Secretoglobins (SCGBs) are a family of small, alpha-helical,
disulfide
In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups.
In inorg ...
linked,
dimeric proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...
found only in mammals. This family was formerly known as the Uteroglobin/Clara cell 10-kDa family, after the two aliases of its founding member Uteroglobin.
Structure and function
The proteins are mostly alpha-helical, and the dimer is formed in an antiparallel way. The dimer interface features a cavity formed across the two monomers, which can accommodate small to medium sized ligands like steroids and phospholipids. The binding and release may be coupled with the redox state of the cystines, i.e. the presence of these disulfide bonds.
Many have regulatory functions.
Classification
The family was classified by sequence homology into 6 subfamilies in 2006.
The human and mouse genomes only contain the first three families, per a 2011 update. Not every family is monophyletic.
Rat prostatein (rat prostatic steroid binding protein) is a three component, tetrameric protein complex built from three lipophilin-like genes in groups 2 and 3. Some sources describe it as ''the''
ortholog
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speci ...
of lipophilin.
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Extra subfamilies
Subfamilies 4 and 6 were originally described as found in human and mice, but they are now treated as duplicates of existing groups. Subfamily 5 is found in neither to begin with.[
Subfamily 4 formerly included what is now known as group 1B and 2B as group 4A. Pairs of 1B/2B (ABP) genes are arranged head-to-head on the chromosome into "modules" that have been independently duplicated.][
Subfamily 6 was supposed to include human and rat RYD5,][ now reassigned Scgb1c1.][
]Fel d 1
Fel d 1 is a secretoglobin protein complex that, in cats, is encoded by the ''CH1'' (chain 1/Fel d 1-A) and ''CH2'' (chain 2/Fel d 1-B) genes.
Among cats, Fel d 1 is produced largely in their saliva and by the sebaceous glands located in their ...
was supposed to be put into two subfamilies: chain 1 in subfamily 4, and chain 2 in subfamily 5.[ Although it is not mentioned in the 2011 update, InterPro matches suggest that CH1 is similar to 1B and CH2 is similar to 2B. Extra computational research confirms the similarity, invalidating subfamilies 4 and 5 fully.]
References
Protein families
{{Protein-stub