Effect of SP-C and its palmitoylation state on membrane fragmentation and vesicle uptake
Moran Lalangui, Mishelle, Jesus Perez-Gil, and Begoña Garcia-Alvarez. 2022. “Effect of SP-C and Its Palmitoylation State on Membrane Fragmentation and Vesicle Uptake.” Biophysical Journal 121 (3): 463a. https://doi.org/10.1016/j.bpj.2021.11.477.
One of the largest surfaces of the human body in contact with the environment is the respiratory epithelium, constituted by different specialized cells. Alveolar type I cells are involved in gas exchange whereas alveolar type II cells prevent the alveoli from collapsing due to the synthesis and secretion of lung surfactant (LS). This lipid-protein complex covers the alveolar surface and reduces surface tension at the air-liquid interface. LS, the first element in contact with inhaled air, is also involved in innate defense mechanisms. Surfactant protein C (SP-C) is a small hydrophobic transmembrane protein crucial for the biophysical function of LS. Different studies have revealed that the palmitoylation state of SP-C modulates important protein-lipid interactions within surfactant layers. Moreover, recent research has revealed that SP-C oligomerization, presumably through two structural motifs in SP-C sequence, could promote membrane fragmentation and enhance membrane vesicle alveolar uptake highlighting a key potential role of SP-C in LS homeostasis. In this work, we have analyzed the effect of palmitoylation on SP-C-promoted membrane fragmentation and vesicle uptake in the LS context. To do so, we have compared the behavior in different assays of the native palmitoylated protein and a recombinant SP-C version lacking palmitoyl chains, once reconstituted in two different lipid models mimicking LS membranes. Likewise, we have studied the implication of the proposed dimerization motifs in the SP-C sequence by testing synthetic peptides with selected sequence variations. Results from tunable resistive pulse sensing experiments suggest that both palmitoylation and the oligomerization state of SP-C are important to promote fission of membranes. Protein oligomerization and membrane fragmentation have been also analyzed with respect to membrane vesicle internalization by alveolar-derived cell lines, as evaluated by flow cytometry of cell cultures exposed to fluorescent lipid/protein complexes.View full article