ABSTRACT
BACKGROUND:Transpedicular transdiscal lumbar screw is a new type of spinal minimally invasive internal fixation technology.Compared with traditional bilateral pedicle screws,only one screw is needed to fix one segment on one side.It has the characteristics of being more economical,less trauma and easy to operate.However,studies on the application of transpedicular transdiscal lumbar screws combined with transforaminal lumbar interbody fusion(TLIF)and fixation are still rare. OBJECTIVE:To evaluate the effect of TLIF combined with various surgery methods on stress distribution of cage,fixation,disc lower and endplate and range of motion of lumbar vertebrae by constructing three kinds of finite element models including modified TLIF(cage alone)model,modified TLIF combined with bilateral pedicle screw(cage+BPS)model and modified TLIF combined with bilateral transpedicular transdiscal lumbar screw(cage+BTPTDS)model. METHODS:The CT images of the adult lumbar spine were used to establish the three kinds of TLIF finite element models:cage alone,cage+BPS and cage+BTPTDS using software Mimics,Geomagic and SolidWorks.ANSYS Workbench was used to simulate the application of six different motion loads of human body flexion and extension,left and right bending,and left and right rotation to calculate stress distribution and the changes in the range of motion of the lumbar spine of the cage,fixation,endplate and disc of the three lumbar spine surgery models and to compare the effects of three surgical options on the biomechanical effects of the lumbar spine. RESULTS AND CONCLUSION:(1)The cage alone model,cage+BPS model and cage+BTPTDS model were constructed successfully.(2)In flexion and lateral bending conditions,the maximum stress of the cage of cage+BTPTDS model was smaller than that of the cage alone model and a little greater than that of the cage+BPS model.In the extension condition,the maximum stress of the cage of the cage+BPS model was obviously smaller than that of the other two models.When it came to rotating condition,the maximum stress of the cage in the cage+BPS model and the cage+BTPTDS model presented no obvious difference,which was both smaller than the cage alone model.(3)The maximum stress of fixation of the cage+BTPTDS model was obviously bigger than the cage+BPS model in flexion and extension conditions,close to the cage+BPS model in lateral bending conditions,and smaller than the cage+BPS model in rotation conditions.(4)The maximum stress of the lower endplate of the fusion segment of the cage+BPS model was between the two other models.(5)In terms of the range of motion,the cage+BTPTDS model presented no obvious difference with that of the cage+BPS model at flexion and extension,left and right bending,and left and right rotation.(6)It is concluded that modified TLIF combined with transpedicular transdiscal lumbar screw provides stable support for the vertebral body of the fusion segment,ensures the motion range of the lumbar spine and has a good biomechanical effect.
ABSTRACT
OBJECTIVE@#To develop a fast, sensitive and cost-effective method based on resonance light scattering (RLS) for characterization of protein solubility to facilitate detection of changes in solubility of mutant proteins.@*METHODS@#We examined the response curve of RLS intensities to the protein concentrations in synchronous scanning mode. The curve intersection points were searched to predict the maximal concentrations of the protein in dispersion state, which defined the solubility of the protein in this given state. Bovine serum albumin (BSA, 0-50 g/L) was used as the model to investigate the influences of pH values (6.5, 7.0, and 7.4) and salt concentrations (0.05, 0.10, 0.15, and 0.20 mol/L) on the determined solubility. The solubility of glutathione S-transferase isoenzymes alpha (GSTA, 0-27.0 g/L) and Mμ (GSTM, 0-20.0 g/L) were estimated for comparison. The RLS-based method was used to determine the solubility of uricase (MGU, 0-0.4 g/L) to provide assistance in improving the solubility of its mutants.@*RESULTS@#We identified two intersection points in the RLS response curves of the tested proteins, among which the lower one represented an approximation of the maximal concentration (or the solubility of the protein) in single molecular dispersion, and the higher one the saturated concentration of the protein in multiple molecular aggregation. In HEPES buffer, the two intersection points of BSA (isoelectric point 4.6) both increased with the increase of pH (6.5-7.4), and their values were ~1.2 g/L and ~33 g/L at pH 7.4, respectively; the latter concentration approached the solubility of commercial BSA in the same buffer at the same pH. The addition of NaCl reduced the values of the two intersection points, and increasing salt ion concentration decreased the values of the lower intersection points. Further characterizations of GSTA and GSTM showed that the low concentration intersection points of the two proteins were ~0.7 g/L and ~0.8 g/L, and their high concentration intersection points were ~10 g/L and ~11 g/L, respectively, both lower than those of BSA, indicating the feasibility of the direct characterization of protein solubility by RLS. The two concentration intersection points of MGU were 0.24 g/L and 0.30 g/L, respectively, and the low concentration intersection point of its selected mutant was increased by 2 times.@*CONCLUSIONS@#RLS allows direct characterization of the solubility of macromolecular proteins. This method, which is simple and sensitive and needs only a small amount of proteins, has a unique advantage for rapid comparison of solubility of low-abundance protein mutants.
Subject(s)
Hydrogen-Ion Concentration , Light , Scattering, Radiation , Solubility , Spectrum AnalysisABSTRACT
To explore the immobilization of target proteins for screening libraries of ligand mixtures, magnetic submicron particles (MSP) functionalized with Ni²⁺-NTA and carboxyl were compared for the immobilization of Mycobacterium tuberculosis dihydrofolate reductase (MtDHFR). MtDHFR fused with 6×His was expressed, purified and characterized for kinetics. MtDHFR was immobilized on Ni²⁺-NTA-functionalized MSP directly and carboxyl-functionalized MSP upon activation. The immobilization capacity, residual activity, thermostability and affinities for putative inhibitors were characterized. MtDHFR immobilized on Ni²⁺-NTA-functionalized MSP retained about 32% activity of the free one with the immobilization capacity of (93±12) mg/g of MSP (n=3). Ni²⁺ and EDTA synergistically inhibited MtDHFR activity, while Fe³⁺ had no obvious interference. MtDHFR immobilized on carboxyl-functionalized MSP retained (87±4)% activity of the free one with the immobilization capacity of (8.6±0.6) mg/g MSP (n=3). In 100 mmol/L HEPES (pH 7.0) containing 50 mmol/L KCl, there was no significant loss of the activities of the free and immobilized MtDHFR after storage at 0 °C for 16 h, but nearly 60% and 35% loss of their activities after storage at 25 °C for 16 h, respectively. The inhibition effects of methotrexate on the immobilized and free MtDHFR were consistent (P>0.05). The immobilization of MtDHFR on carboxyl-functionalized MSP was thus favorable for higher retained activity and better thermostability, with promise for rapid screening of its ligand mixtures.