Fusion of Sendai Virus With Vesicles of Oligomerizable Lipids: A Microcalorimetric Analysis of Membrane Fusion

Abstract

Sendai virus fuses efficiently with small and large unilamellar vesicles of the lipid 1,2-di-nhexadecyloxypropyl-4-(beta-nitrostyryl) phosphate (DHPBNS) at pH 7.4 and 37°C, as shown by lipid mixing assays and electron microscopy. However, fusion is strongly inhibited by oligomerization of the head groups of DHPBNS in the bilayer vesicles. The enthalpy associated with fusion of Sendai virus with DHPBNS vesicles was measured by isothermal titration microcalorimetry, comparing titrations of Sendai virus into (i) solutions of DHPBNS vesicles (which fuse with the virus) and (ii) oligomerized DHPBNS vesicles (which do not fuse with the virus), respectively. The observed heat effect of fusion of Sendai virus with DHPBNS vesicles is strongly dependent on the buffer medium, reflecting a partial charge neutralization of the Sendai F and HN proteins upon insertion into the negatively-charged vesicle membrane. No buffer effect was observed for the titration of Sendai virus into oligomerized DHPBNS vesicles, indicating that inhibition of fusion is a result of inhibition of insertion of the fusion protein into the target membrane. Fusion of Sendai virus with DHPBNS vesicles is endothermic and entropy-driven. The positive enthalpy term is dominated by heat effects resulting from merging of the protein-rich viral envelope with the lipid vesicle bilayers rather than by the fusion of the viral with the vesicle bilayers per se.

Electron microscopic investigation of the morphology and calcium-induced fusion of lipid vesicles with an oligomerised inner leaflet

“…The amphiphilic compounds DDPBNS and DHPBNS are members of a family of synthetic lipids that provides a useful membrane mimetic system (Ravoo et al, 1996(Ravoo et al, , 1998(Ravoo et al, , 1999(Ravoo et al, , 2000. The molecular structures of DDPBNS and DHPBNS are presented in Fig.…”

“…It was found that fusion of small vesicles is associated with a small positive enthalpy and requires an entropic driving force. Furthermore, the fusion of vesicles of DHPBNS with Sendai virus was investigated (Ravoo et al, 2000). It was observed that vesicle-virus fusion is strongly inhibited by lipid head group oligomerisation.…”

The thermodynamics of simple biomembrane mimetic systems

“…[162234] As the integral heats of titration do not provide any information on transient states, the heat of fusion of the bilayers per se is small, and the heat effects observed should be mainly attributed to interactions of viral proteins with the target membrane. For example, a partial deprotonation of a viral protein on membrane fusion was detected by ITC using the buffer variation method (see section Isothermal titration calorimetry ).…”

“…For example, a partial deprotonation of a viral protein on membrane fusion was detected by ITC using the buffer variation method (see section Isothermal titration calorimetry ). [162] Also the enthalpy of proton-induced vesicle fusion was measured by ITC. [228] DSC studies of viral proteins have yielded important information on fusogenic protein states in viruses (see the next section).…”

Microcalorimetric Study on the Effect of Ce3+ on Halobacterium halobium R1

“…Because of these advantages, the microcalorimetric method may reveal more and newer details about the metabolism than the existing methods do. Therefore, the microcalorimetric method has been used in many fields of biological science [8][9][10]. It can be foreseen that the microcalorimetric technique will be used more and more wildly to understand the biological processes through this technique and other methods.…”