Secretoglobin


Secretoglobins are a family of small, alpha-helical, disulfide linked, dimeric proteins 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 an 2011 update. Not every family is monophyletic.
Rat prostatein is a three component protein built from three lipophilin-like genes in groups 2 and 3.

Extra subfamilies

Subfamilies 4 through 6 are not found in human or mice, and they might as well be duplicates of existing groups.
Subfamily 6 was supposed to include rat RYD5, now reassigned Scgb1c1.
Subfamily 4 formerly included what is now known as group 1B and 2B as group 4A. Pairs of 1B/2B genes are arranged head-to-head on the chromosome into "modules" that have been independently duplicated.
Fel d 1 was supposed to be split 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, possibly invalidating subfamilies 4 and 5 as well.