Title

Interactions of The Low Molecular Weight Group of Surfactant-associated Proteins (sp 5–18) With Pulmonary Surfactant Lipids

ORCiD

Nejat Düzgüneş: 0000-0001-6159-1391

Document Type

Article

Publication Title

Biochemistry

ISSN

0006-2960

Volume

27

Issue

8

DOI

10.1021/bi00408a008

First Page

2689

Last Page

2695

Publication Date

4-1-1988

Abstract

The interaction of the low molecular weight group of surfactant-associated proteins, SP 5–18, with the major phospholipids of pulmonary surfactant was studied by fluorescence measurements of liposomal permeability and fusion, morphological studies, and surface activity measurements. The ability of SP 5–18 to increase the permeability of large unilamellar lipid vesicles was enhanced by the presence of negatively charged phospholipid. The permeability of these vesicles increased as the protein concentration was raised and the pH was lowered. SP 5–18 also induced leakage from liposomes made both from a synthetic surfactant lipid mixture and from lipids separated from SP 5–18 during its purification from canine sources. When SP 5–18 was added to egg phosphatidylglycerol liposomes, the population of liposomes which became permeable leaked all encapsulated contents, while the remaining liposomes did not leak at all. The extent of leakage was higher in the presence of 3 mM calcium. SP 5–18 also induced lipid mixing between two populations of egg phosphatidylglycerol liposomes in the presence of 3 mM calcium, as monitored by resonance energy transfer between two different fluorescent lipid probes, N-(7-nitro-2,l,3-benzoxadiazol-4-yl)phosphatidylethanolamine and N-(lissamine rhodamine B sulfonyl)phosphatidylethanolamine. Negative-staining electron microscopy showed that the addition of SP 5–18 and 3 mM calcium produced vesicles twice the size of control egg phosphatidylglycerol liposomes. In addition, surface balance measurements revealed that the adsorption of liposomal lipids to an air/water interface was enhanced by the presence of SP 5–18, negatively charged phospholipids, and 3 mM calcium. These observations suggest a similar lipid dependence for the interactions observed in the fluorescence and adsorption experiments. © 1988, American Chemical Society. All rights reserved.

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