Surfactant protein D, also known as SP-D, is a lung surfactant protein part of the collagenous family of lectins called collectin. [5] In humans, SP-D is encoded by the SFTPD gene [6] [7] and is part of the innate immune system. [8] [9] Each SP-D subunit is composed of an N-terminal domain, a collagenous region, a nucleating neck region, and a C-terminal lectin domain. [5] [10] Three of these subunits assemble to form a homotrimer, which further assemble into a tetrameric complex. [5] [10]
Surfactant protein D has been shown to interact with DMBT1, [11] [12] and hemagglutinin of influenza A virus. [13] Post-translational modification of SP-D i.e. S-nitrosylation switches its function. [14] [15] [16]
Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water interface of alveoli, with hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
Versican is a large extracellular matrix proteoglycan that is present in a variety of human tissues. It is encoded by the VCAN gene.
Human serum albumin is the serum albumin found in human blood. It is the most abundant protein in human blood plasma; it constitutes about half of serum protein. It is produced in the liver. It is soluble in water, and it is monomeric.
Mannan-binding lectin serine protease 1 also known as mannose-associated serine protease 1 (MASP-1) is an enzyme that in humans is encoded by the MASP1 gene.
Collectins (collagen-containing C-type lectins) are a part of the innate immune system. They form a family of collagenous Ca2+-dependent defense lectins, which are found in animals. Collectins are soluble pattern recognition receptors (PRRs). Their function is to bind to oligosaccharide structure or lipids that are on the surface of microorganisms. Like other PRRs they bind pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) of oligosaccharide origin. Binding of collectins to microorganisms may trigger elimination of microorganisms by aggregation, complement activation, opsonization, activation of phagocytosis, or inhibition of microbial growth. Other functions of collectins are modulation of inflammatory, allergic responses, adaptive immune system and clearance of apoptotic cells.
Surfactant protein A is an innate immune system collectin. It is water-soluble and has collagen-like domains similar to SP-D. It is part of the innate immune system and is used to opsonize bacterial cells in the alveoli marking them for phagocytosis by alveolar macrophages. SP-A may also play a role in negative feedback limiting the secretion of pulmonary surfactant. SP-A is not required for pulmonary surfactant to function but does confer immune effects to the organism.
Surfactant protein B is an essential lipid-associated protein found in pulmonary surfactant. Without it, the lung would not be able to inflate after a deep breath out. It rearranges lipid molecules in the fluid lining the lung so that tiny air sacs in the lung, called alveoli, can more easily inflate.
Surfactant protein C (SP-C), is one of the pulmonary surfactant proteins. In humans this is encoded by the SFTPC gene.
Prostaglandin-H2 D-isomerase (PTGDS) is an enzyme that in humans is encoded by the PTGDS gene.
Protein-glutamine gamma-glutamyltransferase K is a transglutaminase enzyme that in humans is encoded by the TGM1 gene.
Deleted in malignant brain tumors 1 protein is a protein that in humans is encoded by the DMBT1 gene.
The alpha-2A adrenergic receptor, also known as ADRA2A, is an α2 adrenergic receptor, and also denotes the human gene encoding it.
Surfactant protein A1(SP-A1), also known as Pulmonary surfactant-associated protein A1(PSP-A) is a protein that in humans is encoded by the SFTPA1 gene.
Eukaryotic translation initiation factor 2 subunit 1 (eIF2α) is a protein that in humans is encoded by the EIF2S1 gene.
NK2 homeobox 1 (NKX2-1), also known as thyroid transcription factor 1 (TTF-1), is a protein which in humans is encoded by the NKX2-1 gene.
Integrin beta-6 is a protein that in humans is encoded by the ITGB6 gene. It is the β6 subunit of the integrin αvβ6. Integrins are αβ heterodimeric glycoproteins which span the cell’s membrane, integrating the outside and inside of the cell. Integrins bind to specific extracellular proteins in the extracellular matrix or on other cells and subsequently transduce signals intracellularly to affect cell behaviour. One α and one β subunit associate non-covalently to form 24 unique integrins found in mammals. While some β integrin subunits partner with multiple α subunits, β6 associates exclusively with the αv subunit. Thus, the function of ITGB6 is entirely associated with the integrin αvβ6.
Myristoylated alanine-rich C-kinase substrate is a protein that in humans is encoded by the MARCKS gene. It plays important roles in cell shape, cell motility, secretion, transmembrane transport, regulation of the cell cycle, and neural development. Recently, MARCKS has been implicated in the exocytosis of a number of vesicles and granules such as mucin and chromaffin. It is also the name of a protein family, of which MARCKS is the most studied member. They are intrinsically disordered proteins, with an acidic pH, with high proportions of alanine, glycine, proline, and glutamic acid. They are membrane-bound through a lipid anchor at the N-terminus, and a polybasic domain in the middle. They are regulated by Ca2+/calmodulin and protein kinase C. In their unphosphorylated form, they bind to actin filaments, causing them to crosslink, and sequester acidic membrane phospholipids such as PIP2.
Surfactant protein A2(SP-A2), also known as Pulmonary surfactant-associated protein A2(PSP-A2) is a protein that in humans is encoded by the SFTPA2 gene.
In molecular biology, Pulmonary surfactant protein D (SP-D) is a protein domain predominantly found in lung surfactant. This protein plays a special role; its primary task is to act as a defence protein against any pathogens that may invade the lung. It also plays a role in lubricating the lung and preventing it from collapse. It has an interesting structure as it forms a triple-helical parallel coiled coil, helps the protein to fold into a trimer.
Fibrinogen C domain containing 1(FIBCD1) is a protein that in humans is encoded by the FIBCD1 gene localized on chromosome 9q34.1 in close proximity to the genes encoding L- and M-ficolin. FIBCD1 is thought to have a role in both host defence and gut homeostasis.
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