Studies of the structure of lung surfactant protein SP-A.
SP-A, a glycoprotein of pulmonary surfactant, consists of an NH2-terminal domain containing a collagen-like sequence and a COOH-terminal domain with sequence homology to several Ca2(+)-dependent lectins. We have compared the size, thermal stability, and secondary structure of recombinant SP-A, the product of a fibroblast line transfected with a single human gene encoding SP-A, with natural SP-A isolated from canine and human lungs. Our results suggest both recombinant and natural SP-A are assembled as large oligomers. More variability in the degree of oligomerization was observed with recombinant human SP-A than with natural canine SP-A. As shown by collagenase digestion, the full assembly of protein subunits was dependent on an intact collagen-like domain. The cysteines in the noncollagen domain of SP-A form intrachain bonds between residues 135-226 and 204-218. The circular dichroism spectra of both recombinant and natural SP-A were consistent with the presence of a collagen-like triple helix. As determined by the change in ellipticity at 205 nm, the thermal transition temperatures of canine, natural human, and recombinant SP-A were 51.5, 52.3, and 42.0 degrees C, respectively. These results suggest differences in the assembly and stability of the natural and recombinant proteins.
Haagsman
H P
HP
Department of Pediatrics, University of California, San Francisco 94143.
White
R T
RT
Schilling
J
J
Lau
K
K
Benson
B J
BJ
Golden
J
J
Hawgood
S
S
Clements
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D004220:Disulfides / Q000032:analysis; D004285:Dogs; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005796:Genes; D006023:Glycoproteins / Q000302:isolation & purification*; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000302:isolation & purification; D011487:Protein Conformation; D011510:Proteolipids / Q000235:genetics / Q000302:isolation & purification*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000235:genetics / Q000302:isolation & purification*; D011994:Recombinant Proteins / Q000302:isolation & purification
D004220:Disulfides; D006023:Glycoproteins; D010446:Peptide Fragments; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011994:Recombinant Proteins