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Rabbit sex hormone binding globulin: primary structure, tissue expression, and structure/function analyses by
The Journal of Endocrinology
|June 1, 1997
Summary
Researchers identified the rabbit sex hormone-binding globulin (SHBG) gene and expressed its protein in E. coli. Rabbit SHBG binds steroids differently than human SHBG, with the N-terminal half determining binding specificity.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Sex hormone-binding globulin (SHBG) is a key plasma protein regulating sex steroid bioavailability.
- SHBG shares structural and functional identity with androgen-binding protein (ABP) in the male reproductive tract.
Purpose of the Study:
- To isolate and characterize the rabbit SHBG cDNA.
- To investigate the steroid-binding properties of rabbit SHBG and compare them to human SHBG.
- To identify the regions of SHBG responsible for species-specific steroid-binding characteristics.
Main Methods:
- Isolation of rabbit SHBG cDNA and expression in E. coli.
- Northern blot and hot-nested PCR for mRNA analysis.
- Construction and expression of chimeric SHBG proteins.
Main Results:
- Rabbit SHBG cDNA encodes a 367-amino acid protein with significant homology to human, rat, and mouse SHBG.
- Expressed rabbit SHBG binds 5 alpha-dihydrotestosterone (DHT) but exhibits lower affinity and complex stability compared to human SHBG.
- Rabbit SHBG does not bind estradiol with high affinity, unlike human SHBG.
- Chimeric protein analysis indicated the N-terminal half of SHBG contains the steroid-binding domain, while the C-terminal half contributes to structural stability.
Conclusions:
- The N-terminal region of SHBG is crucial for steroid-binding affinity and specificity.
- The C-terminal region of SHBG plays a role in maintaining the structural integrity of the steroid-binding site.
- Understanding these species differences aids in elucidating SHBG function and steroid hormone regulation.