Ion specific effects in bundling and depolymerization of taxol-stabilized microtubules

Needleman, Daniel J.,Ojeda-Lopez, Miguel A.,Raviv, Uri,Miller, Herbert P.,Li, Youli,Song, Chaeyeon,Feinstein, Stuart C.,Wilson, Leslie,Choi, Myung Chul,Safinya, Cyrus R. The Royal Society of Chemistry 2013 Faraday discussions Vol.166 No.-

<P>Microtubules (MTs) are nanometer scale hollow cylindrical biological polyelectrolytes. They are assembled from α/β-tubulin dimers, which stack to form protofilaments (PFs) with lateral interactions between PFs resulting in the curved MT. In cells, MTs and their assemblies are critical components in a range of functions from providing tracks for the transport of cargo to forming the spindle structure during mitosis. Previous studies have shown that while cations with valence equal to or larger than 3+ tend to assemble tight 3D bundles of taxol-stabilized MTs, certain divalent cations induce relatively loose 2D bundles of different symmetry (D. J. Needleman <I>et al.</I>, <I>Proc. Natl. Acad. Sci. U. S. A.</I>, 2004, <B>101</B>, 16099). Similarly, divalent cations form 2D bundles of DNA adsorbed on cationic membranes (I. Koltover <I>et al.</I>, <I>Proc. Natl. Acad. Sci. U. S. A.</I>, 2000, <B>97</B>, 14046). The bundling behavior for these biological polyelectrolyte systems is qualitatively in agreement with current theory. Here, we present results which show that, unlike the case for DNA adsorbed on cationic membranes, bundling of taxol-stabilized MTs occurs only for certain divalent cations above a critical ion concentration (<I>e.g.</I> Ca<SUP>2+</SUP>, Sr<SUP>2+</SUP>, Ba<SUP>2+</SUP>). Instead, many divalent cations pre-empt the bundling transition and depolymerize taxol-stabilized MTs at a lower counterion concentration. Although previous cryogenic TEM has shown that, in the absence of taxol, Ca<SUP>2+</SUP> depolymerizes MTs assembling in buffers containing GTP (guanosine triphosphate), our finding is surprising given the known stabilizing effects of taxol on GDP (guanosine diphosphate)-MTs. The ion concentration required for MT depolymerization decreases with increasing atomic number for the divalents Mg<SUP>2+</SUP>, Mn<SUP>2+</SUP>, Co<SUP>2+</SUP>, and Zn<SUP>2+</SUP>. GdCl<SUB>3</SUB> (3+) is found to be extremely efficient at MT depolymerization requiring ion concentrations of about 1 mM, while oligolysine (2+), is observed not to depolymerize MTs at concentrations as high as 144 mM. The surprising MT depolymerization results are discussed in the context of divalents either disrupting lateral interactions between PFs (which are strengthened for taxol containing β-tubulin), or interfering with taxol's ability to induce flexibility at the interface between two tubulin dimers in the same PF (which has been recently suggested as a mechanism by which taxol stabilizes MTs post-hydrolysis with the induced flexibility counteracting the kink between GDP-tubulin dimers in a PF).</P>

Rapid dislocation-density mapping of as-cut crystalline silicon wafers

Needleman, D. B.,Choi1, H.,Powell1, D. M.,Buonassisi, T. John Wiley Sons, Ltd 2013 Physica status solidi. PSS-RRL. Rapid Research Let Vol.7 No.12

Nonlocal Approach in Evaluating Strain Localization Behaviors of Voided Ductile Materials

Kim, Young-suk,Needleman A. 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.4

Finite element analysis of the strain localization behaviors of a voided ductile material has been performed using a non-local plasticity, in which the yield strength depends on both an equivalent plastic strain measure (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and Characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converges to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also showed that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.

Nanoscale Assembly in Biological Systems: From Neuronal Cytoskeletal Proteins to Curvature Stabilizing Lipids

Safinya, Cyrus R.,Raviv, Uri,Needleman, Daniel J.,Zidovska, Alexandra,Choi, Myung Chul,Ojeda‐,Lopez, Miguel A.,Ewert, Kai K.,Li, Youli,Miller, Herbert P.,Quispe, Joel,Carragher, Bridget,Potter, WILEY‐VCH Verlag 2011 ADVANCED MATERIALS Vol.23 No.20

<P><B>Abstract</B></P><P>The review will describe experiments inspired by the rich variety of bundles and networks of interacting microtubules (MT), neurofilaments, and filamentous‐actin in neurons where the nature of the interactions, structures, and structure‐function correlations remain poorly understood. We describe how three‐dimensional (3D) MT bundles and 2D MT bundles may assemble, in cell free systems in the presence of counter‐ions, revealing structures not predicted by polyelectrolyte theories. Interestingly, experiments reveal that the neuronal protein tau, an abundant MT‐associated‐protein in axons, modulates the MT diameter providing insight for the control of geometric parameters in bio‐ nanotechnology. In another set of experiments we describe lipid‐protein‐nanotubes, and lipid nano‐ tubes and rods, resulting from membrane shape evolution processes involving protein templates and curvature stabilizing lipids. Similar membrane shape changes, occurring in cells for the purpose of specific functions, are induced by interactions between membranes and proteins. The biological materials systems described have applications in bio‐nanotechnology.</P>

Anatomy Versus Physiology: Is Breast Lymphatic Drainage to the Internal Thoracic (Internal Mammary) Lymphatic System Clinically Relevant?

Priscilla Machado,Ji-Bin Liu,Laurence Needleman,Christine Lee,Flemming Forsberg 한국유방암학회 2023 Journal of breast cancer Vol.26 No.3

Approximately 15%−25% of breast lymphatic drainage passes through the internal thoracic (internal mammary) lymphatic system, draining the inner quadrants of the breast. This study aimed to use lymphosonography to identify sentinel lymph nodes (SLNs) in the axillary and internal thoracic lymphatic systems in patients with breast cancer. Seventy-nine patients received subcutaneous ultrasound contrast agent injections around the tumor. Lymphosonography was used to identify SLNs. In 14 of the 79 patients (17.7%), the tumor was located in the inner quadrant of the breast. Lymphosonography identified 217 SLNs in 79 patients, averaging 2.7 SLNs per patient. The 217 identified SLNs in the 79 patients were located in the axillary lymphatic system; none were located in the internal thoracic (internal mammary) lymphatic system, although it was expected in two to four patients (i.e., 4–11 SLNs). These results implied that SLNs associated with breast cancer are predominantly located in the axillary lymphatic system.

Human Microtubule-Associated-Protein Tau Regulates the Number of Protofilaments in Microtubules: A Synchrotron X-Ray Scattering Study

Choi, M.C.,Raviv, U.,Miller, H.P.,Gaylord, M.R.,Kiris, E.,Ventimiglia, D.,Needleman, D.J.,Kim, M.W.,Wilson, L.,Feinstein, S.C.,Safinya, C.R. Biophysical Society ; Published for the Biophysica 2009 Biophysical journal Vol.97 No.2

Microtubules (MTs), a major component of the eukaryotic cytoskeleton, are 25 nm protein nanotubes with walls comprised of assembled protofilaments built from αβ heterodimeric tubulin. In neural cells, different isoforms of the microtubule-associated-protein (MAP) tau regulate tubulin assembly and MT stability. Using synchrotron small angle x-ray scattering (SAXS), we have examined the effects of all six naturally occurring central nervous system tau isoforms on the assembly structure of taxol-stabilized MTs. Most notably, we found that tau regulates the distribution of protofilament numbers in MTs as reflected in the observed increase in the average radius <R<SUP>MT</SUP>> of MTs with increasing Φ, the tau/tubulin-dimer molar ratio. Within experimental scatter, the change in <R<SUP>MT</SUP>> seems to be isoform independent. Significantly, <R<SUP>MT</SUP>> was observed to rapidly increase for 0 < Φ < 0.2 and saturate for Φ between 0.2-0.5. Thus, a local shape distortion of the tubulin dimer on tau binding, at coverages much less than a monolayer, is spread collectively over many dimers on the scale of protofilaments. This implies that tau regulates the shape of protofilaments and thus the spontaneous curvature C<SUB>o</SUB><SUP>MT</SUP> of MTs leading to changes in the curvature C<SUP>MT</SUP> (=1/R<SUP>MT</SUP>). An important biological implication of these findings is a possible allosteric role for tau where the tau-induced shape changes of the MT surface may effect the MT binding activity of other MAPs present in neurons. Furthermore, the results, which provide insight into the regulation of the elastic properties of MTs by tau, may also impact biomaterials applications requiring radial size-controlled nanotubes.