Thermoplasmonic Vesicle Fusion Reveals Membrane Phase Segregation of Influenza Spike Proteins

Invagination of Giant Unilamellar Vesicles upon Membrane Mixing with Native Vesicles

We demonstrate rapid membrane mixing between GUVs of pure lipid compositions and membrane vesicles (MVs) isolated from the plasma membrane of Vero cells, resulting in the transfer of native lipids and proteins to the GUVs. The steps involved in the membrane mixing are docking followed by membrane fusion. We show that positively charged lipids of the GUVs are essential for the docking, and the native membrane components of MVs drive the fusion. The interleaflet and lateral asymmetry and a change in the membrane tension upon the membrane mixing trigger membrane invagination. We detected outward and inward invagination sites at the rim of the GUVs within 10-40 min of the membrane mixing. The extent of the invaginations depends on the cholesterol and sphingomyelin (SM) contents in the GUVs. Cholesterol content above a critical concentration disfavors membrane invaginations, and the SM lipid is an essential molecular factor for membrane invagination.

Biological Applications of Thermoplasmonics

Thermoplasmonics has emerged as an extraordinarily versatile tool with profound applications across various biological domains ranging from medical science to cell biology and biophysics. The key feature of nanoscale plasmonic heating involves remote activation of heating by applying laser irradiation to plasmonic nanostructures that are designed to optimally convert light into heat. This unique capability paves the way for a diverse array of applications, facilitating the exploration of critical biological processes such as cell differentiation, repair, signaling, and protein functionality, and the advancement of biosensing techniques. Of particular significance is the rapid heat cycling that can be achieved through thermoplasmonics, which has ushered in remarkable technical innovations such as accelerated amplification of DNA through quantitative reverse transcription polymerase chain reaction. Finally, medical applications of photothermal therapy have recently completed clinical trials with remarkable results in prostate cancer, which will inevitably lead to the implementation of photothermal therapy for a number of diseases in the future. Within this review, we offer a survey of the latest advancements in the burgeoning field of thermoplasmonics, with a keen emphasis on its transformative applications within the realm of biosciences.

Thermoplasmonic Vesicle Fusion Reveals Membrane Phase Segregation of Influenza Spike Proteins

Many cellular processes involve the lateral organization of integral and peripheral membrane proteins into nanoscale domains. Despite the biological significance, the mechanisms that facilitate membrane protein clustering into nanoscale lipid domains remain enigmatic. In cells, the analysis of membrane protein phase affinity is complicated by the size and temporal nature of ordered and disordered lipid domains. To overcome these limitations, we developed a method for delivering membrane proteins from transfected cells into phase-separated model membranes that combines optical trapping with thermoplasmonic-mediated membrane fusion and confocal imaging. Using this approach, we observed clear phase partitioning into the liquid disordered phase following the transfer of GFP-tagged influenza hemagglutinin and neuraminidase from transfected cell membranes to giant unilamellar vesicles. The generic platform presented here allows investigation of the phase affinity of any plasma membrane protein which can be labeled or tagged with a fluorescent marker.