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MpaG' is an S‐adenosyl‐L‐methionine (SAM)‐dependent methyltransferase involved in the compartmentalized biosynthesis of mycophenolic acid (MPA), a first‐line immunosuppressive drug for organ transplantations and autoimmune diseases. MpaG' catalyzes the 5‐O‐methylation of three precursors in MPA biosynthesis including demethylmycophenolic acid (DMMPA), 4‐farnesyl‐3,5‐dihydroxy‐6‐methylphthalide (FDHMP), and an intermediate containing three fewer carbon atoms compared to FDHMP (FDHMP‐3C) with different catalytic efficiencies. Here, we report the crystal structures of S‐adenosyl‐L‐homocysteine (SAH)/DMMPA‐bound MpaG', SAH/FDHMP‐3C‐bound MpaG', and SAH/FDHMP‐bound MpaG' to understand the catalytic mechanism of MpaG' and structural basis for its substrate flexibility. Structural and biochemical analyses reveal that MpaG' utilizes the catalytic dyad H306‐E362 to deprotonate the C5 hydroxyl group of the substrates for the following methylation. The three substrates with differently modified farnesyl moieties are well accommodated in a large semi‐open substrate binding pocket with the orientation of their phthalide moiety almost identical. Based on the structure‐directed mutagenesis, a single mutant MpaG'Q267A is engineered with significantly improved catalytic efficiency for all three substrates. This study expands the mechanistic understanding and the pocket engineering strategy for O‐methyltransferases involved in fungal natural product biosynthesis. Our research also highlights the potential of O‐methyltransferases to modify diverse substrates by protein design and engineering. [ABSTRACT FROM AUTHOR]

Histone methylation is associated with transcription regulation, but its role for glycoside hydrolase (GH) biosynthesis is still poorly understood. We identified the histone H3 lysine 79 (H3K79)-specific methyltransferase Po Dot1 in Penicillium oxalicum. Po Dot1 affects conidiation by regulating the transcription of key regulators (BrlA, FlbC, and StuA) of asexual development and is required in normal hyphae septum and branch formation by regulating the transcription of five septin-encoding genes, namely, aspA , aspB , aspC , aspD , and aspE. Tandem affinity purification/mass spectrometry showed that Po Dot1 has no direct interaction with transcription machinery, but it affects the expressions of extracellular GH genes extensively. The expression of genes (amy15A , amy13A , cel7A/cbh1 , cel61A , chi18A , cel3A/bgl1 , xyn10A , cel7B/eg1 , cel5B/eg2 , and cel6A/cbh2) that encode the top 10 GHs was remarkably downregulated by Podot1 deletion (Δ Podot1). Consistent with the decrease in gene transcription level, the activities of amylases and cellulases were significantly decreased in Δ Podot1 mutants in agar (solid) and fermentation (liquid) media. The repression of GH gene expressions caused by Po Dot1 deletion was not mediated by key transcription factors, such as AmyR, ClrB, CreA, and XlnR, but was accompanied by defects in global demethylated H3K79 (H3K79me2) and trimethylated H3K79 (H3K79me3). The impairment of H3K79me2 on specific GH gene loci was observed due to Po Dot1 deletion. The results implies that defects of H3K79 methylation is the key reason of the downregulated transcription level of GH-encoding genes and reveals the indispensable role of PoDot1 in extracellular GH biosynthesis. [ABSTRACT FROM AUTHOR]

MpaG' is an S-adenosyl-L-methionine (SAM)-dependent methyltransferase involved in the compartmentalized biosynthesis of mycophenolic acid (MPA), a first-line immunosuppressive drug for organ transplantations and autoimmune diseases. MpaG' catalyzes the 5-O-methylation of three precursors in MPA biosynthesis including demethylmycophenolic acid (DMMPA), 4-farnesyl-3,5-dihydroxy-6-methylphthalide (FDHMP), and an intermediate containing three fewer carbon atoms compared to FDHMP (FDHMP-3C) with different catalytic efficiencies. Here, we report the crystal structures of S-adenosyl-L-homocysteine (SAH)/DMMPA-bound MpaG', SAH/FDHMP-3C-bound MpaG', and SAH/FDHMP-bound MpaG' to understand the catalytic mechanism of MpaG' and structural basis for its substrate flexibility. Structural and biochemical analyses reveal that MpaG' utilizes the catalytic dyad H306-E362 to deprotonate the C5 hydroxyl group of the substrates for the following methylation. The three substrates with differently modified farnesyl moieties are well accommodated in a large semi-open substrate binding pocket with the orientation of their phthalide moiety almost identical. Based on the structure-directed mutagenesis, a single mutant MpaG' Q267A is engineered with significantly improved catalytic efficiency for all three substrates. This study expands the mechanistic understanding and the pocket engineering strategy for O-methyltransferases involved in fungal natural product biosynthesis. Our research also highlights the potential of O-methyltransferases to modify diverse substrates by protein design and engineering., (© 2024 The Protein Society.)

This study reports the simplified carbapenem inactivation method (sCIM) to detect carbapenemase-producing gram-negative bacilli in a simple and accurate manner. This method is based on the modified carbapenem inactivation method (mCIM) with the improvement of experimental procedures. Instead of incubating the antibiotic disk in the organism culture media, the organism to be tested was smeared directly onto the antibiotic disk in the sCIM. For evaluating the sensitivity and specificity of the method, a total of 196 Enterobacteriaceae , 73 Acinetobacter baumannii , and 158 Pseudomonas aeruginosa isolates were collected. Polymerase chain reaction (PCR) was used to detect the carbapenemase genes. Phenotypic evaluations were performed using both the sCIM and the mCIM. PCR results showed that, of the 196 Enterobacteriaceae strains, 147 expressed the carbapenemase genes bla KPC-2 (58.5%), bla IMP-4 (21.8%), bla IMP-2 (2.0%), bla VIM-1 (6.1%), bla NDM-1 (10.2%), and bla OXA-48 (1.4%). sCIM results had high concordance with PCR results (99.5%) and mCIM results (100%) with the exception of one Klebsiella pneumoniae strain, which had an minimal inhibitory concentration (MIC) for imipenem of 0.25 mg/L. PCR demonstrated that 53 of the 73 A. baumannii isolates expressed the carbapenemase genes bla OXA-23 (98.1%) and bla VIM-2 (1.8%). sCIM and PCR results corresponded but all A. baumannii isolates were carbapenemase negative by the mCIM. PCR demonstrated that 25 of the 158 P. aeruginosa isolates expressed carbapenemase genes bla VIM-1 (52%) , bla VIM-2 (8%) , bla VIM-4 (36%), and bla IMP-4 (4%). sCIM results had high concordance with PCR results (100%) and the mCIM results (99.4%) with the exception of one P. aeruginosa isolate that expressed the bla VIM-4 gene. The sCIM offers specificity and sensitivity comparable to PCR but has the advantage of being more user-friendly. This method is suitable for routine use in most clinical microbiology laboratories for the detection of carbapenemase-producing gram-negative bacilli.

Objectives. To study the correlation between the methylation of protein kinase C epsilon zeta (PRKCZ) gene promoters and type 2 diabetes mellitus (T2DM). Methods. The case-control method was implemented in 272 unrelated to one another cases in Shiyan People's Hospital. Of those, 152 were diagnosed as T2DM cases, and the other 120 cases were healthy individuals visiting the hospital for a physical examination. The subjects were first divided into two groups: the T2DM group and the normal control (NC) group. Next, methylated DNA immunoprecipitation chip (MeDIP-chip) was used for detection. Bisulfite sequencing PCR (BSP) and gene sequencing were then performed to detect and analyze the correlation between PRKCZ gene promoter methylation and T2DM. Finally, Western blotting was applied to determine the serum level of PRKCZ. The data were then analyzed with the statistics analyzing software SPSS 17.0. Results. In contrast with cases in NC, T2DM patients showed a high level of methylation, with 7 of 9 CpG sites were shown to be methylated, whereas, in the control group, only one CpG site was found to be methylated. The methylated CpG sites for the two groups showed marked differences (P < 0.01). Additionally, the level of PRKCZ was decreased in T2DM subjects, and the difference between the two groups was statistically significant (P < 0.05). Discussion. This study suggests that the PRKCZ gene is the hypermethylated gene of T2DM and the hypermethylation PRKCZ gene may be involved in the pathogenesis of T2DM.