Unique crystal structure of a novel surfactant protein from the foam nest of the frog leptodactylus vastus

Breeding by releasing eggs into stable biofoams (>foam nests>) is a peculiar reproduction mode within anurans, fish, and tunicates; not much is known regarding the biochemistry or molecular mechanisms involved. Lv-ranaspumin (Lv-RSN-1) is the predominant protein from the foam nest of the frog Leptodactylus vastus. This protein shows natural surfactant activity, which is assumed to be crucial for stabilizing foam nests. We elucidated the amino acid sequence of Lv-RSN-1 by de novo sequencing with mass-spectrometry and determined the high-resolution X-ray structure of the protein. It has a unique fold mainly composed of a bundle of 11 α-helices and two small antiparallel β-strands. Lv-RSN-1 has a surface rich in hydrophilic residues and a lipophilic cavity in the region of the antiparallel β-sheet. It possesses intrinsic surface-active properties, reducing the surface tension of water from 73 to 61 mN m-1 (15 μg mL-1). Lv-RSN-1 belongs to a new class of surfactants proteins for which little has been reported regarding structure or function. Making the perfect egg: Frog eggs and sperm are matured in >foam nests> that are stabilized by the naturally occurring surfactant protein ranaspumin. We report the amino acid sequence, crystal structure (which corresponds to a novel fold), and biochemical properties of Lv-RSN-1, the uncommon ranaspumin from the frog Leptodactylus vastus. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.D.C.H. was recipient of a scholarship provided by Consehlo Nacional de Desenvolvimento Científico e Tecnológico (CNPq; Process No. 201633/2012-8). This work was financially supported by Coordenaçao de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), by CNPq and by the Austrian Science Funds (FWF) through project W901 (DK >Molecular Enzymology>, to K.G.)Peer Reviewe