A semi-flexible model prediction for the polymerization force exerted by a living F-actin filament on a fixed wall.

نویسندگان

  • Carlo Pierleoni
  • Giovanni Ciccotti
  • Jean-Paul Ryckaert
چکیده

We consider a single living semi-flexible filament with persistence length ℓp in chemical equilibrium with a solution of free monomers at fixed monomer chemical potential μ1 and fixed temperature T. While one end of the filament is chemically active with single monomer (de)polymerization steps, the other end is grafted normally to a rigid wall to mimic a rigid network from which the filament under consideration emerges. A second rigid wall, parallel to the grafting wall, is fixed at distance L < < ℓp from the filament seed. In supercritical conditions where monomer density ρ1 is higher than the critical density ρ1c, the filament tends to polymerize and impinges onto the second surface which, in suitable conditions (non-escaping filament regime), stops the filament growth. We first establish the grand-potential Ω(μ1, T, L) of this system treated as an ideal reactive mixture, and derive some general properties, in particular the filament size distribution and the force exerted by the living filament on the obstacle wall. We apply this formalism to the semi-flexible, living, discrete Wormlike chain model with step size d and persistence length ℓp, hitting a hard wall. Explicit properties require the computation of the mean force f̄i(L) exerted by the wall at L and associated potential f̄i(L)=-dWi(L)/dL on a filament of fixed size i. By original Monte-Carlo calculations for few filament lengths in a wide range of compression, we justify the use of the weak bending universal expressions of Gholami et al. [Phys. Rev. E 74, 041803 (2006)] over the whole non-escaping filament regime. For a filament of size i with contour length Lc = (i - 1) d, this universal form is rapidly growing from zero (non-compression state) to the buckling value fb(Lc,ℓp)=π(2)kBTℓp4Lc (2) over a compression range much narrower than the size d of a monomer. Employing this universal form for living filaments, we find that the average force exerted by a living filament on a wall at distance L is in practice L independent and very close to the value of the stalling force Fs (H)=(kBT/d)ln(ρˆ1) predicted by Hill, this expression being strictly valid in the rigid filament limit. The average filament force results from the product of the cumulative size fraction x=x(L,ℓp,ρˆ1), where the filament is in contact with the wall, times the buckling force on a filament of size Lc ≈ L, namely, Fs (H)=xfb(L;ℓp). The observed L independence of Fs (H) implies that x ∝ L(-2) for given (ℓp,ρˆ1) and x∝lnρˆ1 for given (ℓp, L). At fixed (L,ρˆ1), one also has x∝ℓp (-1) which indicates that the rigid filament limit ℓp → ∞ is a singular limit in which an infinite force has zero weight. Finally, we derive the physically relevant threshold for filament escaping in the case of actin filaments.

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Modeling the evolution of cells outgrowth due to the force exerted by actins

Motility and membrane deformation are crucial to motile cells. Therefore formation of protrusion in the membrane has been the subject of various studies. The stable shape of the membrane and also its movements are controlled by the forces exerted by actin filaments. In order to study the protrusion behavior, we represented a toy model based on actin filaments polar characteristic and elastic ch...

متن کامل

Particle-Based Modeling of Living Actin Filaments in an Optical Trap

We report a coarse-grained molecular dynamics simulation study of a bundle of parallel actin filaments under supercritical conditions pressing against a loaded mobile wall using a particle-based approach where each particle represents an actin unit. The filaments are grafted to a fixed wall at one end and are reactive at the other end, where they can perform single monomer (de)polymerization st...

متن کامل

Compression forces generated by actin comet tails on lipid vesicles.

Polymerizing networks of actin filaments generate force for a variety of movements in living cells, including protrusion of filopodia and lamellipodia, intra- and intercellular motility of certain bacterial and viral pathogens, and motility of endocytic vesicles and other membrane-bound organelles. During actin-based motility, coexisting populations of actin filaments exert both pushing and ret...

متن کامل

A master equation approach to actin polymerization applied to endocytosis in yeast

We present a Master Equation approach to calculating polymerization dynamics and force generation by branched actin networks at membranes. The method treats the time evolution of the F-actin distribution in three dimensions, with branching included as a directional spreading term. It is validated by comparison with stochastic simulations of force generation by actin polymerization at obstacles ...

متن کامل

Actin-based propulsive forces and myosin-II-based contractile forces in migrating Dictyostelium cells.

It has been suggested that myosin II exerts traction forces at the posterior ends and retracting pseudopodia of migrating cells, but there is no direct evidence. Here, using a combination of total internal reflection fluorescence (TIRF) microscopy and force microscopy with a high spatial resolution of approximately 400 nm, we simultaneously recorded GFP-myosin II dynamics and traction forces un...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:
  • The Journal of chemical physics

دوره 143 14  شماره 

صفحات  -

تاریخ انتشار 2015