Insight into the Highly Conserved and Differentiated Cofactor-Binding Sites of meso-Diaminopimelate Dehydrogenase StDAPDH.

meso-Diaminopimelate dehydrogenase ( meso-DAPDH) is a good candidate for one-step synthesis of d-amino acid from 2-keto acids. Our previous research revealed the classification of meso-DAPDH family and showed that type II meso-DAPDH, such as the meso-DAPDH from Symbiobacterium thermophilum (StDAPDH), could catalyze reductive amination. In this article, seven residues of StDAPDH, which are highly conserved in each subfamily but are different between two subfamilies, were targeted to explore the relationships between structure and function. Determination of kinetic parameters showed that the amino acid residues, including P69, K159, V68, S90, V14, and V156, played very important roles in the catalytic function of StDAPDH. Molecular dynamics simulation revealed that these point mutations reduced the productive conformations by the newly formed or eliminated interactions between the residues and ligands. These results strengthen our understanding of the catalytic mechanism and evolution of meso-DAPDH and can aid future endeavors in enzyme engineering.

Multi­parameter quantitative magnetic resonance imaging in the early assessment of radiation­induced parotid damage in patients with nasopharyngeal carcinoma following intensity­modulated radiotherapy.

The present study aimed to investigate the value of intravoxel incoherent motion imaging (IVIM) and three-dimensional pulsed continuous arterial spin labeling (ASL) in assessing dynamic changes of the parotid gland in patients with nasopharyngeal carcinoma (NPC) following radiotherapy (RT). A total of 18 patients with NPC who underwent intensity-modulated RT were enrolled in the present study. All patients underwent conventional magnetic resonance imaging, plus IVIM and ASL imaging of the bilateral parotid glands within 2 weeks prior to RT, and 1 week (1W) and 3 months (3M) following RT. Pure diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (F) and blood flow (BF) were analyzed. D and BF values were significantly increased from pre-RT to 1W post-RT [change rate: Median (IQR), ΔD1W%: 39.28% (38.23%) and ΔBF1W%: 60.84% (54.88%)] and continued to increase from 1W post-RT to 3M post-RT [55.44% (40.56%) and ΔBF%: 120.39% (128.74%)]. In addition, the F value was significantly increased from pre-RT to 1W post-RT, [change rate: Median (IQR), ΔF1W%: 28.13% (44.66%)], and this decreased significantly from 1W post-RT to 3M post-RT. However, no significant differences were observed between pre-RT and 3M post-RT. Results of the present study also demonstrated that the D* value was significantly decreased from pre-RT to 1W post-RT and 3M post-RT [change rate: Median (IQR), ΔD*1w%: -41.86% (51.71%) and ΔD*3M: -29.11% (42.67%)]. No significant difference was observed between the different time intervals post-RT. There was a significant positive correlation between percentage change in ΔBF1W and radiation dose (ρ=0.548, P=0.001). Thus, IVIM-diffusion-weighted imaging and ASL may aid in the detection and prediction of radiation-induced parotid damage in the early stages following RT. They may contribute to further understanding the potential association between damage to the parotid glands and patient-/treatment-related variables, through the assessment of individual microcapillary perfusion and tissue diffusivity.

Combination of Quantitative Susceptibility Mapping and Diffusion Kurtosis Imaging Provides Potential Biomarkers for Early-Stage Parkinson's Disease.

Purpose: This study aimed to detect changes in iron deposition and neural microstructure in the substantia nigra (SN), red nucleus (RN), and basal ganglia of Parkinson's disease (PD) patients at different stages using quantitative susceptibility mapping and diffusion kurtosis imaging to identify potential indicators of early-stage PD. Methods: We enrolled 20 early-stage and 15 late-stage PD patients, as well as 20 age- and sex-matched controls. All participants underwent quantitative susceptibility mapping and diffusion kurtosis imaging to determine magnetic susceptibility (MS), fractional anisotropy (FA), mean diffusivity (MD), and mean kurtosis (MK) in several brain regions. Results: Compared with the control group, MS and MK values in the SN were significantly increased in the early- and late-stage PD group, whereas MS values in the red nucleus (RN), globus pallidus (GP), and caudate nucleus (CN), FA value in the CN and GP, and MK value in the CN and putamen (PU) were significantly increased in the late-stage PD group. There were positive correlations between MS and MK values in the CN and MS and FA values in the GP. Furthermore, the combination of MS and MK values in the SN provided high accuracy for distinguishing early-stage PD patients from controls. Conclusions: This study identified MS and MK in the SN as potential indicators of early-stage PD.

Essential role of amino acid position 71 in substrate preference by meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum IAM14863.

meso--Diaminopimelate dehydrogenase (meso-DAPDH) catalyzes the reversible oxidative deamination of the d-configuration of meso-2,6-diaminopimelate (meso-DAP) and is thought to have substrate specificity toward meso-DAP. The discovery of the meso-DAPDH from Symbiobacterium thermophilum IAM14863 (StDAPDH) revealed meso-DAPDH members with broad substrate specificity. In order to elucidate the substrate-preference mechanism of StDAPDH, it is necessary to identify the key residues related to this mechanism. Our previous work suggested that the non-active-site R71 of StDAPDH was related to substrate preference. Here, we report the key roles of the non-active site on the catalysis of StDAPDH. In order to explore the mechanism through which non-active-site R71 only affected the amination activity of StDAPDH, we performed molecular dynamic simulations and investigated the functional role of R71 in the type II meso-DAPDH StDAPDH. Site-directed mutagenesis with the allelic site A69 of CgDAPDH as a target proved that when replaced by Arg at position 71 of StDAPDH, the CgA69R mutant showed higher catalytic efficiencies toward a series of 2-keto acids, ranging from 1.2- to 1.5-fold. These findings provide some guidelines for improving our understanding of the broad substrate specificity of StDAPDH.