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94  structures 46  species 5  interactions 96  sequences 8  architectures

Family: Surfac_D-trimer (PF09006)

Summary: Lung surfactant protein D coiled-coil trimerisation

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This is the Wikipedia entry entitled "Pulmonary surfactant protein D". More...

Pulmonary surfactant protein D Edit Wikipedia article

PDB 2os9 EBI.jpg
crystal structure of the trimeric neck and carbohydrate recognition domain of human surfactant protein d in complex with myoinositol
Symbol Surfac_D-trimer
Pfam PF09006
InterPro IPR015097

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.[1]


Pulmonary surfactant protein D (SP-D), has an important role in acting as a lung host defence protein. SP-D has a significant roles in immune and inflammatory regulation of the lung as it regulates of the level of surfactant in the lungs by a process named surfactant homeostasis.[2]


SP-D is a type of lectin, more specifically they are a collagen-containing C-type (calcium dependent) lectin which are named collectins. The collectins are responsible for immune and inflammatory control. They have a very basic structure,

  • triple-helical collagen region
  • C-terminal homotrimeric lectin or carbohydrate recognition domain (CRD).

SP-D is actually a monomer, these monomers assist in high affinity saccharide binding. Three of the same type of monomers associate to form a homotrimer. [3]


  1. ^ Kovacs H, O'Ddonoghue SI, Hoppe HJ, Comfort D, Reid KB, Campbell D, Nilges M (October 2002). "Solution structure of the coiled-coil trimerization domain from lung surfactant protein D". J. Biomol. NMR 24 (2): 89–102. doi:10.1023/A:1020980006628. PMID 12495025. 
  2. ^ Zhang P, McAlinden A, Li S, Schumacher T, Wang H, Hu S; et al. (2001). "The amino-terminal heptad repeats of the coiled-coil neck domain of pulmonary surfactant protein d are necessary for the assembly of trimeric subunits and dodecamers.". J Biol Chem 276 (23): 19862–70. doi:10.1074/jbc.M100597200. PMID 11279100. 
  3. ^ Kishore U, Greenhough TJ, Waters P, Shrive AK, Ghai R, Kamran MF; et al. (2006). "Surfactant proteins SP-A and SP-D: structure, function and receptors.". Mol Immunol 43 (9): 1293–315. doi:10.1016/j.molimm.2005.08.004. PMID 16213021. 

This article incorporates text from the public domain Pfam and InterPro IPR015097

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Lung surfactant protein D coiled-coil trimerisation Provide feedback

This domain, predominantly found in lung surfactant protein D, forms a triple-helical parallel coiled coil, and mediates trimerisation of the protein [1].

Literature references

  1. Kovacs H, O'Ddonoghue SI, Hoppe HJ, Comfort D, Reid KB, Campbell D, Nilges M; , J Biomol NMR. 2002;24:89-102.: Solution structure of the coiled-coil trimerization domain from lung surfactant protein D. PUBMED:12495025 EPMC:12495025

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR015097

This domain is found in the SFTPD family, which includes lung surfactant protein D (SFTPD), conglutinin, collectin-43 and collectin-46. It forms a triple-helical parallel coiled coil, and mediates trimerisation of the protein [PUBMED:12495025].

Domain organisation

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Curation and family details

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Curation View help on the curation process

Seed source: pdb_1m7l
Previous IDs: none
Type: Coiled-coil
Author: Mistry J, Sammut SJ
Number in seed: 5
Number in full: 96
Average length of the domain: 42.90 aa
Average identity of full alignment: 55 %
Average coverage of the sequence by the domain: 14.13 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 80369284 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.7 20.7
Trusted cut-off 20.8 21.3
Noise cut-off 20.5 20.6
Model length: 46
Family (HMM) version: 7
Download: download the raw HMM for this family

Species distribution

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There are 5 interactions for this family. More...

Surfac_D-trimer Collagen Lectin_C Collagen Lectin_C


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Surfac_D-trimer domain has been found. There are 94 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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