Pulmonary Surfactant Protein B (SP-B): Structure-Function Relationships

TLDR

SP‑B is a pulmonary surfactant protein that prevents alveolar collapse by resisting surface tension. Synthetic 21‑residue peptides mimicking SP‑B’s hydrophobic and hydrophilic domains enhance phospholipid surface‑tension reduction and partition into the lipid bilayer, contacting both head groups and acyl chains. The activity requires intermittent positive charges, and these peptides increase inter‑ and intramolecular lipid order, thereby boosting the lateral stability of the phospholipid layer to resist surface tension.

Abstract

SP-B is a protein in pulmonary surfactant that is, in greatest part, responsible for resistance to surface tension and prevention of collapse of pulmonary alveoli. Peptides of 21 residues, synthesized following the sequence of SP-B or resembling the hydrophobic and hydrophilic domains of SP-B (such as RLLLLRLLLLRLLLLRLLLLR, R, Arg, and L, Leu), enhanced the abilities of phospholipids to reduce surface tension both in vitro and in vivo. Intermittent positively charged residues were essential for this activity. The SP-B-like peptides were found by tryptophan fluorescence to partition within the phospholipid layer in contact with both polar head groups and acyl side chains. These data, together with findings that the SP-B-related peptides increase inter- and intramolecular order of the phospholipid layer, suggest that SP-B resists surface tension by increasing lateral stability of the phospholipid layer.