External apical root resorption in African American orthodontic patients.

OBJECTIVE: External apical root resorption (EARR) is a side effect of orthodontic treatment that results in root shortening. However, this condition has yet to be evaluated in African Americans. The aim of this study was to determine the EARR prevalence within this ethnicity and investigate how patient and treatment-related factors contribute to root resorption. METHODS: The records of 336 African Americans treated at the University of Alabama at Birmingham School of Dentistry Department of Orthodontics were retrospectively analyzed with Dolphin Imaging software. Pre-treatment and post-treatment panoramic radiographs were used to measure EARR. Resorption was recorded when final roots were at least 2 mm shorter after orthodontic treatment. Additionally, moderate and severe EARR was reported when 20% and 50% or more of the root structure was lost for any of the four maxillary incisors, respectively. The Pearson chi-square test was used to evaluate the associations of individual patient and treatment-related factors with EARR. RESULTS: The prevalence of root resorption with 2 mm or greater of root structure loss was 51.8%. The prevalence of ≥ 20% EARR was 29.8%. Only one patient displayed severe resorption (0.3%). The associations between the patient-specific and treatment-specific variables and EARR were not statistically significant (P > .05). CONCLUSIONS: More than half of the African American patients exhibit at least 2 mm of root resorption with orthodontic treatment. However, in this ethnicity, patient-related factors such as age, gender, dental malocclusion, and skeletal classifications, as well as treatment-related factors do not indicate a significant correlation with the risk of developing EARR.

Genetic and other factors contributing to external apical root resorption in orthodontic patients.

OBJECTIVE: External apical root resorption (EARR) is a multifactorial disorder with adverse clinical outcomes in orthodontic practices often resulting in significant root shortening. This study examined the effect that specific single nucleotide polymorphisms (SNPs) have on the risk of developing EARR in orthodontic patients in X. We also evaluated how other selected patient- and treatment-related factors may contribute to root resorption in these patients. SETTING/SAMPLE: Patients included in this case-control study were treated at the University of Alabama at Birmingham School of Dentistry, Department of Orthodontics. METHODS: Panoramic radiographs were used to measure root resorption of the maxillary incisors. EARR was recorded when at least 20% of the root length had been lost with orthodontic treatment. Factors evaluated for association with EARR included ethnicity, sex, age, dental and skeletal classifications, ANB, U1-SN, overjet, treatment type and time, and SNPs in IL-1A (rs1800587), IL-1B (rs1143634), IL-1RN (rs419598), P2RX7 (rs1718119 and rs2230912), IRAK1 (rs1059703) and CASP1 (rs530537, rs580253 and rs554344). Chi-square test, Student's t test, Wilcoxon test, Benjamin-Hochberg false discovery rate (FDR) adjustment and logistic regression were used to analyse the data. The significance level was defined as P < .05. RESULTS: We found that extraction treatment protocol and dental classification displayed significant association with root resorption. Furthermore, the GG genotype of IL-1A rs1800587 variant (in individuals with an increased overjet) predisposed Caucasians to EARR. While CASP1 (rs530537) variant may contribute to the risk of root resorption, it was not statistically significant after FDR adjustment (P = .09). CONCLUSIONS: Both patient- and treatment-related factors contributed to EARR.

Non-syndromic hypodontia of maxillary lateral incisors and its association with other dental anomalies.

BACKGROUND: Tooth agenesis (TA) is the developmental absence of one or more teeth and is the most common craniofacial disorder in humans. Maxillary lateral incisor agenesis (MLIA) is a specific subtype of TA and can have esthetic, functional, and psychosocial implications for patients. The aim of this study was to evaluate the prevalence of MLIA amongst patients with non-syndromic tooth agenesis, as well as its association with other dental anomalies. MATERIALS AND METHODS: The dental records of 240 patients with non-syndromic congenitally missing teeth treated at the University of Alabama at Birmingham Department of Orthodontics were reviewed. Dolphin Imaging software was used to identify missing teeth, microdonts, peg laterals, impactions, and transpositions. Data were analyzed using chi-square or Fisher's exact test. All the tests were two-sided at the significance level of 0.05 (SAS 9.4). RESULTS: In the patient cohort, MLIA prevalence was 37.5% (second most common) and no gender or ethnic differences were identified. We also observed the bilaterally missing lateral incisors more frequently than the unilateral presentation (p = 0.0006). Additionally, 62.5% of patients with unilateral MLIA displayed a contralateral tooth that was a peg (p = 0.0001); however, no association was found with other microdonts. Furthermore, of the 90 patients missing at least one maxillary lateral incisor, 42.2% were missing another tooth type and 10% of MLIA patients also had an impacted tooth (mainly maxillary canines). However, these were not statistically significant. Finally, no transposed teeth were found in our patients. CONCLUSIONS: This study found that maxillary lateral incisors were the second most frequently missing teeth. When clinicians diagnose congenital absence of a maxillary lateral incisor, the patient should be evaluated for other missing teeth, peg lateral incisors, or potential impactions, especially maxillary canines.

Esthetic considerations in an orthodontic-orthognathic patient with Class III skeletal malocclusion.

Esthetics is one of the most important considerations in developing an orthodontic-orthognathic treatment plan. For patients with a Class III skeletal pattern, this multidisciplinary treatment option is designed to achieve adequate skeletal and functional enhancements and a harmonious esthetic outcome. This case report describes the orthodontic-orthognathic treatment of a 25-year-old female with skeletal Class III malocclusion, maxillary retrognathism, and anterior crossbite. The surgical plan included a maxillary LeFort I osteotomy and a mandibular bilateral sagittal split osteotomy. The double-jaw surgery combined with the orthodontic treatment improved her skeletal jaw relationship and occlusal function and resulted in excellent proportional facial esthetics.

In vitro comparison of wear of three orthodontic bite materials and opposing enamel.

OBJECTIVE: Orthodontic bite turbos are used to separate the maxillary and mandibular arch when disocclusion is needed for brackets placement or extrusion of teeth. Bite turbos should have adequate wear resistance to maintain disocclusion but also avoid abrasion of the opposing enamel. The objective of this study was to measure the wear of three materials used as bite turbos and opposing enamel wear. MATERIALS AND METHODS: 10mm×8mm×4mm specimens (n=8) of Transbond™LR (3M™) Transbond™ Plus (3M™) and Triad®gel (Dentsply) were prepared in silicone molds. Cusps of extracted premolars were prepared to a standard cone shape. Extracted maxillary incisors were used as reference for flat enamel surfaces. The experiments were performed on the modified UAB wear testing device at 20N for 200,000 cycles at 1Hz. All surfaces were scanned with a non-contact profilometer at 10micron resolution. Volumetric wear was measured with superimposition software and data analysed with one-way ANOVA and Tukey post-hoc. RESULTS: Significant differences were seen in the wear of materials and opposing enamels (P<.01). Material wear ranked: Triad®gel (.878±.196mm3)>Transbond™ Plus (.317±.062mm3)>Transbond™ LR (.136±.027mm3)>Enamel (.053±.04mm3). Opposing enamel ranked: Transbond™ LR (.158±.086mm3)=Enamel (.128±.035mm3)=Transbond™ Plus (.126±.025mm3)>Triad®gel (.039±.008mm3). CONCLUSIONS: All bite turbo materials wore more than natural enamel but caused equal or less wear to opposing enamel than tooth-tooth contact. Triad®gel underwent 2.5× and 6× the wear of Transbond™ Plus and Transbond™ LR respectively. The bite turbo material used may be selected based on preference for longevity.

Quantifying changes in incisor inclination before and after orthodontic treatment in class I, II, and III malocclusions.

BACKGROUND: This study was designed to determine if orthodontic treatment significantly changes the upper incisor position in Class I, II, and III dental and skeletal malocclusions. METHODS: Ninety nonextraction-treated patients were included in this retrospective cohort study and divided into three groups: Class I, Class II, and Class III. All cephalometric measurements (ANB, Wits, U1-PP, U1-SN, U1-NA, U1 perpendicular to FH and U1-L1) were taken using the Dolphin Management and Imaging Software, Version 05.05.5070.221436 (United States and Canada). RESULTS: The posttreatment values of ANB, Wits appraisal, U1-NA mm, U1-FH mm, IMPA and U1-L1° are statistically significant (P < 0.05) among the Class I, II, and III when compared with the normal values. Also ANB° changes after orthodontic treatment in Class I, II, and III were statistically significant with the greater changes in Class III malocclusion. CONCLUSIONS: There is a significant amount of dento-alveolar compensation for the maxillary incisors not only in patients with Class II and III but also in Class I malocclusions that underwent nonextraction treatments.

A randomized trial on the effects of root resorption after orthodontic treatment using pulsating force.

BACKGROUND: An orthodontic device that moves teeth with pulsating force was invented and underwent a single center, controlled, clinical trial to test its safety and efficacy for treatment. The device has a custom-made thermo-plastic mouthpiece which fits over the teeth with an inflatable silicone element. A console that measures and controls the pulsating force level in real-time controls the air pressure that delivers a pulsating force. In this study, the effect of the device on root resorption during orthodontic treatment was evaluated using 3D cone beam computed tomography and compared with a control group of patients who received Invisalign treatment. METHODS: Twenty-eight subjects were enrolled in the investigational arm and 15 in the control group. Subjects were followed until the average score of the mandibular and maxillary teeth achieved a Little's Irregularity Index of 1.5 mm or less. RESULTS: There were no adverse events reported throughout the study for either treatment arm. No clinically significant root resorption was observed for either group. The investigational device did not cause root resorption greater than the control group. Both devices produced a safety profile compared to current orthodontic techniques. CONCLUSION: The investigational device did not produce more root resorption than similar conventional orthodontic appliances. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03421886 . Registered 12 January 2018 - Retrospectively registered.

Evaluation of temporomandibular joint function after orthognathic surgery using a jaw tracker.

OBJECTIVE: It has been reported that temporomandibular joint (TMJ) function after orthognathic surgery differs from normal patients. Dysfunction of the joints occurs often even in the general public, with an incidence in the range of 20%-25%. Population-based studies among adults report that approximately 10%-15% have symptoms of pain and 5% of them had a perceived need for treatment. To date, no studies have reported on the evaluation of TMJ function after orthognathic surgery through the use of four-dimensional jaw tracking. DESIGN AND SETTING: This study evaluated TMJ function using such a device and information from a TMJ questionnaire. Sixteen orthognathic surgery patients and 17 controls were included in this study. Four-dimensional jaw tracking information was obtained using the SiCAT JMT device. Clinical signs and jaw function were evaluated. RESULTS: Within the limitations of the study, the following results were seen using the SICAT JMT+ jaw tracking device: (1) no significant differences were found in any of the millimetric measurements between the surgery patients and controls; (2) no significant difference was found in subjective reported symptoms of pain, clicking, crepitation, locking, stiffness, headaches and migraines between the groups; and (3)there was a significant difference in the popping of the joints for surgery and non-surgery groups. CONCLUSION: Jaw tracking did not detect significant differences in jaw function, but some clinical symptoms were present.

Ethnic differences in the root to crown ratios of the permanent dentition.

OBJECTIVE: Root resorption due to orthodontic tooth movement may adversely affect the root-crown (R/C) ratios of permanent teeth, especially in patients with Short Root Anomaly (SRA), a poorly understood disorder affecting root development. Evaluation of SRA R/C ratios to normal dentition would facilitate diagnosis and orthodontic treatment planning. However, reference values are not available for all ethnicities. Our goal was to determine R/C ratios of permanent teeth and their relationship to gender and ethnicity. SETTING/SAMPLE: A retrospective study of 333 patients (109 Caucasians, 112 African Americans and 112 Hispanics) from the University of Alabama at Birmingham School of Dentistry. MATERIALS/METHODS: Root lengths and crown heights were measured from panoramic radiographs of 6241 teeth using modified Lind's method. A linear mixed model was used to compare the R/C ratios of teeth among subgroups (gender, ethnicity). RESULTS: The mean R/C ratios varied from 1.80 to 2.21 for the maxillary teeth and 1.83-2.49 for the mandibular teeth. Gender differences in R/C ratios were found to be significant only for the lower central incisors (P < 0.05). Hispanics showed significantly lower ratios for most teeth compared to the other two groups (P < 0.05). There were significant differences in R/C ratios between African Americans and Caucasians in the upper lateral incisors, lower central incisors and lower first premolars (P < 0.05). CONCLUSION: Our results suggest that ethnicity is an important factor in determining the R/C ratios of permanent teeth. Therefore, when diagnosing developmental conditions such as SRA, ethnic group-specific reference values should be considered.

Surgical Management and Evaluation of the Craniofacial Growth and Morphology in Cleidocranial Dysplasia.

Cleidocranial dysplasia (CCD, MIM 119600) is a rare autosomal dominant disorder affecting bone, cartilage, craniofacial growth, and tooth formation leading to supernumerary teeth. Few reports delineate the genotype-phenotype correlations related to the variations in craniofacial morphology and patterning of the dentition and the complexity of treating patient's malocclusion. Successful management of the craniofacial deformities in patients with CCD requires a multidisciplinary team of healthcare specialists. Approximately 70% of patients are due to point mutations in RUNX2 and <20% due to copy number variations with the remainder unidentified. There is no literature to date, describing the orthognathic management of CCD patients with deletion in one of the RUNX2 alleles. The purpose of this study was to evaluate the craniofacial morphology and dental patterning in a 14-year-old Caucasian female with CCD resulting from a novel microdeletion of RUNX2 in 1 allele. The CCD patient with RUNX2 haploinsufficiency due to microdeletion had decreased craniofacial bone and ankyloses in the permanent dentition. An altered extraction protocol of supernumerary teeth was followed in this patient. Craniofacial growth and morphologic analysis demonstrated atypical skull shape, persistent metopic suture, and decreased mandibular size.

Short Root Anomaly - A Potential "Landmine" for Orthodontic and Orthognathic Surgery Treatment of Patients.

Short root anomaly (SRA) is a poorly understood developmental disorder and can significantly compromise the patient's dental treatment. This case report describes the treatment of a 15-year-old girl with SRA and discusses the implication of this disorder on orthodontic and orthognathic treatment of patients.

Maxillary Distraction Osteogenesis in Unilateral Cleft Lip and Palate Patients with Rigid External Distraction System.

AIM: Distraction osteogenesis (DO) is a treatment option for patients with maxillary hypoplasia secondary to cleft lip and palate (CLP). PURPOSE: The aim of this study is to present a technique for maxillary DO using Le Fort I osteotomy with rigid external distraction (RED) system. SUBJECTS AND METHODS: The patient presented in this paper was an Asian female with CLP aged 13 years and 6 months. She presented with severe midfacial deficiency with a Class III dental malocclusion with a negative overjet and concave facial profile. Cone-beam computed tomography images were recorded preoperatively and the operation performed involved a high Le Fort I osteotomy. The appliance fabricated was banded to upper first molars used for anchorage of the RED system. Distraction of the maxilla was initiated after 7-day latency period. RESULTS: Postoperative cephalometric analysis showed maxillary advancement anteriorly and superiorly, the total distraction treatment period was 10 days. The maxillary advancement was 10.5 mm and the SNA angle increased from 67.5° to 77.9°. Furthermore, the ANB angle changed from -9.8° to 1.6° and the occlusion changed from Class III to Class I. The profile of the face changed from concave to convex and a much better esthetic result was achieved. CONCLUSION: The study suggests RED system to be a reliable alternative procedure for the treatment of midfacial hypoplasia with or without cleft. Furthermore, it minimizes the risk of the surgical procedure and shortens the operating time.

NFI-C2 temporal-spatial expression and cellular localization pattern during tooth formation.

Currently, little is known regarding critical signaling pathways during later stages of tooth development, especially those associated with root formation. Nfi-c null mice, lacking molar roots, have implicated the transcription factor NFI-C as having an essential role in root development. Previously, we identified three NFI-C isoforms expressed in dental tissues with NFI-C2 being the major transcript. However, the expression pattern of the NFI-C2 protein is not characterized. In this study we performed in situ hybridization and immunohistochemistry using isoform specific probes. We show the production of a NFI-C2 peptide antibody, its characterization, the temporal-spatial expression pattern of the NFI-C2 protein during odontogenesis and sub-cellular localization in dental cells. Moderate NFI-C2 staining, as early as bud stage, was detected mostly in the condensing dental ectomesenchyme. This staining intensified within the dental pulp at later stages culminating in high expression in the dentin producing odontoblasts. The dental epithelium showed slight staining until cytodifferentiation of enamel organ into ameloblasts and stratum intermedium. During root formation NFI-C2 expression was high in the Hertwig's epithelial root sheath and later was found in the fully developed root and its supporting tissues. NFI-C2 cellular staining was cytosolic, associated with the Golgi, and nuclear. These data suggest a broader role for NFI-C during tooth formation than limited to root and periodontal ligament development.

Adenovirus gene transfer to amelogenesis imperfecta ameloblast-like cells.

To explore gene therapy strategies for amelogenesis imperfecta (AI), a human ameloblast-like cell population was established from third molars of an AI-affected patient. These cells were characterized by expression of cytokeratin 14, major enamel proteins and alkaline phosphatase staining. Suboptimal transduction of the ameloblast-like cells by an adenovirus type 5 (Ad5) vector was consistent with lower levels of the coxsackie-and-adenovirus receptor (CAR) on those cells relative to CAR-positive A549 cells. To overcome CAR -deficiency, we evaluated capsid-modified Ad5 vectors with various genetic capsid modifications including "pK7" and/or "RGD" motif-containing short peptides incorporated in the capsid protein fiber as well as fiber chimera with the Ad serotype 3 (Ad3) fiber "knob" domain. All fiber modifications provided an augmented transduction of AI-ameloblasts, revealed following vector dose normalization in A549 cells with a superior effect (up to 404-fold) of pK7/RGD double modification. This robust infectivity enhancement occurred through vector binding to both α(v)ß3/α(v)ß5 integrins and heparan sulfate proteoglycans (HSPGs) highly expressed by AI-ameloblasts as revealed by gene transfer blocking experiments. This work thus not only pioneers establishment of human AI ameloblast-like cell population as a model for in vitro studies but also reveals an optimal infectivity-enhancement strategy for a potential Ad5 vector-mediated gene therapy for AI.

Tissue- and cell-specific alternative splicing of NFIC.

Alternative splicing is an important mechanism for increasing genetic complexity leading to multiple transcripts from single genes and gene regulation through alternative promoters. Splicing often leads to unique tissue-specific patterns of mRNAs with specific biological functions. Nuclear factor I-C (NFI-C), a member of the NFI gene family, is expressed in numerous tissues including brain, liver, spleen and heart. However, the unique dental phenotype of Nfic(-/-) mice lacking molar roots demonstrates a critical role for this transcription factor in root formation. In humans, the NFI-C gene is alternatively spliced producing 4 isoforms. However, different spliced variants have not been studied in association with tissue specificity. The main objective of this study is to identify the NFI-C isoforms expressed in dental cells/tissues, comparing them to the spliced variants in nondental cells/tissues and to analyze their relative expression levels in various cell types. Using bioinformatics, we analyzed the NFI-C gene structure, identifying 2 potential alternative promoters driving expression of selective mRNA transcripts. Our studies show the expression of 3 NFI-C transcripts with the overall splicing pattern conserved between dental and nondental cells tested. Furthermore, by quantitative real-time PCR analysis, we found that although the relative levels of these transcripts were similar in dental and nondental cells, significant differences were observed within the dental cells tested. These are the first studies to analyze the expression of NFI-C isoforms in dental versus nondental cells/tissues, finding subtle cell-/tissue-specific expression patterns that could explain the dental phenotype of Nfic(-/-) mice.

Design of new benzoxazole-2-thione-derived inhibitors of Streptococcus pneumoniae hyaluronan lyase: structure of a complex with a 2-phenylindole.

The bacterial hyaluronan lyases (Hyals) that degrade hyaluronan, an important component of the extracellular matrix, are involved in microbial spread. Inhibitors of these enzymes are essential in investigation of the role of hyaluronan and Hyal in bacterial infections and constitute a new class of antibiotics against Hyal-producing bacteria. Recently, we identified 1,3-diacetylbenzimidazole-2-thione and related molecules as inhibitors of streptococcal Hyal. One of such compounds, 1-decyl-2-(4-sulfamoyloxyphenyl)-1-indol-6-yl sulfamate, was co-crystallized in a complex with Streptococcus pneumoniae Hyal and its structure elucidated. The resultant X-ray structure demonstrates that this inhibitor fits in the enzymatic active site via interactions resembling the binding mode of the natural hyaluronan substrate. X-ray structural analysis also indicates binding interactions with the catalytic residues and those of a catalytically essential hydrophobic patch. An IC50 value of 11 microM for Hyal from Streptococcus agalactiae (strain 4755) qualifies this phenylindole compound as one of the most potent Hyal inhibitors known to date. The structural data suggested a similar binding mode for N-(3-phenylpropionyl)-benzoxazole-2-thione. This new compound's inhibitory properties were confirmed resulting in discovery of yet another Hyal inhibitor (IC50 of 15 microM). These benzoxazole-2-thiones constitute a new class of inhibitors of bacterial Hyals and are well suited for further optimization of their selectivity, potency, and pharmacokinetic properties.

Structural studies and mechanism of Saccharomyces cerevisiae dolichyl-phosphate-mannose synthase: insights into the initial step of synthesis of dolichyl-phosphate-linked oligosaccharide chains in membranes of endoplasmic reticulum.

Dolichyl-phosphate-mannose (Dol-P-Man) synthase catalyzes the reversible formation of a key intermediate that is involved as a mannosyl donor in at least three different pathways for the synthesis of glycoconjugates important for eukaryotic development and viability. The enzyme is found associated with membranes of the endoplasmic reticulum (ER), where it transfers mannose from the water soluble cytoplasmic donor, guanosine 5'-diphosphate (GDP)-Man, to the membrane-bound, extremely hydrophobic, and long-chain polyisoprenoid acceptor, dolichyl-phosphate (Dol-P). The enzyme from Saccharomyces cerevisiae has been utilized to investigate the structure and activity of the protein and interactions of the enzyme with Dol-P and synthetic Dol-P analogs containing fluorescent probes. These interactions have been explored utilizing fluorescence resonance energy transfer (FRET) to establish intramolecular distances within the protein molecule as well as intermolecular distances to determine the localization of the active site and the hydrophobic substrate on the enzyme's surface. A three-dimensional (3D) model of the enzyme was produced with bound substrates, Dol-P, GDP-Man, and divalent cations to delineate the binding sites for these substrates as well as the catalytic site. The FRET analysis was used to characterize the functional properties of the enzyme and to evaluate its modeled structure. The data allowed for proposing a molecular mechanism of catalysis as an inverting mechanism of mannosyl residue transfer.

Overexpression of acid-sensing ion channel 1a in transgenic mice increases acquired fear-related behavior.

The acid-sensing ion channel 1a (ASIC1a) is abundantly expressed in the amygdala complex and other brain regions associated with fear. Studies of mice with a disrupted ASIC1 gene suggested that ASIC1a may contribute to learned fear. To test this hypothesis, we generated mice overexpressing human ASIC1a by using the pan-neuronal synapsin 1 promoter. Transgenic ASIC1a interacted with endogenous mouse ASIC1a and was distributed to the synaptosomal fraction of brain. Transgenic expression of ASIC1a also doubled neuronal acid-evoked cation currents. The amygdala showed prominent expression, and overexpressing ASIC1a enhanced fear conditioning, an animal model of acquired anxiety. These data raise the possibility that ASIC1a and H(+)-gated currents may contribute to the development of abnormal fear and to anxiety disorders in humans.

Acid-sensing ion channel 1 is localized in brain regions with high synaptic density and contributes to fear conditioning.

The acid-sensing ion channel, ASIC1, contributes to synaptic plasticity in the hippocampus and to hippocampus-dependent spatial memory. To explore the role of ASIC1 in brain, we examined the distribution of ASIC1 protein. Surprisingly, although ASIC1 was present in the hippocampal circuit, it was much more abundant in several areas outside the hippocampus. ASIC1 was enriched in areas with strong excitatory synaptic input such as the glomerulus of the olfactory bulb, whisker barrel cortex, cingulate cortex, striatum, nucleus accumbens, amygdala, and cerebellar cortex. Because ASIC1 levels were particularly high in the amygdala, we focused further on this area. We found that extracellular acidosis elicited a greater current density in amygdala neurons than hippocampal neurons and that disrupting the ASIC1 gene eliminated H+-evoked currents in the amygdala. We also tested the effect of ASIC1 on amygdala-dependent behavior; ASIC1-null mice displayed deficits in cue and context fear conditioning, yet baseline fear on the elevated plus maze was intact. These studies suggest that ASIC1 is distributed to regions supporting high levels of synaptic plasticity and contributes to the neural mechanisms of fear conditioning.

Insights into the catalytic mechanism of cofactor-independent phosphoglycerate mutase from X-ray crystallography, simulated dynamics and molecular modeling.

Phosphoglycerate mutases catalyze the isomerization of 2 and 3-phosphoglycerates, and are essential for glucose metabolism in most organisms. Here, we further characterize the 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (iPGM) from Bacillus stearothermophilus by determination of a high-resolution (1.4A) crystal structure of the wild-type enzyme and the crystal structure of its S62A mutant. The mutant structure surprisingly showed the replacement of one of the two catalytically essential manganese ions with a water molecule, offering an additional possible explanation for its lack of catalytic activity. Crystal structures invariably show substrate phosphoglycerate to be entirely buried in a deep cleft between the two iPGM domains. Flexibility analyses were therefore employed to reveal the likely route of substrate access to the catalytic site through an aperture created in the enzyme's surface during certain stages of the catalytic process. Several conserved residues lining this aperture may contribute to orientation of the substrate as it enters. Factors responsible for the retention of glycerate within the phosphoenzyme structure in the proposed mechanism are identified by molecular modeling of the glycerate complex of the phosphoenzyme. Taken together, these results allow for a better understanding of the mechanism of action of iPGMs. Many of the results are relevant to a series of evolutionarily related enzymes. These studies will facilitate the development of iPGM inhibitors which, due to the demonstrated importance of this enzyme in many bacteria, would be of great potential clinical significance.