1. We compared the Ca2+ dependence of the self-aggregation of surfactant protein A (SP-A) with that of vesicle aggregation induced by SP-A. The Ca2+ concentration required for half-maximal activity of lipid aggregation was 0.74±0.29 μM (n = 4) for pig SP-A and 98±5 μM (n = 2) for dog SP-A. In contrast, the threshold concentration of Ca2+ required to induce self-association of both pig and dog SP-A was 0.5 mM. The Ca2+ concentration needed for half-maximal self-association was 2.36±0.15 mM (n = 4) and 0.70±0.06 mM (n = 2) for pig and dog SP-A respectively. 2. We also compared the effect of Ca2+ on the trypsin sensitivity of lipid-free and membrane-bound SP-A. At 1 μM Ca2+, the tryptic digestion patterns of dog and pig lipid-free SP-A were quite different. Dog SP-A was very sensitive to proteolysis, being almost completely digested by 30 min, while pig SP-A was very resistant, even after 12 h. After protein aggregation of lipid-free SP-A (at 5 mM Ca2+), the accessibility of the trypsin cleavage targets of the protein depended on the SP-A species (self-aggregated pig SP-A became more sensitive to degradation than its non-aggregated form, whereas self-aggregated dog SP-A was less susceptible). In contrast, membrane-bound SP-A, from either pig or dog, was clearly protected from trypsin degradation at both low (1 μM) or high (1 mM) Ca2+ concentrations. The protection was slightly higher at 1 mM Ca2+ when the extent of lipid/SP-A aggregates was maximal. 3. On the other hand, vesicle aggregation activity of SP-A was decreased by 30-40% by removing the oligosaccharide moiety of the protein, whereas self-aggregation was not influenced by deglycosylation. The presence of mannan (at concentrations not lower than 10 μg/μl) decreased vesicle aggregation induced by dog and pig SP-A by a mechanism that is independent of the binding of mannan to the carbohydrate-binding domain of SP-A. Self-aggregation of SP-A was not affected by the presence of sugars. 4. From these results, we conclude that: (1) the process of lipid aggregation induced by SP-A cannot be correlated with that of self-association of the protein occurring at supramillimolar concentrations of Ca2+; and (2) the N-linked carbohydrate moiety of SP-A and the ability of SP-A to bind carbohydrates are not involved in lipid aggregation.
Skip Nav Destination
Follow us on Twitter @Biochem_Journal
Article navigation
January 1996
-
Cover Image
Cover Image
- PDF Icon PDF LinkTable of Contents
Research Article|
January 15 1996
Comparison of lipid aggregation and self-aggregation activities of pulmonary surfactant-associated protein A Available to Purchase
Miguel L. F. RUANO;
Miguel L. F. RUANO
1Department of Biochemistry and Molecular Biology, Faculty of Biology, Complutense University of Madrid, 28040 Madrid, Spain
Search for other works by this author on:
Eugenio MIGUEL;
Eugenio MIGUEL
1Department of Biochemistry and Molecular Biology, Faculty of Biology, Complutense University of Madrid, 28040 Madrid, Spain
Search for other works by this author on:
Jesus PEREZ-GIL;
Jesus PEREZ-GIL
1Department of Biochemistry and Molecular Biology, Faculty of Biology, Complutense University of Madrid, 28040 Madrid, Spain
Search for other works by this author on:
Cristina CASALS
Cristina CASALS
*
*To whom correspondence should be addressed.
Search for other works by this author on:
Publisher: Portland Press Ltd
Received:
July 04 1995
Revision Received:
September 12 1995
Accepted:
September 12 1995
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1996
1996
Biochem J (1996) 313 (2): 683–689.
Article history
Received:
July 04 1995
Revision Received:
September 12 1995
Accepted:
September 12 1995
Citation
Miguel L. F. RUANO, Eugenio MIGUEL, Jesus PEREZ-GIL, Cristina CASALS; Comparison of lipid aggregation and self-aggregation activities of pulmonary surfactant-associated protein A. Biochem J 15 January 1996; 313 (2): 683–689. doi: https://doi.org/10.1042/bj3130683
Download citation file:
Sign in
Don't already have an account? Register
Sign in to your personal account
You could not be signed in. Please check your email address / username and password and try again.
Could not validate captcha. Please try again.
Biochemical Society Member Sign in
Sign InSign in via your Institution
Sign in via your InstitutionGet Access To This Article
Follow us on Twitter @Biochem_Journal
Open Access for all
We offer compliant routes for all authors from 2025. With library support, there will be no author nor reader charges in 5 journals. Check here |
![]() View past webinars > |