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-	Coded for by the gene <i>rsn-2</i>, Ranaspumin-2 is a monomeric surfactant protein, with an atomic mass of 11kDa. Ranaspumin-2 (Rsn-2) is a monomeric, 11 kDa surfactant protein identified as one of the major foam nest components of the tungara frog (Engystomops pustulosus), with an amino acid sequence unlike any other protein described so far. Wereport 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	+	Coded for by the gene <i>rsn-2</i>, Ranaspumin2 (Rsn2) is a monomeric surfactant protein, with an atomic mass of 11kDa. It has a molecular weight of 13415.2 and comprises of 117 amino acids. In aqueous solution it adopts a tightly folded globular shape, which is uncharacteristic of surfactant proteins. In this 3D arrangement Rsn2 consists of a single helix over a four-stranded sheet, as can be seen in the image below. </p>
-	determined from neutron reflectivity profiles	+	<img src="http://farm7.static.flickr.com/6155/6167506290_3278200261_m.jpg" alt="Ribbon structure of Ranaspumin2"/>
-	MW= 13415.2 117 AAs	+	<p> <font size="1" font color="grey"> Image 1: Ribbons structure of Ranaspumin2 A: Frontal view B: 90 degree-rotation (Mackenzie, 2009) </font> </p>
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		+	This structure is highly unusual for a protein with surfactant properties, and appears to convey no significant amphiphilicity. It is therefore believed that Rsn2 undergoes a significant conformational change when at the air-water interface, in which it will expose hydrophobic groups to the air and hydrophilic groups to the water beneath </p>
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Revision as of 21:23, 20 September 2011

Ranaspumin2

Ranaspumin 2 is one of six proteins used by the tungara frog (Engystomops pustulosus, found in Central and South America) to form protein foam nests in which it deposits its eggs. Protein foams are relatively rare in biology, and in this case offer a biocompatible solution to incubation and protection from mechanical destruction, as well as anti-microbial properties.

A Tungara frog foam nest from Trinidad1

Structure

Coded for by the gene rsn-2, Ranaspumin2 (Rsn2) is a monomeric surfactant protein, with an atomic mass of 11kDa. It has a molecular weight of 13415.2 and comprises of 117 amino acids. In aqueous solution it adopts a tightly folded globular shape, which is uncharacteristic of surfactant proteins. In this 3D arrangement Rsn2 consists of a single helix over a four-stranded sheet, as can be seen in the image below.

Image 1: Ribbons structure of Ranaspumin2 A: Frontal view B: 90 degree-rotation (Mackenzie, 2009)

This structure is highly unusual for a protein with surfactant properties, and appears to convey no significant amphiphilicity. It is therefore believed that Rsn2 undergoes a significant conformational change when at the air-water interface, in which it will expose hydrophobic groups to the air and hydrophilic groups to the water beneath

Click here for Ranaspumin2 sequence

Function

The protein undergoes a conformational refolding whilst in solution, exhibiting significant surfactant properties at the air-water interface. This property makes it potentially useful when working with biofilms that form at the same phase-interface, as it is thought that it may assist in the destruction of the biofilm.