Recognition of C-terminal amino acids in tubulin by pore loops in Spastin is important for microtubule severing

Spastin, an AAA ATPase mutated in the neurodegenerative disease hereditary spastic paraplegia, severs microtubules. Many other AAA proteins form ring-shaped hexamers and contain pore loops, which project into the ring's central cavity and act as ratchets that pull on target proteins, leading, in some cases, to conformational changes. We show that Spastin assembles into a hexamer and that loops within the central pore recognize C-terminal amino acids of tubulin. Key pore loop amino acids are required for severing, including one altered by a disease-associated mutation. We also show that Spastin contains a second microtubule binding domain that makes a distinct interaction with microtubules and is required for severing. Given that Spastin engages the MT in two places and that both interactions are required for severing, we propose that severing occurs by forces exerted on the C-terminal tail of tubulin, which results in a conformational change in tubulin, which releases it from the polymer

Analytical Ultracentrifugation: Sedimentation Velocity and Sedimentation Equilibrium

Analytical ultracentrifugation (AUC) is a versatile and powerful method for the quantitative analysis of macromolecules in solution. AUC has broad applications for the study of biomacromolecules in a wide range of solvents and over a wide range of solute concentrations. Three optical systems are available for the analytical ultracentrifuge (absorbance, interference, and fluorescence) that permit precise and selective observation of sedimentation in real time. In particular, the fluorescence system provides a new way to extend the scope of AUC to probe the behavior of biological molecules in complex mixtures and at high solute concentrations. In sedimentation velocity (SV), the movement of solutes in high centrifugal fields is interpreted using hydrodynamic theory to define the size, shape, and interactions of macromolecules. Sedimentation equilibrium (SE) is a thermodynamic method where equilibrium concentration gradients at lower centrifugal fields are analyzed to define molecule mass, assembly stoichiometry, association constants, and solution nonideality. Using specialized sample cells and modern analysis software, researchers can use SV to determine the homogeneity of a sample and define whether it undergoes concentration‐dependent association reactions. Subsequently, more thorough model‐dependent analysis of velocity and equilibrium experiments can provide a detailed picture of the nature of the species present in solution and their interactions

Characterization of the neuron-specific L1-CAM cytoplasmic tail: naturally disordered in solution it exercises different binding modes for different adaptor proteins

L1, a highly conserved transmembrane glycoprotein member of the immunoglobulin superfamily of cell adhesion molecules, mediates many developmental processes in the nervous system. Here we present the biophysical characterization and the binding properties of the least structurally defined part of this receptor: its cytoplasmic tail (CT). We have shown by analytical ultracentrifugation and dynamic light scattering experiments that it is mostly monomeric and unstructured in aqueous solution. We have defined by nuclear magnetic resonance the molecular details of L1-CT binding to two major targets: a membrane-cytoskeletal linker (MCL), ezrin, and an endocytosis mediator, AP2. Surprisingly, in addition to the two previously identified ezrin binding motifs, the juxtamembrane and the (1176)YRSLE regions, we have discovered a third one, a part of which has been previously associated with binding to another MCL, ankyrin. For the L1 interaction with AP2 we have determined the precise interaction region surrounding the (1176)YRSLE binding site and that this overlaps with the second ezrin binding site. In addition, we have shown that the juxtamembrane region of L1-CT has some binding affinity to AP2-mu2, although the specificity of this interaction needs further investigation. These data indicate that L1-CT belongs to the class of intrinsically disordered proteins. Endogenous flexibility of L1-CT might play an important role in dynamic regulation of intracellular signaling: the ability of cytoplasmic tails to accommodate different targets has the potential to fine-tune signal transduction via cell surface receptors

Does tamsulosin decrease postoperative urinary retention in spine surgery? A double-blind, randomized controlled trial

OBJECTIVE: The authors\u27 objective was to determine whether preoperative administration of tamsulosin decreases postoperative urinary retention after spine surgery. METHODS: In this randomized, double-blind, placebo-controlled clinical trial performed at a single institution between 2016 and 2019, eligible males aged 50 to 85 years were administered tamsulosin or placebo for 5 days prior to elective spine surgery. Patients were excluded if they were taking alpha adrenergic blocking drugs; were allergic to tamsulosin, lactose, or sulfa drugs; had a preexisting indwelling urinary catheter, orthostatic hypotension, history of urological surgery, or renal failure; or were scheduled for cataract surgery within 2 weeks. Screening identified 1051 eligible patients (140 declined participation, 150 did not meet the inclusion criteria, and 151 did not enroll for other reasons). A total of 610 patients were randomly assigned to receive 0.4 mg oral tamsulosin or an identical placebo capsule for 5 days preoperatively and 2 days postoperatively. RESULTS: A total of 497 patients were included in the final statistical analysis. The overall rate of postoperative urinary retention was 9.7%, and tamsulosin had no observed effect on reducing the rate of postoperative urinary retention as compared with placebo (9.4% vs 9.9%, p = 0.96). There were no significant differences in the reported adverse events between groups. Multivariate logistic regression was performed to model the effects of patient, surgical, and anesthetic factors on postoperative urinary retention, and the study drug remained an insignificant factor. CONCLUSIONS: This study did not detect an effect of perioperative tamsulosin on reducing the rate of postoperative urinary retention in male patients aged 50 to 85 years who underwent elective spine surgery. This study does not support the routine use of tamsulosin to reduce postoperative urinary retention in patients without a previous prescription. It is unknown if subpopulations exist for which prophylactic tamsulosin may reduce postoperative urinary retention