Ranaspumin-2: structure and function of a surfactant protein from the foam nests of a tropical frog

MacKenzie, C.D., Smith, B.O., Meister, A., Blume, A., Zhao, X., Lu, J.R., Kennedy, M.W. and Cooper, A. (2009) Ranaspumin-2: structure and function of a surfactant protein from the foam nests of a tropical frog. Biophysical Journal, 96(12), pp. 4984-4992. (doi:10.1016/j.bpj.2009.03.044)

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Abstract

Ranaspumin-2 (Rsn-2) is a monomeric, 11 kDa surfactant protein identified as one of the major foam nest components of the tĂșngara frog (Engystomops pustulosus), with an amino acid sequence unlike any other protein described so far. We report here on its structure in solution as determined by high-resolution NMR analysis, together with investigations of its conformation and packing at the air-water interface using a combination of infrared and neutron reflectivity techniques. Despite the lack of any significant sequence similarity, Rsn-2 in solution adopts a compact globular fold characteristic of the cystatin family, comprising a single helix over a four-stranded sheet, in a motif not previously associated with surfactant activity. The NMR structure of Rsn-2 shows no obvious amphiphilicity that might be anticipated for a surfactant protein. This suggests that it must undergo a significant conformational change when incorporated into the air-water interface that may involve a hinge-bending, clamshell opening of the separate helix and sheet segments to expose hydrophobic faces to air while maintaining the highly polar surfaces in contact with the underlying water layer. This model is supported by direct observation of the relative orientations of secondary structure elements at the interface by infrared reflection absorption spectroscopy, and by protein packing densities determined from neutron reflectivity profiles

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kennedy, Professor Malcolm and Cooper, Professor Alan and Smith, Dr Brian
Authors: MacKenzie, C.D., Smith, B.O., Meister, A., Blume, A., Zhao, X., Lu, J.R., Kennedy, M.W., and Cooper, A.
Subjects:Q Science > QH Natural history > QH345 Biochemistry
Q Science > QH Natural history > QH301 Biology
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
College of Science and Engineering > School of Chemistry
College of Medical Veterinary and Life Sciences > School of Life Sciences
Journal Name:Biophysical Journal
Journal Abbr.:Biophys J
ISSN:0006-3495
Published Online:10 June 2009

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