1. Elucidation of Lipid Binding Sites on Lung Surfactant Protein A Using X-ray Crystallography, Mutagenesis, and Molecular Dynamics Simulations
- Author
-
Barbara A. Seaton, Klaus Schulten, Huixing Wu, Francis X. McCormack, Michael J. Rynkiewicz, and Boon Chong Goh
- Subjects
0301 basic medicine ,1,2-Dipalmitoylphosphatidylcholine ,Protein Conformation ,Proteolipids ,Collectin ,Molecular Dynamics Simulation ,Crystallography, X-Ray ,Biochemistry ,Article ,Lipid A ,03 medical and health sciences ,chemistry.chemical_compound ,Protein structure ,Pulmonary surfactant ,Animals ,Binding site ,Binding Sites ,030102 biochemistry & molecular biology ,biology ,Pulmonary Surfactant-Associated Protein A ,Pulmonary Surfactants ,Surfactant protein A ,Rats ,030104 developmental biology ,chemistry ,Dipalmitoylphosphatidylcholine ,Mutation ,biology.protein ,Mutagenesis, Site-Directed ,lipids (amino acids, peptides, and proteins) ,Protein A - Abstract
Surfactant protein A (SP-A) is a collagenous C-type lectin (collectin) that is critical for pulmonary defense against inhaled microorganisms. Bifunctional avidity of SP-A for pathogen-associated molecular patterns (PAMPs) such as lipid A and for dipalmitoylphosphatidylcholine (DPPC), the major component of surfactant membranes lining the air-liquid interface of the lung, ensures that the protein is poised for first-line interactions with inhaled pathogens. To improve our understanding of the motifs that are required for interactions with microbes and surfactant structures, we explored the role of the tyrosine-rich binding surface on the carbohydrate recognition domain of SP-A in the interaction with DPPC and lipid A using crystallography, site-directed mutagenesis, and molecular dynamics simulations. Critical binding features for DPPC binding include a three-walled tyrosine cage that binds the choline headgroup through cation-π interactions and a positively charged cluster that binds the phosphoryl group. This basic cluster is also critical for binding of lipid A, a bacterial PAMP and target for SP-A. Molecular dynamics simulations further predict that SP-A binds lipid A more tightly than DPPC. These results suggest that the differential binding properties of SP-A favor transfer of the protein from surfactant DPPC to pathogen membranes containing appropriate lipid PAMPs to effect key host defense functions.
- Published
- 2016