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Immunomagnetic capture of lens membrane fractions containing steroid binding protein
Patricia S Sexton1, Richard J Cenedella
1Department of Biochemistry, Kirksville College of Osteopathic Medicine, 800 West Jefferson, Kirksville, MO 63501, USA.
Abstract:
This study describes the use of magnetic Dynabeads to purify microsomes from a crude microsomal fraction. A 28 kDa membrane-associated protein is proposed to mediate the binding of progesterone and other steroid hormones to ocular lens membranes and the rapid-nongenomic actions of these steroids. The subcellular location of this membrane steroid binding protein (MSBP) was probed by capture of organelles containing MSBP by magnetic beads displaying an antibody to a cytoplasmic domain of the protein. The beads were exposed to a crude microsomal fraction from lens epithelia. Western blotting was used to identify captured organelles and confirm the presence of MSBP. Microsomes and trace fiber cell plasma membrane were captured. Microsomes contained the 28 kDa MSBP. Lens fiber cell membrane contained a 55 kDa immunoreactive protein. The role of this serendipitously recognized protein in binding of steroids is unknown.
Insights
Researchers used magnetic beads to isolate microsomes, identifying a 28 kDa protein that binds steroid hormones in ocular lens membranes. This protein may mediate rapid, non-genomic steroid actions.
Area of Science:
- Biochemistry
- Cell Biology
- Ophthalmology
Background:
- Steroid hormones exert rapid, non-genomic effects in various tissues, including the ocular lens.
- A putative membrane steroid binding protein (MSBP) of 28 kDa has been proposed to mediate these actions.
- Understanding the subcellular localization of MSBP is crucial for elucidating its function.
Purpose of the Study:
- To determine the subcellular location of the 28 kDa membrane-associated protein (MSBP) in ocular lens cells.
- To investigate the association of MSBP with specific cellular fractions, particularly microsomes.
Main Methods:
- Utilized magnetic Dynabeads coated with an antibody against a cytoplasmic domain of MSBP.
- Exposed magnetic beads to a crude microsomal fraction derived from ocular lens epithelia.
- Employed Western blotting to identify captured organelles and confirm the presence and size of MSBP.
Main Results:
- Magnetic beads successfully captured microsomes containing the 28 kDa MSBP.
- A small amount of lens fiber cell plasma membrane was also captured, containing a distinct 55 kDa immunoreactive protein.
- Microsomes were confirmed as a primary location for the 28 kDa MSBP.
Conclusions:
- The 28 kDa MSBP is localized to microsomes within ocular lens epithelial cells.
- Microsomes are implicated as a key cellular compartment for steroid hormone binding and rapid non-genomic signaling in the eye.
- The function of the 55 kDa protein found in the lens fiber cell membrane remains to be determined.