Conformational mapping of the N-terminal segment of surfactant protein B in lipid using 13C-enhanced Fourier transform infrared spectroscopy.
Synthetic peptides based on the N-terminal domain of human surfactant protein B (SP-B1-25; 25 amino acid residues; NH2-FPIPLPYCWLCRALIKRIQAMIPKG) retain important lung activities of the full-length, 79-residue protein. Here, we used physical techniques to examine the secondary conformation of SP-B1-25 in aqueous, lipid and structure-promoting environments. Circular dichroism and conventional, 12C-Fourier transform infrared (FTIR) spectroscopy each indicated a predominate alpha-helical conformation for SP-B1-25 in phosphate-buffered saline, liposomes of 1-palmitoyl-2-oleoyl phosphatidylglycerol and the structure-promoting solvent hexafluoroisopropanol; FTIR spectra also showed significant beta- and random conformations for peptide in these three environments. In further experiments designed to map secondary structure to specific residues, isotope-enhanced FTIR spectroscopy was performed with 1-palmitoyl-2-oleoyl phosphatidylglycerol liposomes and a suite of SP-B1-25 peptides labeled with 13C-carbonyl groups at either single or multiple sites. Combining these 13C-enhanced FTIR results with energy minimizations and molecular simulations indicated the following model for SP-B1-25 in 1-palmitoyl-2-oleoyl phosphatidylglycerol: beta-sheet (residues 1-6), alpha-helix (residues 8-22) and random (residues 23-25) conformations. Analogous structural motifs are observed in the corresponding homologous N-terminal regions of several proteins that also share the 'saposin-like' (i.e. 5-helix bundle) folding pattern of full-length, human SP-B. In future studies, 13C-enhanced FTIR spectroscopy and energy minimizations may be of general use in defining backbone conformations at amino acid resolution, particularly for peptides or proteins in membrane environments.
Gordon
L M
LM
Department of Pediatrics, Martin Luther King, Jr./Drew University Medical Center and UCLA, Los Angeles, CA, USA.
Lee
K Y
KY
Lipp
M M
MM
Zasadzinski
J A
JA
Walther
F J
FJ
Sherman
M A
MA
Waring
A J
AJ
D002250:Carbon Radioisotopes; D002942:Circular Dichroism; D006801:Humans; D008081:Liposomes; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D010715:Phosphatidylglycerols; D011487:Protein Conformation; D011510:Proteolipids / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D020539:Sequence Analysis, Protein; D017550:Spectroscopy, Fourier Transform Infrared
D002250:Carbon Radioisotopes; D008081:Liposomes; D010446:Peptide Fragments; D010715:Phosphatidylglycerols; D011510:Proteolipids; D011663:Pulmonary Surfactants; C060037:1-palmitoyl-2-oleoylglycero-3-phosphoglycerol