Coupling of lipid membrane elasticity and in-plane dynamics

Biomembranes exhibit liquid and solid features concomitantly with their in-plane fluidity and elasticity tightly regulated by cells. Here, we present experimental evidence supporting the existence of the dynamics-elasticity correlations for lipid membranes and propose a mechanism involving molecular packing densities to explain them. This paper thereby unifies, at the molecular level, the aspects of the continuum mechanics long used to model the two membrane features. This ultimately may elucidate the universal physical principles governing the cellular phenomena involving biomembranes.

Figure 1

The ESR spectra of (a) the Tempo PC-containing MLVs of DOPC and (b) the 16-PC-containing MLVs of equimolar $\mathrm{DOPC}+\mathrm{DOPE}$ with the spectral features quantified in (c), where ${\tau }_{R,s}$ (filled symbols) and ${\tau }_{R,mp}$ (empty symbols) are plotted as functions of temperature. (Shorter ${\tau }_R$'s reflect faster motions.) The inset is the blowup of the low-field resonance. The $2A_{max}$ is as defined in the figures for 293 K. Linear fittings are to guide the eyes.

Figure 2

The ESR spectra of (a) the Tempo PC-containing MLVs of $\mathrm{DOPC}+\mathrm{DOPE}$ in various molar ratios, (b) the 16-PC-containing MLVs of $\mathrm{DOPC}+\mathrm{DOPE}$ in various molar ratios, and (c) the 16-PC-containing MLVs of DOPC, di18:2 PC, or di18:3 PC at 313 K. The right panel is the blowup of the low-field resonance. The low-field resonance for equimolar $\mathrm{DOPC}+\mathrm{DOPE}$ [blue in (a)], 90:10 $\mathrm{DOPC}+\mathrm{DOPE}$ [black in (b)], and di18:3 PC [blue in (c)] is slightly narrower than those for the other samples in the respective figures, indicating the deceleration of the respective molecular segmental motions upon decreasing the DOPE content [in (a)], increasing the DOPE content [in (b)], and substituting DOPC for di18:3 [in (c)].

Figure 3

(a) ${\tau }_{R,s}$ and (b) ${\tau }_{R,mp}$ as functions of the DOPE fraction ${\mathrm{\Phi }}_{\mathrm{PE}}$ at different temperatures. Linear fittings are to guide the eyes.

Figure 4

${\tau }_{R,mp}$ as a function of the PC species for the MLVs of PC or equimolar $\mathrm{PC}+\mathrm{DOPE}$ at 303 K. Lines are to guide the eyes.

Figure 5

Relative differences in $g_E$, $|C_0|$, or $K_{cp}$ versus (a) ${\tau }_{R,s}$ and (b) ${\tau }_{R,mp}$ at 303 K. The inset enlarges the region of small relative differences. Fittings are to guide the eyes.