Direct observation of alpha-lactalbumin, adsorption and incorporation into lipid membrane and formation of lipid/protein hybrid structures

• Published in: Biochimica et biophysica acta. General subjects Vol. 1863; no. 5; pp. 784 - 794
• Main Authors: Rao, Estella, Foderà, Vito, Leone, Maurizio, Vetri, Valeria
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2019
• Subjects: adsorption; fluorescence; fluorescence microscopy; image analysis; lactalbumin; lipid bilayers; lipids; membrane fluidity; spectroscopy
• ISSN: 0304-4165; 1872-8006; 1872-8006
• DOI: 10.1016/j.bbagen.2019.02.005

The interaction between proteins and membranes is of great interest in biomedical and biotechnological research for its implication in many functional and dysfunctional processes. We present an experimental study on the interaction between model membranes and alpha-lactalbumin (α-La). α-La is widely studied for both its biological function and its anti-tumoral properties. We use advanced fluorescence microscopy and spectroscopy techniques to characterize α-La-membrane mechanisms of interaction and α-La-induced modifications of membranes when insertion of partially disordered regions of protein chains in the lipid bilayer is favored. Moreover, using fluorescence lifetime imaging, we are able to distinguish between protein adsorption and insertion in the membranes. Our results indicate that, upon addition of α-La to giant vesicles samples, protein is inserted into the lipid bilayer with rates that are concentration-dependent. The formation of heterogeneous hybrid protein-lipid co-aggregates, paralleled with protein conformational and structural changes, alters the membrane structure and morphology, leading to an increase in membrane fluidity. [Display omitted] •α-lactalbumin interacts with giant vesicles forming hybrid protein/lipid structures•Molten Globule α-lactalbumin addition to giant vesicles causes membrane reorganisation in a concentration dependent manner•FLIM and “Phasor Approach” allow distinguishing and mapping protein adsorption and insertion in the membrane•Laurdan dye may directly interact with proteins possibly causing artifacts.