Membrane protein density determining membrane fusion revealed by dynamic fluorescence imaging.

ABSTRACT Membrane fusion is fundamental to biological activity of cells, so the disclosure of its relevant mechanism has important implications for understanding various cell functions. Although artificial model systems have been developed to uncover the mechanism of membrane fusion, they cannot fully reflect the characteristics of membrane fusion in vivo. The modes of membrane fusion in vivo and vitro are distinctive, and the key factors determining the mode of membrane fusion remain unclear. Here, we used a dynamic fluorescence imaging method to detect the effect of membrane proteins distribution density on membrane fusion. Our data show that both pure phospholipid vesicles themselves and pure phospholipid vesicles and proteoliposomes with a lower proteins proportion are capable of fusing randomly, whereas pure phospholipid vesicles no longer fuse with proteoliposomes with a higher proteins proportion, indicating the dense membrane proteins may hinder membrane fusion. Moreover, through a comparative analysis on the interaction of pure phospholipid vesicles with the cell membrane, giant plasma membrane vesicles (GPMVs) and protein-free giant unilamellar vesicles (GUVs), respectively, we further confirm the inhibitory effect of dense membrane proteins on membrane fusion. Collectively, starting from the overall distribution characteristics of membrane proteins, we reveal that the membrane proteins distribution density influences the mode of membrane fusion. Our work lays a foundation for constructing membrane fusion models in vitro that can faithfully reflect natural membrane fusion process.