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

PLoS One. 2012;7(10):e47789. doi: 10.1371/journal.pone.0047789. Epub 2012 Oct 18.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Amino Acid Sequence
  • Animals
  • Antibodies / chemistry
  • Autopsy
  • Escherichia coli
  • Eyelids / chemistry
  • Female
  • Gene Expression
  • Humans
  • Kidney / chemistry
  • Lung / chemistry
  • Male
  • Middle Aged
  • Molecular Dynamics Simulation
  • Molecular Sequence Data
  • Organ Specificity
  • Phospholipids / chemistry
  • Protein Processing, Post-Translational*
  • Pulmonary Surfactant-Associated Protein A / chemistry*
  • Pulmonary Surfactant-Associated Protein A / genetics
  • Pulmonary Surfactant-Associated Protein A / metabolism*
  • Rabbits
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Surface Tension
  • Testis / chemistry


  • Antibodies
  • Phospholipids
  • Pulmonary Surfactant-Associated Protein A
  • Recombinant Proteins

Grant support

This research was supported by the Deutsche Forschungsgemeinschaft (DFG, http://www.dfg.de/index.jsp)given to W.B. (grant: BR 1329/12-1) and L.B. (grant BR 3681/2-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.