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"SP-G", a putative new surfactant protein--tissue localization and 3D structure.

Rausch F, Schicht M, Paulsen F, Ngueya I, Bräuer L, Brandt W - PLoS ONE (2012)

Bottom Line: In this work, computational chemistry and molecular-biological methods were combined to localize and characterize SP-G.With the help of a protein structure model, specific antibodies were obtained which allowed the detection of SP-G not only on mRNA but also on protein level.This includes also the possibility of interactions with lipid systems and with that, a potential surface-regulatory feature of SP-G.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Halle, Germany.

ABSTRACT
Surfactant proteins (SP) are well known from human lung. These proteins assist the formation of a monolayer of surface-active phospholipids at the liquid-air interface of the alveolar lining, play a major role in lowering the surface tension of interfaces, and have functions in innate and adaptive immune defense. During recent years it became obvious that SPs are also part of other tissues and fluids such as tear fluid, gingiva, saliva, the nasolacrimal system, and kidney. Recently, a putative new surfactant protein (SFTA2 or SP-G) was identified, which has no sequence or structural identity to the already know surfactant proteins. In this work, computational chemistry and molecular-biological methods were combined to localize and characterize SP-G. With the help of a protein structure model, specific antibodies were obtained which allowed the detection of SP-G not only on mRNA but also on protein level. The localization of this protein in different human tissues, sequence based prediction tools for posttranslational modifications and molecular dynamic simulations reveal that SP-G has physicochemical properties similar to the already known surfactant proteins B and C. This includes also the possibility of interactions with lipid systems and with that, a potential surface-regulatory feature of SP-G. In conclusion, the results indicate SP-G as a new surfactant protein which represents an until now unknown surfactant protein class.

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Related in: MedlinePlus

Structure presentation of the final protein model for SP-G (top).Only the protein backbone is shown in ribbon presentation. α-helices in blue, β-sheets in red, turns and random elements in green and cyan. The same color code is used on the sequence bar (bottom).
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pone-0047789-g004: Structure presentation of the final protein model for SP-G (top).Only the protein backbone is shown in ribbon presentation. α-helices in blue, β-sheets in red, turns and random elements in green and cyan. The same color code is used on the sequence bar (bottom).

Mentions: With this, we are the first who can present a three dimensional model of the SP-G structure. The model structure (Figure 4) is dominated by an α-helix of the amino acids 42–56 and an antiparallel β-sheet structure spanning the residues 63–68 and 72–78. The hydrophobic part of the N-terminal signal peptide is modeled as a short α-helix (8–13). This helix as well as the rest of the 19 N-terminal amino acids are loosely attached to the surface and cover the hydrophobic core of the protein. The fixation on the protein is not very strong so that it could fold out at any time to interact with or get embedded into a lipid system due to its hydrophobic character. The α-helix 42–56 also contains many hydrophobic residues (seven leucines and one phenylalanine). But in addition, it contains two glutamates and one lysine which could interact with the polar head groups of lipid moieties. Furthermore, the structure model shows that the two available cysteine residues are about 10 Å apart. This drastically reduces the possibility of an intramolecular disulfide bond. However, one of the cysteines (Cys76) is located on the surface of the protein and could be able to form an intermolecular disulfide bond, which would lead to a covalently connected protein dimer. Although there is no surface region predestined for interactions with another monomer, also a non-covalent oligomerization of SP-G cannot be excluded on the basis of the protein structure model.


"SP-G", a putative new surfactant protein--tissue localization and 3D structure.

Rausch F, Schicht M, Paulsen F, Ngueya I, Bräuer L, Brandt W - PLoS ONE (2012)

Structure presentation of the final protein model for SP-G (top).Only the protein backbone is shown in ribbon presentation. α-helices in blue, β-sheets in red, turns and random elements in green and cyan. The same color code is used on the sequence bar (bottom).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3475697&req=5

pone-0047789-g004: Structure presentation of the final protein model for SP-G (top).Only the protein backbone is shown in ribbon presentation. α-helices in blue, β-sheets in red, turns and random elements in green and cyan. The same color code is used on the sequence bar (bottom).
Mentions: With this, we are the first who can present a three dimensional model of the SP-G structure. The model structure (Figure 4) is dominated by an α-helix of the amino acids 42–56 and an antiparallel β-sheet structure spanning the residues 63–68 and 72–78. The hydrophobic part of the N-terminal signal peptide is modeled as a short α-helix (8–13). This helix as well as the rest of the 19 N-terminal amino acids are loosely attached to the surface and cover the hydrophobic core of the protein. The fixation on the protein is not very strong so that it could fold out at any time to interact with or get embedded into a lipid system due to its hydrophobic character. The α-helix 42–56 also contains many hydrophobic residues (seven leucines and one phenylalanine). But in addition, it contains two glutamates and one lysine which could interact with the polar head groups of lipid moieties. Furthermore, the structure model shows that the two available cysteine residues are about 10 Å apart. This drastically reduces the possibility of an intramolecular disulfide bond. However, one of the cysteines (Cys76) is located on the surface of the protein and could be able to form an intermolecular disulfide bond, which would lead to a covalently connected protein dimer. Although there is no surface region predestined for interactions with another monomer, also a non-covalent oligomerization of SP-G cannot be excluded on the basis of the protein structure model.

Bottom Line: In this work, computational chemistry and molecular-biological methods were combined to localize and characterize SP-G.With the help of a protein structure model, specific antibodies were obtained which allowed the detection of SP-G not only on mRNA but also on protein level.This includes also the possibility of interactions with lipid systems and with that, a potential surface-regulatory feature of SP-G.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Halle, Germany.

ABSTRACT
Surfactant proteins (SP) are well known from human lung. These proteins assist the formation of a monolayer of surface-active phospholipids at the liquid-air interface of the alveolar lining, play a major role in lowering the surface tension of interfaces, and have functions in innate and adaptive immune defense. During recent years it became obvious that SPs are also part of other tissues and fluids such as tear fluid, gingiva, saliva, the nasolacrimal system, and kidney. Recently, a putative new surfactant protein (SFTA2 or SP-G) was identified, which has no sequence or structural identity to the already know surfactant proteins. In this work, computational chemistry and molecular-biological methods were combined to localize and characterize SP-G. With the help of a protein structure model, specific antibodies were obtained which allowed the detection of SP-G not only on mRNA but also on protein level. The localization of this protein in different human tissues, sequence based prediction tools for posttranslational modifications and molecular dynamic simulations reveal that SP-G has physicochemical properties similar to the already known surfactant proteins B and C. This includes also the possibility of interactions with lipid systems and with that, a potential surface-regulatory feature of SP-G. In conclusion, the results indicate SP-G as a new surfactant protein which represents an until now unknown surfactant protein class.

Show MeSH
Related in: MedlinePlus