Functional and Structural Characterization of Pulmonary Surfactant Protein SP-C in Nanodiscs: A Nanotechnological Approach

Abstract

Because membrane proteins need to be taken out of their natural environment and reconstituted into artificial milieus to perform structure-function studies, the search for mimetic membranes that retain their native structure and functional activity constitutes a challenge.Nanodiscs emerge as a powerful tool for achieving this goal. These discoidal particles are constituted by a phospholipid bilayer encircled by a membrane scaffold protein, which determines the size of the nanodiscs. We are focused on the study of pulmonary surfactant protein C (SP-C), a key component of the pulmonary surfactant lipoprotein complex that reduces the surface tension in the pulmonary alveoli preventing them from collapse during respiration. This transmembrane protein is a 35 amino acid peptide dually palmitoylated in its N-terminal segment. SP-C is one of the most hydrophobic proteins that are known and its low stability and the high tendency to form aggregated beta-sheets in aqueous solvents difficult its structural and functional characterization even in the presence of detergents.In the present work, nanodiscs containing both native and a non-palmitoylated recombinant version of SP-C have been obtained using POPC as a lipid membrane model. The incorporation of SP-C into nanodiscs provides a novel approach for structural and functional studies of this membrane protein in a bilayer mimetic system.