Periplasmic Binding Protein Dimer Has a Second Allosteric Event Tied to Ligand Binding.

The ligand-induced conformational changes of periplasmic binding proteins (PBP) play a key role in the acquisition of metabolites in ATP binding cassette (ABC) transport systems. This conformational change allows for differential recognition of the ligand occupancy of the PBP by the ABC transporter. This minimizes futile ATP hydrolysis in the transporter, a phenomenon in which ATP hydrolysis is not coupled to metabolite transport. In many systems, the PBP conformational change is insufficient at eliminating futile ATP hydrolysis. Here we identify an additional state of the PBP that is also allosterically regulated by the ligand. Ligand binding to the homodimeric apo PBP leads to a tightening of the interface α-helices so that the hydrogen bonding pattern shifts to that of a 310 helix, in-turn altering the contacts and the dynamics of the protein interface so that the monomer exists in the presence of ligand.

3D-Printed Model in Preoperative Planning of Sciatic Nerve Decompression Because of Heterotopic Ossification: A Case Report.

CASE: A 31-year-old patient presented with an encapsulated sciatic nerve secondary to extensive hip heterotopic ossification (HO), which prevented visualization of a safe osteotomy site to avoid nerve damage. The 3D-printed model demonstrated an easily identifiable osseous reference point along the inferior aspect of the heterotopic mass, allowing for a vertical osteotomy to be safely performed. CONCLUSION: HO is associated with loss of normal anatomic topography. The current case report illustrates the use of a 3D-printed model to identify pertinent anatomic landmarks required for safe decompression of an encapsulated sciatic nerve within the anatomic region of the hip.

Validation of Impaction Grafting for Single-Level Transforaminal Lumbar Interbody Fusion-Technical Pearls and MicroCT Analysis.

STUDY DESIGN: Cadaveric study. BACKGROUND CONTEXT: Transforaminal lumbar interbody fusion (TLIF) represents a well-documented operative surgical technique utilized in the management of lumbar pathology requiring interbody arthrodesis. The microstructural properties of impaction grafting (IG) after TLIF has yet to be reported. PURPOSE: The current study was designed first, to quantify the degree, to which IG augmentation would increase intrabody final bone volume and bone graft surface contact area with the endplates; secondly to quantify the volumes of locally harvested bone and bone needed for maximal impaction. MATERIALS AND METHODS: Three cadaveric lumbosacral spine specimens were dissected into L1-L2, L3-L4, and L5-S1 motion segments for a total of 9 functional spinal units. Each interbody unit underwent a TLIF procedure with the implantation of an interbody spacer containing autogenous morselized bone. Microcomputed tomography scans were then performed to evaluate the final bone volume and bone surface contact area (BSCA). Subsequently, IG augmented TLIF procedure was carried and microcomputed tomography scans were repeated. RESULTS: IG augmentation of TLIF exhibited a 346% increase in final bone volume (TLIF: 0.30 ± 0.07 cm 3 ; IG-TLIF: 1.34 ± 0.42 cm 3 ; P < 0.05) and a 152% increase in BSCA (TLIF: 45.06 ± 15.47%; IG-TLIF: 68.28 ± 6.85%; P < 0.05) when compared with the nonimpacted TLIF treatment. In addition, the average amount of autogenous bone collected was 8.21±2.08 cm 3 , which sufficiently fulfilled the requirements for bone grafting (TLIF: 1.23 ± 0.40 cm 3 ; IG-TLIF 6.42 ± 1.20 cm 3 ). CONCLUSIONS: IG augmentation of TLIF significantly improved final bone volume in the disc space and BSCA with vertebral endplates in vitro. CLINICAL SIGNIFICANCE: Greater BSCA and final volume of bone graft reflect promisingly on their potential to increase fusion rates. Clinical studies will be needed to corroborate these findings.