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Molecular Dynamics of Surfactant Protein C: From Single Molecule to Heptameric Aggregates

Eunice Ramírez ^*, Alberto Santana ^*, Anthony Cruz ^*, Inés Plasencia  and Gustavo E. López ^*

^* Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681; and MEMPHYS, Center for Biomembrane Physics, Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark

Correspondence: Address reprint requests to Gustavo E. López, Dept. of Chemistry, University of Puerto Rico, PO Box 9019, Mayagüez, PR 00681. Tel.: 787-265-5458; E-mail: eramirez{at}uprm.edu.

Surfactant protein C (SP-C) is a membrane-associated protein essential for normal respiration. It has been found that the -helix form of SP-C can undergo, under certain conditions, a transformation from an -helix to a ß-strand conformation that closely resembles amyloid fibrils, which are possible contributors to the pathogenesis of pulmonary alveolar proteinosis. Molecular dynamics simulations using the NAMD2 package were performed for systems containing from one to seven SP-C molecules to study their behavior in water. The results of our simulations show that unfolding of the protein occurs at the amino terminal, and despite this unfolding, no transition from -helix to ß-strand was observed.