As a part of the German-Croatian bilateral project "Myelin protein impact on membrane phase state, morphology and structure" (DAAD-MZO), PhD student Matilde Accorsi from the Max Planck Institute in Potsdam, Germany visited RBI and presented her research in a lecture titled rane phase state, morphology and structure" doktorandica Matilde Accorsi posjetila je IRB i prezentirala svoja istraživanja na kolokviju naslova "Reconciling past and future research: a study on calcium as a protein-free fusogen in negatively-charged cell-sized vesicles".

Abstract:

n the late 20th century, calcium took on a new identity as an independent fusogen, when it was found to induce fusion in negatively-charged nanometric vesicles (large unilamellar vesicles, LUVs) even in the absence of proteins 1 . These studies are still a core part of membrane model fusion research and are frequently cited. While cell-sized lipid vesicles (giant unilamellar vesicles, GUVs) gained popularity in the 1990s as membrane model, they have not been the subject of an in-depth study about calcium-induced fusion. To investigate this matter, we developed an approach based on confocal microscopy and microfluidics (e.g. Fig. 1)2, 3 and explored how different GUV compositions respond to varying calcium concentrations and environmental conditions. We find that calcium can easily induce hemifusion with lipid mixing in negatively-charged GUVs, while full fusion with content mixing is rather rare and requires fine membrane composition and environmental control to attempt to curb membrane instability. Reconciling past research with modern models proves to be difficult in this case, as our results point to calcium as a less ubiquitous and more elusive fusogen than previously thought in pure lipid GUVs. To find a compromise between past and present models, we explore instead calcium as a protein-free fusogen in negatively-charged LUV to GUV fusion, a task that introduces new challenges and questions.