Mutational analysis of Arg197 of rat surfactant protein A. His197 creates specific lipid uptake defects.
In previous studies, tandem mutagenesis of Glu195 and Arg197 of surfactant protein A (SP-A) has implicated both residues as critical participants in the interaction of the molecule with alveolar type II cells and phospholipids. We substituted Ala, Lys, His, Asp, and Asn mutations for Arg to evaluate the role of a basic amino acid at position 197 in SP-A action. Unexpectedly, Ala197 retained complete activity in the SP-A functions of carbohydrate binding, type II cell binding, inhibition of surfactant secretion, lipid binding, lipid aggregation, and lipid uptake by type II cells. The results unambiguously demonstrate that Arg197 is not mechanistically essential for SP-A function. The Lys197 mutation displayed all functions of the wild type protein but exhibited a 2-fold increase in lipid uptake activity. The His197 mutation displayed all SP-A functions studied except for lipid uptake. The results obtained with the His197 mutation clearly demonstrate that lipid aggregation alone by SP-A is insufficient to promote lipid uptake by type II cells. These findings indicate that specific interactions between type II cells and SP-A are involved in the phospholipid uptake processes.
Pattanajitvilai
S
S
The Lord and Taylor Laboratory for Lung Biochemistry, National Jewish Medical and Research Center, Denver, Colorado 80206, USA.
Kuroki
Y
Y
Tsunezawa
W
W
McCormack
F X
FX
Voelker
D R
DR
D000818:Animals; D002478:Cells, Cultured; D008055:Lipids / Q000493:pharmacokinetics*; D008081:Liposomes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D010743:Phospholipids / Q000378:metabolism; D011510:Proteolipids / Q000235:genetics* / Q000502:physiology; D011650:Pulmonary Alveoli / Q000502:physiology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000235:genetics* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D008055:Lipids; D008081:Liposomes; D010743:Phospholipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011956:Receptors, Cell Surface; C067774:surfactant protein A receptor; D013755:Tetradecanoylphorbol Acetate