Pulmonary surfactant‐associated polypeptide SP‐C in lipid micelles: CD studies of intact SP‐C and NMR secondary structure determination of depalmitoyl‐SP‐C(1–17)

The 21‐residue surfactant peptide (LysLeu4)4Lys(KL4) is a transmembrane α‐helix with a mixed nonpolar/polar surface

“…FTIR spectroscopy revealed that SP-C adopts mainly an ahelical conformation with its a-helix oriented parallel to the lipid acyl chains [11,12]. These restults are supported by those obtained by NMR spectroscopy showing that SP-C in mixed organic solvents forms a very regular a-helix between positions 9 and 34 [13] which is perfectly suited to span a DPPC bilayer [14]. The small sizes of SP-B and SP-C have raised the possibility of producing bioactive analogues, for formulating synthetic peptide-containing surfactant preparations.…”

“…The helix presents a regular surface same number of residues and similar a-helical content as native SP-C [20]) and (ii) KL4 has a symmetric distribution of positively charged residues along the helix while native SP-C and SP-C/BR have basic residues exclusively at the N-terminal end of the helix. The latter may give KL4 a more static and uniform interaction with a phospholipid bilayer compared to native SP-C and SP-C/BR which both are expected to exhibit a 'mobility gradient' [14] due to greater lateral mobility in the C-terminal end than in the N-terminal end. We speculate that such effects may contribute to the observed differences in spreading kinetics between KL4 and native SP-C and SP-C/ BR.…”

“…interface Spreading kinetics of 2% (w/w) of KL4 in a DPPC/PG/PA 68:22:9 (by weight) mixture at an air/water interface was compared to that of native SP-C and SP-C/BR [20], both with transmembranous c~-helices in similar phospholipid mixtures [11,12,14,26]. KL4 is less efficient than native SP-C and SP-C/BR in accelerating the spreading of the lipid mixture and also reaches a lower surface pressure after 1 min (Fig.…”

“…KL4 does accelerate the spreading of lipids at an air/water interface but it is less effective than both native SP-C and the SP-C/BR hybrid in this respect. Perhaps the most prominent differences between KL4 on the one hand and native SP-C and SP-C/BR on the other are that (i) the KL4 helix is shorter (about 30 A, compared to 37,4, in native SP-C [13,14] and presumably also in SP-C/BR with the it is calculated that the helix axis and the all-trans lipid acyl chains make a maximum tilt from a normal to the ATR plate of 27 ° and 20 °, respectively. This means that the KL4 peptide is oriented practically parallel to the lipid acyl chains in a DPPC/PG bilayer.…”

Pulmonary surfactant‐associated polypeptide C in a mixed organic solvent transforms from a monomeric α‐helical state into insoluble β‐sheet aggregates

“…Based on the length of the a-helix of asp-C and data from infrared spectroscopy (Pastrana et al, 1991 ;Vandenbussche et al, 1992), it has been concluded that the aSP-C spans a phospholipid bilayer in vivo (Johansson et al, 1995b). It was, thus, desirable to assess cross-peaks involving the hackhone amide protons.…”