Secretoglobin
Secretoglobins (SCGBs) 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 functionThe 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.[1] The binding and release may be coupled with the redox state of the cystines, i.e. the presence of these disulfide bonds.[2] Many have regulatory functions. ClassificationThe family was classified by sequence homology into 6 subfamilies in 2006.[3] The human and mouse genomes only contain the first three families, per a 2011 update. Not every family is monophyletic.[4]
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 of lipophilin.[3] Extra subfamiliesSubfamilies 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.[3] 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.[4] Subfamily 6 was supposed to include human and rat RYD5,[3] now reassigned Scgb1c1.[4] Fel d 1 was supposed to be put into two subfamilies: chain 1 in subfamily 4, and chain 2 in subfamily 5.[3] Although it is not mentioned in the 2011 update, InterPro matches suggest that CH1 is similar to 1B and CH2 is similar to 2B.[5] Extra computational research confirms the similarity, invalidating subfamilies 4 and 5 fully.[6] References
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