Conformational changes, from β-strand to α-helix, of the fatty acid-binding protein ReP1-NCXSQ in anionic lipid membranes: dependence with the vesicle curvature
We studied the conformational changes of the fatty acid-binding protein ReP1-NCXSQ in the interface of anionic lipid membranes. ReP1-NCXSQ is an acidic protein that regulates the activity of the Na+/Ca2+ exchanger in squid axon. The structure is a flattened barrel composed of two orthogonal β-sheets delimiting an inner cavity and a domain of two α-helix segments arranged as a hairpin. FTIR and CD spectroscopy showed that the interactions with several anionic lipids in the form of small unilamellar vesicles (SUVs) induced an increase in the proportion of helix secondary structure. Lower amount or no increase in α-helix was observed upon the interaction with anionic lipids in the form of large unilamellar vesicles (LUVs). The exception was 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) that was equally efficien to to induce the conformational change both in SUVs and in LUVs. In solution, the infrared spectra of ReP1-NCXSQ at temperatures above the unfolding displayed a band at 1617 cm−1 characteristic of aggregated strands. This band was not observed when the protein interacted with DMPG, indicating inhibition of aggregation in the interface. Similarly to the observed in L-BABP, another member of the fatty acid binding proteins, a conformational change in ReP1-NCXSQ was coupled to the gel to liquid-crystalline lipid phase transition.
KeywordsReP1-NCXSQ Lipid membrane Protein conformational change Infrared spectroscopy Circular dichroism Membrane curvature
Regulatory protein of the squid nerve sodium calcium exchanger
Fatty acid-binding protein
Chicken liver bile acid-binding protein
Large unilamellar vesicle
Fourier transform infrared
We thank Dr. G. Berberián and Dr. L. Beaugé for the kind donation of cDNA for ReP1-NCXSQ. This work was supported by Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Agencia Nacional de Promoción Científica y Tecnológica, AMPCyT, and Secretaría de Ciencia y Técnica-UNC, SECyT-UNC. CONICET also granted fellowships for VVG and SRS.
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