Structure and properties of phospholipid-peptide monolayers containing monomeric SP-B(1-25) II. Peptide conformation by infrared spectroscopy.
The conformation and orientation of synthetic monomeric human sequence SP-B(1-25) (mSP-B(1-25)) was studied in films with phospholipids at the air-water (A/W) interface by polarization modulation infrared reflectance absorption spectroscopy (PM-IRRAS). Modified two-dimensional infrared (2D IR) correlation analysis was applied to PM-IRRAS spectra to define changes in the secondary structure and rates of reorientation of mSP-B(1-25) in the monolayer during compression. PM-IRRAS spectra and 2D IR correlation analysis showed that, in pure films, mSP-B(1-25) had a major alpha-helical conformation plus regions of beta-sheet structure. These alpha-helical regions reoriented later during film compression than beta structural regions, and became oriented normal to the A/W interface as surface pressure increased. In mixed films with 4:1 mol:mol acyl chain perdeuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DPPC-d(62):DOPG), the IR spectra of mSP-B(1-25) showed that a significant, concentration-dependent conformational change occurred when mSP-B(1-25) was incorporated into a DPPC-d(62):DOPG monolayer. At an mSP-B(1-25) concentration of 10 wt.%, the peptide assumed a predominantly beta-sheet conformation with no contribution from alpha-helical structures. At lower, more physiological peptide concentrations, 2D IR correlation analysis showed that the propensity of mSP-B(1-25) to form alpha-helical structures was increased. In phospholipid films containing 5 wt.% mSP-B(1-25), a substantial alpha-helical peptide structural component was observed, but regions of alpha and beta structure reoriented together rather than independently during compression. In films containing 1 wt.% mSP-B(1-25), peptide conformation was predominantly alpha-helical and the helical regions reoriented later during compression than the remaining beta structural components. The increased alpha-helical structure of mSP-B(1-25) demonstrated here by PM-IRRAS and 2D IR correlation analysis in monolayers of 4:1 DPPC:DOPG containing 1 wt.% (and, to a lesser extent, 5 wt.%) peptide may be relevant for the formation of the intermediate order 'dendritic' surface phase observed in similar surface films by epi-fluorescence.
Shanmukh
Saratchandra
S
Department of Chemistry, University of Georgia, Athens, GA 30602-2556, USA.
Biswas
Nilanjana
N
Waring
Alan J
AJ
Walther
Frans J
FJ
Wang
Zhendong
Z
Chang
Y
Y
Notter
Robert H
RH
Dluhy
Richard A
RA
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D008567:Membranes, Artificial; D008856:Microscopy, Fluorescence; D010455:Peptides / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D013500:Surface Tension
D008563:Membrane Lipids; D008567:Membranes, Artificial; D010455:Peptides; D010715:Phosphatidylglycerols; D010743:Phospholipids; D015060:1,2-Dipalmitoylphosphatidylcholine; C051388:1,2-dioleoyl-sn-glycero-3-phosphoglycerol