was 3-4 mg/ (kg·d) , once a day. The children received 2 to 6 courses of treatment, individually with a course of 7 days. 1, 3-β-D glucan assay (G test), galactomannan antigen test (GM test), high-resolution CT and the biochemical indexes for organ functions were closely monitored. Result: Twenty-five cases were diagnosed as PIFD, including 2 patients diagnosed as proven, 6 as probable and 17 as possible. Of the 25 cases, 1 was confirmed aspergillus by biopsy pathology and 1 was candida albicans by blood culture. The G and GM test with positive results was 5 and 2 respectively. Chest CT scans of the 25 cases had obvious lesions: air crescent sign and cavitation in 4 cases, diffuse ground glass change in 9 cases, double lung scattered patchy, small nodules and cord like high density shadow in 7 cases, unilateral or bilateral chest wall wedge-shaped consolidation edge in 5 cases and pleural effusion in 5 patients. The effective rate of MCF in treatment of PIFD was 68% (17/25), including 13 cases cured, 4 cases improved, 4 cases were improved clinically and in 4 cases the treatment was ineffective. Eight cases were effective in MCF monotherapy group (12 cases) and nine were effective in MCF combined therapy group(13 cases), respectively. Side-effects including allergies, gastrointestinal side effects, electrolyte disturbances, impairment of liver and kidney function, and myelosuppression were not found in those children treated with MCF. Conclusion: Micafungin is effective and safe in the treatment of pulmonary invasive fungal disease in pediatric patients with acute leukemia or post hematopoietic stem cell transplantation.