Limits...
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.

Show MeSH

Related in: MedlinePlus

The environment of the solvent exposed tryptophan. Trp87 and surrounding side chains are shown in stick representation, with side-chain oxygens and nitrogens coloured red and blue, respectively. Image created using PyMOL [46].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4043175&req=5

RSIF20130453F6: The environment of the solvent exposed tryptophan. Trp87 and surrounding side chains are shown in stick representation, with side-chain oxygens and nitrogens coloured red and blue, respectively. Image created using PyMOL [46].

Mentions: One puzzle presented by our previous work on latherin relates to the fluorescence properties of its single tryptophan residue (Trp87 in the structure; [3]). Latherin in dilute aqueous solution exhibits a relatively red-shifted Trp fluorescence emission spectrum, usually indicative of exposure to solvent water or a charged local protein environment [66,67]. Quenching of fluorescence emission by Trp87 by neutrally charged compounds (succinimide, acrylamide) was efficient, consistent with side-chain exposure to polar solvent water [3]. But, quenching by iodide (I−), normally a highly efficient quenching agent for exposed Trp residues, was unexpectedly ineffective [3]. The new structure explains this conundrum in that Trp87 is exposed on the exterior of the protein, midway down the concave side of the curved cylinder, with its indole side chain sandwiched between, and encircled by, nearby charged amino acid side chains (Asp85, Asp111, Arg113, Arg138 and Glu76; figure 6). So, Trp87 is in a position to encounter solvent water and be quenched by neutral compounds, but its local environment is sufficiently dominated by negatively charged groups to repel a normally highly efficient but negatively charged quencher.Figure 6.


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 environment of the solvent exposed tryptophan. Trp87 and surrounding side chains are shown in stick representation, with side-chain oxygens and nitrogens coloured red and blue, respectively. Image created using PyMOL [46].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSIF20130453F6: The environment of the solvent exposed tryptophan. Trp87 and surrounding side chains are shown in stick representation, with side-chain oxygens and nitrogens coloured red and blue, respectively. Image created using PyMOL [46].
Mentions: One puzzle presented by our previous work on latherin relates to the fluorescence properties of its single tryptophan residue (Trp87 in the structure; [3]). Latherin in dilute aqueous solution exhibits a relatively red-shifted Trp fluorescence emission spectrum, usually indicative of exposure to solvent water or a charged local protein environment [66,67]. Quenching of fluorescence emission by Trp87 by neutrally charged compounds (succinimide, acrylamide) was efficient, consistent with side-chain exposure to polar solvent water [3]. But, quenching by iodide (I−), normally a highly efficient quenching agent for exposed Trp residues, was unexpectedly ineffective [3]. The new structure explains this conundrum in that Trp87 is exposed on the exterior of the protein, midway down the concave side of the curved cylinder, with its indole side chain sandwiched between, and encircled by, nearby charged amino acid side chains (Asp85, Asp111, Arg113, Arg138 and Glu76; figure 6). So, Trp87 is in a position to encounter solvent water and be quenched by neutral compounds, but its local environment is sufficiently dominated by negatively charged groups to repel a normally highly efficient but negatively charged quencher.Figure 6.

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