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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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Latherin backbone dynamics. The Lipari–Szabo extended model-free parameters derived from 15N relaxation measurements at 14.1 T are plotted by residue number in the three graphs. Backbone amide hydrogen–deuterium exchange rates indicated on the secondary structure schematic above, with residues undergoing fast exchange (lifetime <20 min) coloured red, medium exchange (20–480 minutes) cyan and slow exchange (>480 min) blue in the secondary structure cartoon.
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RSIF20130453F4: Latherin backbone dynamics. The Lipari–Szabo extended model-free parameters derived from 15N relaxation measurements at 14.1 T are plotted by residue number in the three graphs. Backbone amide hydrogen–deuterium exchange rates indicated on the secondary structure schematic above, with residues undergoing fast exchange (lifetime <20 min) coloured red, medium exchange (20–480 minutes) cyan and slow exchange (>480 min) blue in the secondary structure cartoon.

Mentions: Latherin's backbone dynamics were analysed using the Lipari–Szabo model free approach based on amide 15N relaxation measurements. The data were best fit with an overall correlation time of 11.3 ns and an axially symmetric diffusion tensor with a D///D⊥ ratio of 1.68 to obtain order parameters, local correlation times and exchange broadening terms (figure 4), revealing that the four β-strands show low levels of internal motion, with the exception of the residues preceding (Gln66, Thr68 and Leu70) and within the β bulge (Leu71, Gln72 and Leu73), and those preceding and following the short loop between β3 and β4 at the terminal end. The two termini are themselves dynamic, as is the nearby loop (121–125), though the other loop in this region (residues 78–82) shows relatively little internal motion. At the other end of the molecule, the loop between α4 and β1 (48–60) exhibits depressed order parameters indicating a high degree of flexibility that correlates with the poor definition of this part of the structure. The shorter loop between β2 and β3 (98–103), in contrast, displays motion on the millisecond timescale for the residues for which relaxation data can be obtained. The long loop between β4 and (143–151) could not be examined directly because of the absence of amide crosspeaks for residues in this region (although Gln143 at one end of the loop was seen to be dynamic), which may itself be evidence of a substantial degree of motion.Figure 4.


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)

Latherin backbone dynamics. The Lipari–Szabo extended model-free parameters derived from 15N relaxation measurements at 14.1 T are plotted by residue number in the three graphs. Backbone amide hydrogen–deuterium exchange rates indicated on the secondary structure schematic above, with residues undergoing fast exchange (lifetime <20 min) coloured red, medium exchange (20–480 minutes) cyan and slow exchange (>480 min) blue in the secondary structure cartoon.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSIF20130453F4: Latherin backbone dynamics. The Lipari–Szabo extended model-free parameters derived from 15N relaxation measurements at 14.1 T are plotted by residue number in the three graphs. Backbone amide hydrogen–deuterium exchange rates indicated on the secondary structure schematic above, with residues undergoing fast exchange (lifetime <20 min) coloured red, medium exchange (20–480 minutes) cyan and slow exchange (>480 min) blue in the secondary structure cartoon.
Mentions: Latherin's backbone dynamics were analysed using the Lipari–Szabo model free approach based on amide 15N relaxation measurements. The data were best fit with an overall correlation time of 11.3 ns and an axially symmetric diffusion tensor with a D///D⊥ ratio of 1.68 to obtain order parameters, local correlation times and exchange broadening terms (figure 4), revealing that the four β-strands show low levels of internal motion, with the exception of the residues preceding (Gln66, Thr68 and Leu70) and within the β bulge (Leu71, Gln72 and Leu73), and those preceding and following the short loop between β3 and β4 at the terminal end. The two termini are themselves dynamic, as is the nearby loop (121–125), though the other loop in this region (residues 78–82) shows relatively little internal motion. At the other end of the molecule, the loop between α4 and β1 (48–60) exhibits depressed order parameters indicating a high degree of flexibility that correlates with the poor definition of this part of the structure. The shorter loop between β2 and β3 (98–103), in contrast, displays motion on the millisecond timescale for the residues for which relaxation data can be obtained. The long loop between β4 and (143–151) could not be examined directly because of the absence of amide crosspeaks for residues in this region (although Gln143 at one end of the loop was seen to be dynamic), which may itself be evidence of a substantial degree of motion.Figure 4.

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