“SP-G”, a Putative New Surfactant Protein – Tissue Localization and 3D Structure

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.

SFTA3, a novel protein of the lung: three-dimensional structure, characterisation and immune activation

“…The molecular dynamics (MD) simulations in the lipid environment were performed with the GROMACS program package (www.gromacs.org/). These modelling steps were performed as described in detail by RAUSCH et al [12]. …”

“…Recent publications demonstrate the role of SP-B in the activation of alveolar macrophages in the innate immune response in the lung [11]. Recently, another new surfactant protein SP-G has been identified and described [12]. SP-G has physicochemical properties similar to SP-B and SP-C.…”

The distribution of human surfactant proteins within the oral cavity and their role during infectious diseases of the gingiva

“…As described by Rausch et al and by Schicht et al, SP-G and SP-H seem to play an important role during inflammation processes and immune defense (Rausch et al, 2012;Schicht et al, 2014). As the oral cavity is exposed to a variety of intruders amongst them also pathogens, a functional and effective first barrier is necessary to sustain physiological stability of the oral cavity and its flora.…”

“…Immunohistochemical staining was performed with the polyclonal antibody against SP-G and SP-H (Rausch et al, 2012;Schicht et al, 2014). Antigen retrieval was performed by microwave pretreatment for 10 min and non-specific binding was inhibited by incubation with porcine normal serum (Dako) 1:5 in Tris-buffered saline (TBS).…”

“…So the aim of this study was to further investigate possible differences in the quantity of the SPs in healthy saliva compared to saliva from patients with pathologically altered periodontal tissues. Recent studies revealed two novel proteins belonging to the family of surfactant proteins namely SP-G and SP-H that have been detected in different tissues amongst them in human lung (Rausch et al, 2012;Schicht et al, 2014). In this context one further objective of the study was to investigate salivary glands and saliva for the possible presence of SP-G and SP-H.…”