Mikkel Jensen - Preliminary Oral Exam

When: April 8, 2011 (Fri), 10:00AM to 11:00AM (add to my calendar)
Location: PRB 365

This event is part of the Preliminary Oral Exam.

Title: Regulation of Actin Mechanics, Dynamics, and Structure by Associated Actin-Binding Proteins
Examining Committee: Ken Rothschild, Jeffrey Moore, Rama Bansil, Sid Redner, Robert Carey

Abstract:
We study the effect of two smooth muscle actin-binding proteins, calponin and caldesmon, on the mechanics, dynamics, and structure of filamentous actin. The bending rigidity of actin is determined by fluorescence microscopy of labeled actin filaments by treating the polymer as a worm-like chain. Through a correlation function analysis calponin is observed to reduce the actin persistence length, a result interpreted as a reduction of the Young’s modulus of the actin filament. Calponin is also observed to destabilize the actin filament, making it more susceptible to severing by external shear forces. These results are discussed in light of work published on the actin severing protein cofilin and are compared to the proposed model for actin severing by cofilin.
Furthermore, we observe the caldesmon subfragment H32K by electron microscopy to prolong a nascent state of the newly polymerized actin filament. Actin assembly is visualized by TIRF microscopy, and H32K is shown to not affect the rate of actin polymerization despite changes seen in bulk pyrene-fluorescence assays. Implications and future experiments addressing the functional importance of this structural state are outlined.
Actin has been proposed to have many structural states existing in equilibrium. We discuss the effects of both calponin and caldesmon in light of this hypothesis and discuss a connection between the internal structural states of actin and the mechanics and dynamics of the filament.

Best wishes to Mikkel!!