Cation-mediated conformational variants of surfactant protein A

BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE

卷:1453

Article

Ridsdale, RA ; Palaniyar, N ; Holterman, CE ; Inchley, K ; Possmayer, F ; Harauz, G

关键词: pulmonary surfactant;    surfactant protein A;    surfactant protein A structure;    calcium;    cation;   

DOI  :  10.1016/S0925-4439(98)00057-X

来源: Elsevier

【 摘 要 】

Surfactant protein A (SP-A) is the major protein of pulmonary surfactant. This protein is implicated in regulating surfactant secretion, alveolar processing, recycling, and in non-serum-induced immune response. An increasing body of work indicates the importance of cations, particularly calcium, on SP-A function. However, little information exists on the effects of cations on SP-A quaternary structure. Here, the quaternary organisation of bovine surfactant protein A in the presence of cations has been quantitatively and systematically studied by transmission electron microscopy. The conformation of SP-A is altered by the presence of cations, especially calcium, then sodium, and to a small extent, magnesium. There is a transition concentration, unique for each cation, at which a conformational switch occurs. These transition concentrations are. 5 mM for CaCl2, 100 mM for NaCl and 1 mM for MgCl2. Below these concentrations, SP-A exists primarily in an opened form with a large head diameter of 20 nm; above it, SP-A is mostly in a closed form due to a compaction of the headgroups resulting in a head diameter of 11 nm. There is a corresponding increase in particle length from 17 nm for opened SP-A to 20 nm for closed SP-A. The fact that the transition concentrations are within physiological range suggests that cation-mediated conformational changes of SP-A could be operative in vivo. (C) 1999 Elsevier Science B.V. All rights reserved.

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