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A selective interaction between OS-9 and the carboxyl-terminal tail of meprin beta
Larisa Litovchick1, Elena Friedmann, Shmuel Shaltiel
1Department of Adult Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Mayer Building 444, Boston, MA 02115, USA. larisa_litovchick@dfci.harvard.edu
Abstract:
OS-9, a protein previously uncharacterized, was shown to interact specifically with the intracellular region of the membrane proteinase meprin beta found in brush border membranes of kidney and small intestine. We have shown previously that this cytoplasmic region is indispensable for the maturation of meprin beta, which included an endoplasmic reticulum (ER)-to-Golgi translocation. We characterized OS-9 and found that it is associated with ER membranes and that it is exposed to the cytoplasm. Consistent with the kinetics of maturation of meprin beta, OS-9 associates with meprin beta only transiently, coinciding with ER-to-Golgi transport of meprin beta. The OS-9-binding site in the cytoplasmic domain of meprin beta overlaps the region essential for this transport. We characterized alternatively spliced forms of rat and mouse OS-9, and we found that only the non-spliced form of OS-9 binds to meprin beta, implicating the spliced out segment in the binding, and suggesting the possible mechanism of the regulation of OS-9 function. Taken together, our results indicated that OS-9 may be involved in the ER-to-Golgi transport of meprin beta. Ubiquitous expression of OS-9 raises the possibility that it may interact with other membrane proteins that possess the cytoplasmic moiety homologous to that of meprin beta during their ER-to-Golgi transition.
Insights
OS-9 protein binds to meprin beta during its transport from the endoplasmic reticulum to the Golgi apparatus. This interaction is transient and crucial for meprin beta maturation, suggesting OS-9
Area of Science:
- Molecular and Cellular Biology
- Protein Trafficking
- Membrane Protein Biogenesis
Background:
- Meprin beta is a membrane proteinase localized in the kidney and small intestine brush border.
- The cytoplasmic region of meprin beta is essential for its maturation, including endoplasmic reticulum (ER)-to-Golgi transport.
- OS-9 is a newly characterized protein associated with ER membranes and exposed to the cytoplasm.
Purpose of the Study:
- To characterize the interaction between OS-9 and meprin beta.
- To elucidate the role of OS-9 in the maturation and trafficking of meprin beta.
- To investigate the mechanism regulating OS-9 function and its potential broader role in protein transport.
Main Methods:
- Co-immunoprecipitation assays to detect protein interactions.
- Subcellular localization studies using cell fractionation and membrane association assays.
- Analysis of alternatively spliced OS-9 forms in rat and mouse to determine binding specificity.
Main Results:
- OS-9 specifically interacts with the intracellular domain of meprin beta.
- OS-9 associates transiently with meprin beta during ER-to-Golgi transport, with the binding site overlapping a critical transport region.
- Only the non-spliced form of OS-9 binds to meprin beta, suggesting regulation via alternative splicing.
Conclusions:
- OS-9 plays a role in the ER-to-Golgi transport of meprin beta.
- The transient interaction and binding site overlap suggest a direct involvement in facilitating meprin beta translocation.
- Ubiquitous OS-9 expression indicates potential involvement with other membrane proteins undergoing similar ER-to-Golgi transitions.