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The structure of latherin, a surfactant allergen protein from horse sweat and saliva.

Vance SJ, McDonald RE, Cooper A, Smith BO, Kennedy MW - J R Soc Interface (2013)

Bottom Line: Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation.Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported.Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.

ABSTRACT
Latherin is a highly surface-active allergen protein found in the sweat and saliva of horses and other equids. Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation. Latherin probably functions as a wetting agent in evaporative cooling in horses, but it may also assist in mastication of fibrous food as well as inhibition of microbial biofilms. It is a member of the PLUNC family of proteins abundant in the oral cavity and saliva of mammals, one of which has also been shown to be a surfactant and capable of disrupting microbial biofilms. How these proteins work as surfactants while remaining soluble and cell membrane-compatible is not known. Nor have their structures previously been reported. We have used protein nuclear magnetic resonance spectroscopy to determine the conformation and dynamics of latherin in aqueous solution. The protein is a monomer in solution with a slightly curved cylindrical structure exhibiting a 'super-roll' motif comprising a four-stranded anti-parallel β-sheet and two opposing α-helices which twist along the long axis of the cylinder. One end of the molecule has prominent, flexible loops that contain a number of apolar amino acid side chains. This, together with previous biophysical observations, leads us to a plausible mechanism for surfactant activity in which the molecule is first localized to the non-polar interface via these loops, and then unfolds and flattens to expose its hydrophobic interior to the air or non-polar surface. Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported. Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far.

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The solution structure of latherin. (a) The ensemble of the 20 latherin models (superimposed) that best fit the experimental data, shown in peptide backbone representation, shaded from blue (N-terminus) to red (C-terminus). (b) Ribbon model of the representative structure of latherin in solution illustrating secondary structure elements; α-helices are coloured red and β-strands yellow. (c) Surface contact potential (blue, positive; red, negative) of latherin mapped on the solvent accessible surface of the protein in the same orientation as (a), and (d) rotated 180°. Images and contact potential generated using PyMOL [46].
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RSIF20130453F1: The solution structure of latherin. (a) The ensemble of the 20 latherin models (superimposed) that best fit the experimental data, shown in peptide backbone representation, shaded from blue (N-terminus) to red (C-terminus). (b) Ribbon model of the representative structure of latherin in solution illustrating secondary structure elements; α-helices are coloured red and β-strands yellow. (c) Surface contact potential (blue, positive; red, negative) of latherin mapped on the solvent accessible surface of the protein in the same orientation as (a), and (d) rotated 180°. Images and contact potential generated using PyMOL [46].

Mentions: Purified recombinant latherin, which has previously been found to exhibit properties in solution similar to the natural material [3,7], exhibited sufficiently sharp, well-resolved NMR spectra suitable for high-resolution structure determination after appropriate isotopic (13C, 15N) enrichment. Potential difficulties due to spectral overlap arising from the high proportion of leucine residues were overcome as described in §2 and [27]. A total of 6922 NOE-derived distance restraints were used to calculate the structure of latherin, of which 4293 were unambiguous or manually assigned, with 2210 ambiguous restraints in the final refinement (table 1). These were supplemented by 88 RDC restraints and 34 hydrogen bond restraints. The structure calculations converged well to give good agreement with the experimental data and a tightly defined ensemble of structures (see the electronic supplementary material, tables S1 and S2; figure 1a).Table 1.


The structure of latherin, a surfactant allergen protein from horse sweat and saliva.

Vance SJ, McDonald RE, Cooper A, Smith BO, Kennedy MW - J R Soc Interface (2013)

The solution structure of latherin. (a) The ensemble of the 20 latherin models (superimposed) that best fit the experimental data, shown in peptide backbone representation, shaded from blue (N-terminus) to red (C-terminus). (b) Ribbon model of the representative structure of latherin in solution illustrating secondary structure elements; α-helices are coloured red and β-strands yellow. (c) Surface contact potential (blue, positive; red, negative) of latherin mapped on the solvent accessible surface of the protein in the same orientation as (a), and (d) rotated 180°. Images and contact potential generated using PyMOL [46].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043175&req=5

RSIF20130453F1: The solution structure of latherin. (a) The ensemble of the 20 latherin models (superimposed) that best fit the experimental data, shown in peptide backbone representation, shaded from blue (N-terminus) to red (C-terminus). (b) Ribbon model of the representative structure of latherin in solution illustrating secondary structure elements; α-helices are coloured red and β-strands yellow. (c) Surface contact potential (blue, positive; red, negative) of latherin mapped on the solvent accessible surface of the protein in the same orientation as (a), and (d) rotated 180°. Images and contact potential generated using PyMOL [46].
Mentions: Purified recombinant latherin, which has previously been found to exhibit properties in solution similar to the natural material [3,7], exhibited sufficiently sharp, well-resolved NMR spectra suitable for high-resolution structure determination after appropriate isotopic (13C, 15N) enrichment. Potential difficulties due to spectral overlap arising from the high proportion of leucine residues were overcome as described in §2 and [27]. A total of 6922 NOE-derived distance restraints were used to calculate the structure of latherin, of which 4293 were unambiguous or manually assigned, with 2210 ambiguous restraints in the final refinement (table 1). These were supplemented by 88 RDC restraints and 34 hydrogen bond restraints. The structure calculations converged well to give good agreement with the experimental data and a tightly defined ensemble of structures (see the electronic supplementary material, tables S1 and S2; figure 1a).Table 1.

Bottom Line: Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation.Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported.Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.

ABSTRACT
Latherin is a highly surface-active allergen protein found in the sweat and saliva of horses and other equids. Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation. Latherin probably functions as a wetting agent in evaporative cooling in horses, but it may also assist in mastication of fibrous food as well as inhibition of microbial biofilms. It is a member of the PLUNC family of proteins abundant in the oral cavity and saliva of mammals, one of which has also been shown to be a surfactant and capable of disrupting microbial biofilms. How these proteins work as surfactants while remaining soluble and cell membrane-compatible is not known. Nor have their structures previously been reported. We have used protein nuclear magnetic resonance spectroscopy to determine the conformation and dynamics of latherin in aqueous solution. The protein is a monomer in solution with a slightly curved cylindrical structure exhibiting a 'super-roll' motif comprising a four-stranded anti-parallel β-sheet and two opposing α-helices which twist along the long axis of the cylinder. One end of the molecule has prominent, flexible loops that contain a number of apolar amino acid side chains. This, together with previous biophysical observations, leads us to a plausible mechanism for surfactant activity in which the molecule is first localized to the non-polar interface via these loops, and then unfolds and flattens to expose its hydrophobic interior to the air or non-polar surface. Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported. Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far.

Show MeSH
Related in: MedlinePlus