Synthesis and structural characterization of human-identical lung surfactant SP-C protein

An efficient synthesis for human-identical lung surfactant protein SP-C is described with a semi-automated solid phase synthesizer using Fmoc chemistry. Double coupling and acetic anhydride capping procedures were employed for synthetic cycles within the highly hydrophobic C-terminal domain of SP-C. Isolation of the protein was performed by mild cleavage and deprotection conditions and subsequent HPLC purification yielding a highly homogeneous protein as established by sequence determination, electrospray, plasma desorption and MALDI mass spectrometry. A general method has been employed for the preparation of Cys-palmitoylated protein by using temporary Cys(tButhio) protection, in situ deprotection with beta-mercaptoethanol and selective palmitoylation of resin-bound SP-C. The mild synthesis and isolation conditions provide SP-C with a high alpha-helical content, comparable to that of the natural SP-C, as assessed by CD spectra. Furthermore, first biophysical data indicate a surfactant activity comparable to that of the natural protein.