Design of Surfactant Protein B Peptide Mimics Based on the Saposin Fold for Synthetic Lung Surfactants

Abstract

Surfactant protein (SP)-B is a 79-residue polypeptide crucial for the biophysical and physiological function of endogenous lung surfactant. SP-B is a member of the saposin or saposin-like proteins (SAPLIP) family of proteins that share an overall three-dimensional folding pattern based on secondary structures and disulfide connectivity and exhibit a wide diversity of biological functions. Here, we review the synthesis, molecular biophysics and activity of synthetic analogs of saposin proteins designed to mimic those interactions of the parent proteins with lipids that enhance interfacial activity. Saposin proteins generally interact with target lipids as either monomers or multimers via well-defined amphipathic helices, flexible hinge domains, and insertion sequences. Based on the known 3D-structural motif for the saposin family, we show how bioengineering techniques may be used to develop minimal peptide constructs that maintain desirable structural properties and activities in biomedical applications. One important application is the molecular design, synthesis and activity of Saposin mimics based on the SP-B structure. Synthetic lung surfactants containing active SP-B analogs may be potentially useful in treating diseases of surfactant deficiency or dysfunction including the neonatal respiratory distress syndrome and acute lung injury/acute respiratory distress syndrome.

A sulfur-free peptide mimic of surfactant protein B (B-YL) exhibits high in vitro and in vivo surface activities

“…Human SP-B is a 79 amino-acid, lipid-associating monomer (MW 8.7 kDa) found in the lung as a covalently linked homodimer. Early theoretical studies based on homology comparisons indicated that the SP-B monomer consists of 4-5 α-helices 6 10 with three intramolecular disulfide bridges (i.e., Cys-8 to Cys-77, Cys-11 to Cys-71 and Cys-35 to Cys-46) 11 , and belongs to the saposin protein superfamily 12 . The helical bundle for SP-B folds into two leaves, with one leaf having α-helices 1 (N-terminal helix), 5 (C-terminal helix) and 4 and the other composed of α-helices 2 and 3 13 14 .…”

“…Existing clinically available formulations are extracted from lung lavages or homogenates from pigs (Curosurf®) and cows (Infasurf®, Survanta®), and contain small amounts of SP-B and SP-C (<< 2% of total weight) in a lipid extract with DPPC as its main component. Based on the predicted 3D-saposin motif for SP-B, we have developed minimal SP-B constructs that have desirable structural properties and maintain high activities in animal models of surfactant deficiencies 9 10 . For example, Super Mini-B (SMB) is a 41-residue, ‘short-cut’ peptide ( Figure 1A ), based on the primary sequence, secondary structure and tertiary folding of the known sequence of native SP-B (79-residues), that mimics the high surfactant activity of its parent protein 10 14 16 .…”

“…Based on the predicted 3D-saposin motif for SP-B, we have developed minimal SP-B constructs that have desirable structural properties and maintain high activities in animal models of surfactant deficiencies 9 10 . For example, Super Mini-B (SMB) is a 41-residue, ‘short-cut’ peptide ( Figure 1A ), based on the primary sequence, secondary structure and tertiary folding of the known sequence of native SP-B (79-residues), that mimics the high surfactant activity of its parent protein 10 14 16 . SMB incorporates the N-terminal α-helix ( residues 8-25) and C-terminal α-helix ( residues 63-78) of native SP-B as a single linear peptide ( Figure 1A ), joined together with a customized turn to form a α-helix hairpin (α-helix/turn/α-helix, αtα) 17 .…”

Advances in synthetic lung surfactant protein technology

“…Cys-8 to Cys-77, Cys-11 to Cys-71 and Cys-35 to Cys-46). The helical bundle for SP-B is folded into two leaves and held together with disulfide bridges, with one leaf having α-helices 1 (N-terminal helix), 5 (C-terminal helix) and 4 and the second composed of α-helices 2 and 3 [4,5]. Using truncated synthetic peptides (e.g.…”

“…Cys-8 to Cys-77 and Cys-11 to Cys-71) to form an αhelix hairpin. Mini-B shows high surface activity in vitro and in animal models of surfactant deficiencies, which may be due to this mimic accurately reproducing the topology of the N-and C-terminal domains in the native SP-B [5]. Adding the hydrophobic N-terminal insertion sequence of SP-B (i.e.…”