Disease relevance of SP-B

• CONCLUSION: The surprising decrease in SP-A and SP-B mRNA levels, which contrasts with other studies, suggests intermittent asphyxial episodes impact differently on surfactant apoprotein mRNA expression than does prolonged hypoxia [1].

High impact information on SP-B

• Aggregation of dipalmitoylphosphatidylcholine (DPPC) vesicles either with or without SP-B and/or SP-C strongly depended on pH, being progressively decreased as the pH was reduced and markedly increased when pH was shifted back to 7 [2].
• Pulmonary surfactant protein A (SP-A) is synthesized by type II cells and stored intracellularly in secretory granules (lamellar bodies) together with surfactant lipids and hydrophobic surfactant proteins B and C (SP-B and SP-C) [2].
• The precursor of pulmonary surfactant-associated protein, SP-B, is composed of an NH2-terminal domain of 30 residues (a-type domain) and three tandem repeats of about 90 residues (b-type domain); biophysically active mature SP-B corresponds to the second b-type repeat [3].
• Despite their enrichment in DPPC Survanta and Exosurf exhibited poor surface activity because of low or absent SP-B/C [4].
• Intrinsic structural and functional determinants within the amino acid sequence of mature pulmonary surfactant protein SP-B [5].

Biological context of SP-B

• Pulmonary surfactant protein SP-B is absolutely required for proper function of surfactant in the alveoli, and is an important component of therapeutical surfactant preparations used to treat respiratory pathologies [5].
• Notably, one of the three intrachain bonds common to all SP-B molecules is analogous to one of the disulfide linkages in the kringle structure of complex serine proteases [6].
• With respect to the surfactant system, NO inhalation worsened the surfactant adsorption rate to an air-liquid interface and affected levels of hydrophobic surfactant proteins (SPs), SP-B and SP-C, and phospholipids, which decreased in large surfactant aggregates but not in small surfactant aggregates [7].
• Parallax experiments, as well as resonance energy transfer from SP-B tryptophan to an acceptor probe located in the center of the bilayer, indicate that there are significant differences in the extent of insertion of the protein, depending on the method of reconstitution [8].
• We conclude that there are specialized cells in the ET epithelium expressing and secreting SP-B and propose that SP-B may facilitate normal opening of the tube and mucociliary transport [9].

Anatomical context of SP-B

• The effects of surfactant protein B (SP-B) and SP-C on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages were studied both in vivo and in vitro [10].
• Pulmonary surfactant-associated protein B (SP-B) has been incorporated into vesicles of dipalmitoyl phosphatidylcholine (DPPC) or egg yolk phosphatidylcholine (PC) by two different procedures to characterize the dependence of lipid-protein interactions on the method of reconstitution [11].
• SP-B tryptophan was found to be located 10-13 A from the center of bilayers, which is consistent with a superficial location of SP-B in phosphatidylcholine membranes [8].
• With Northern blot analysis, RT-PCR, and in situ hybridizations, SP-B mRNA was identified and localized in the ET epithelium [9].
• We conclude that a surfactant composed primarily of dipalmitoylphosphatidylcholine and SP-B is adequate to maintain patency of the air capillaries of the bird lung [12].

Associations of SP-B with chemical compounds

• SP-Br had, however, effects similar to those of native SP-B on the thermotropic properties of dipalmitoylphosphatidylcholine (DPPC) bilayers [5].
• Reduced SP-Br exhibited higher structural flexibility than native SP-B, as indicated by a higher susceptibility of fluorescence emission to quenching by acrylamide and biphasic behavior during interaction of the protein with lipid bilayers and monolayers [5].
• The domain organizations of the latter proteins, however, differ from that of SP-B precursor inasmuch as they contain four tandem copies of the b-type domain and a-type domains are present both in the NH2-terminal and COOH-terminal parts of the proteins [3].
• We compared the effects of KL-4-Surfactant, an artificial preparation containing a synthetic 21 amino acid peptide with SP-B-like activity, with Exosurf, an artificial protein-free surfactant, and Survanta, a bovine protein-containing surfactant, in a saline lung lavage model of ARDS in neonatal piglets [13].
• Porcine pulmonary surfactant-associated protein SP-B was incorporated into bilayers of chain-perdeuterated dipalmitoylphosphatidylglycerol (DPPG-d62) and into bilayers containing 70 mol % dipalmitoylphosphatidylcholine (DPPC) and 30 mol % DPPG-d62 or 70 mol % chain-perdeuterated DPPC (DPPC-d62) and 30 mol % DPPG [14].

Other interactions of SP-B

• This study investigated the effect of cholesterol on the way in which hydrophobic SP-B and SP-C modulated the adsorption of lipid into the air-water interface and their respreading from collapsed phase produced on overcompression of the surface film [15].
• SP-B and the kringle of coagulation factor XII exhibit 26% residue identity [6].
• An amphipathic helical motif common to tumourolytic polypeptide NK-lysin and pulmonary surfactant polypeptide SP-B [16].

Analytical, diagnostic and therapeutic context of SP-B

• We also found that both neutral and acidic vesicles either with or without SP-B or SP-C bound to SP-A at acidic pH as demonstrated by co-migration during centrifugation [2].
• Electron microscopy showed that the injection of SP-B into an aqueous phase containing PC or DPPC vesicles (method A) induced a rapid aggregation of vesicles [11].
• In conclusion, this HPLC method affords a sensitive means of assessing modifications and conformations of SP-B or SP-C in different disease states and before functional studies [17].
• The different "squeeze-out" structures of SP-B were visualized by scanning probe microscopy and compared with structures formed by SP-C [18].
• Matrix-assisted laser desorption/ionization (MALDI) spectroscopy of R-SP-B and F-SP-C indicated that the proteins were intact and labeled with the appropriate fluorescent probe [19].

References