Infrared reflection-absorption of melittin interaction with phospholipid monolayers at the air/water interface.
The interaction of melittin with monolayers of 1,2-dipalmitoylphosphatidylcholine and 1,2-dipalmitoylphosphatidylserine has been investigated with infrared external reflection-absorption spectroscopy. Improved instrumentation permits determination of acyl chain conformation and peptide secondary structure in situ at the air/water interface. The IR frequency of the 1,2-dipalmitoylphosphatidylcholine antisymmetric acyl chain CH2 stretching vibration decreases by 1.3 cm-1 upon melittin insertion, consistent with acyl chain ordering, whereas the same vibrational mode increases by 0.5 cm-1 upon peptide interaction with the 1,2-dipalmitoylphosphatidylserine monolayer, indicative of chain disordering. Thus the peptide interacts quite differently with zwitterionic compared with negatively charged monolayer surfaces. Melittin in the monolayer adopted a secondary structure with an amide l(l') frequency (1635 cm-1) dramatically different from the alpha-helical motif (amide l frequency 1656 cm-1 in a dry or H2O hydrated environment, amide l' frequency 1645 cm-1 in an H-->D exchanged alpha-helix) assumed in bilayer or multibilayer environments. This work represents the first direct in situ spectroscopic indication that peptide secondary structure in lipid monolayers may differ from that in bilayers.
Flach
C R
CR
Department of Chemistry, Newark College, Rutgers University, New Jersey 07102, USA.
Prendergast
F G
FG
Mendelsohn
R
R
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000388:Air; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D008555:Melitten / Q000737:chemistry*; D008968:Molecular Conformation; D010718:Phosphatidylserines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D014867:Water
D010718:Phosphatidylserines; D010743:Phospholipids; D014867:Water; D008555:Melitten; D015060:1,2-Dipalmitoylphosphatidylcholine; C038694:dipalmitoylphosphatidylserine