Biomedical subjects

Christian D Santangelo

Publications and source records attributed to Christian D Santangelo.

4 recordsLinked to original sources

PubMed2006

Computing counterion densities at intermediate coupling.

By decomposing the Coulomb interaction into a long-distance component appropriate for mean-field theory, and a non-mean-field short distance component, we compute the counterion density near a charged surface for all values of the counterion coupling parameter. A modified strong-coupling expansion that is manifestly finite at all coupling strengths is used to treat the short-distance component. We find a nonperturbative correction related to the lateral counterion correlations that modifies the density at intermediate coupling.

Journal Article↗

PubMed2006

Elliptic phases: a study of the nonlinear elasticity of twist-grain boundaries.

We develop an explicit and tractable representation of a twist-grain-boundary phase of a smectic-A liquid crystal. This allows us to calculate the interaction energy between grain boundaries and the relative contributions from the bending and compression deformations. We discuss the special stability of the pi/2 grain boundaries and discuss the relation of this structure to the Schwarz D surface.

Biomechanical Phenomena↗

PubMed2005

Pore formation in fluctuating membranes.

We study the nucleation of a single pore in a fluctuating lipid membrane, specifically taking into account the membrane fluctuations, as well as the shape fluctuations of the pore. For large enough pores, the nucleation free energy is well-described by shifts in the effective membrane surface tension and the pore line tension. Using our framework, we derive the stability criteria for the various pore formation regimes. In addition to the well-known large-tension regime from the classical nucleation theory of pores, we also find a low-tension regime in which the effective line and surface tensions can change sign from their bare values. The latter scenario takes place at sufficiently high temperatures, where the opening of a stable pore of finite size is entropically favorable.

Journal Article↗

PubMed2004

Tau induces cooperative Taxol binding to microtubules.

Taxol and tau are two ligands that stabilize the microtubule (MT) lattice. Taxol is an anti-mitotic drug that binds beta tubulin in the MT interior. Tau is a MT-associated protein that binds both alpha and beta tubulin on the MT exterior. Both Taxol and tau reduce MT dynamics and promote tubulin polymerization. Tau alone also acts to bundle, stiffen, and space MTs. A structural study recently suggested that Taxol and tau may interact by binding to the same site. Using fluorescence recovery after photobleaching, we find that tau induces Taxol to bind MTs cooperatively depending on the tau concentration. We develop a model that correctly fits the data in the absence of tau, yields the equilibrium dissociation constant of approximately 2 microM, and determines the escape rate of Taxol through one pore to be 1.7 x 10(3) (M x s)(-1). Extension of the model yields a measure of Taxol cooperativity with a Hill coefficient of at least 15 when tau is present at a 1:1 molar ratio with tubulin.

Animals↗