Effect of cysteine 85 on biochemical properties and biological function of human surfactant protein A variants.
Four "core" amino acid differences within the collagen-like domain distinguish the human surfactant protein A1 (SP-A1) variants from the SP-A2 variants. One of these, cysteine 85 that could form intermolecular disulfide bonds, is present in SP-A1 (Cys85) and absent in SP-A2 (Arg85). We hypothesized that residue 85 affects both the structure and function of SP-A1 and SP-A2 variants. To test this, wild-type (WT) variants, 6A2 of SP-A1 and 1A0 of SP-A2, and their mutants (6A2(C85R) and 1A0(R85C)) were generated and studied. We found the following: (1) Residue 85 affected the binding ability to mannose and the oligomerization pattern of SP-As. The 1A0(R85C) and 6A2(C85R) patterns were similar and/or resembled those of WT 6A2 and 1A0, respectively. (2) Both SP-A WT and mutants differentially induced rough LPS and Pseudomonas aeruginosa aggregation in the following order: 1A0 > 6A2 > 6A2(C85R) > 1A0(R85C) for Re-LPS aggregation and 1A0 > 6A2 = 6A2(C85R) = 1A0(R85C) for bacterial aggregation. (3) SP-A WT and mutants enhanced phagocytosis of P. aeruginosa by rat alveolar macrophages. Their phagocytic index order was 6A2(C85R) > 1A0 > 6A2 = 1A0(R85C). The activity of mutant 1A0(C85R) was significantly lower than WT 1A0 but similar to 6A2. Compared to WT 6A2, the 6A2(C85R) mutant exhibited a significantly higher activity. These results indicate that the SP-A variant/mutant with Arg85 exhibits a higher ability to enhance bacterial phagocytosis than that with Cys85. Residue 85 plays an important role in the structure and function of SP-A and is a major factor for the differences between SP-A1 and SP-A2 variants.
Wang
Guirong
G
Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Myers
Catherine
C
Mikerov
Anatoly
A
Floros
Joanna
J
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003545:Cysteine / Q000737:chemistry* / Q000235:genetics; D006031:Glycosylation; D006801:Humans; D008070:Lipopolysaccharides / Q000737:chemistry; D016676:Macrophages, Alveolar / Q000276:immunology / Q000382:microbiology; D008969:Molecular Sequence Data; D009154:Mutation; D010587:Phagocytosis; D011550:Pseudomonas aeruginosa / Q000502:physiology; D037662:Pulmonary Surfactant-Associated Protein A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051381:Rats
D008070:Lipopolysaccharides; D037662:Pulmonary Surfactant-Associated Protein A; C445842:SFTPA1 protein, human; C445843:SFTPA2 protein, human; D003545:Cysteine