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- 저자 : Melanie K. Bothe (검색결과 2 건)
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Melanie K. Bothe,Lars Mundhenk,Matthias Kaup,Christoph Weise,Achim D. Gruber 한국분자세포생물학회 2011 Molecules and cells Vol.32 No.6
Several members of the CLCA family of proteins, origi-nally named chloride channels, calcium-activated, have been shown to modulate chloride conductance in various cell types via an unknown mechanism. Moreover, the human (h) hCLCA1 is thought to modulate the severity of disease in asthma and cystic fibrosis (CF) patients. All CLCA proteins are post-translationally cleaved into two subunits, and recently, a conserved HEXXH zinc-binding amino acid motif has been identified, suggesting a role for CLCA proteins as metalloproteases. Here, we have characterized the cleavage and autoproteolytic activity of the murine model protein mCLCA3, which represents the murine orthologue of human hCLCA1. Using crude membrane fractions from transfected HEK293 cells, we demonstrate that mCLCA3 cleavage is zinc-dependent and exclusively inhibited by cation-chelating metalloprotease inhibitors. Cellular transport and secretion were not affected in response to a cleavage defect that was introduced by the insertion of an E157Q mutation within the HEXXH motif of mCLCA3. Interspecies conservation of these key results was further confirmed with the porcine (p) orthologue of hCLCA1 and mCLCA3, pCLCA1. Importantly, the mCLCA3E157Q mutant was cleaved after co-transfection with the wild-type mCLCA3 in HEK293 cells, suggesting that an intermolecular autoproteolytic event takes place. Edman degradation and MALDI-TOF-MS of the protein fragments identified a single cleavage site in mCLCA3 between amino acids 695 and 696. The data strongly sug-gest that secreted CLCA proteins have zinc-dependent autoproteolytic activity and that they may cleave additional proteins.
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Melanie K. Bothe,Achim D. Gruber,Lars Mundhenk,Carol L. Beck,Matthias Kaup 한국분자세포생물학회 2012 Molecules and cells Vol.33 No.3
CLCA proteins (calcium-activated chloride channel regulators) have been linked to diseases involving secretory disorders, including cystic fibrosis (CF) and asthma. They have been shown to modulate endogenous chloride conductance, possibly by acting as metalloproteases. Based on the differential processing of the subunits after post-translational cleavage, two subgroups of CLCA proteins can be distinguished. In one subgroup, both subunits are secreted, in the other group, the carboxy-terminal subunit possesses a transmembrane segment, resulting in shedding of only the amino-terminal subunit. Recent data on the post-translational cleavage and proteolytic activity of CLCA are limited to secreted CLCA. In this study, we cha-racterized the cleavage of mCLCA6, a murine CLCA pos-sessing a transmembrane segment. As for secreted CLCA, the cleavage in the endoplasmic reticulum was not observed for a protein with the E157Q mutation in the HEXXH motif of mCLCA6, suggesting that this mutant protein and secreted CLCA family members share a similar autoproteolytic cleavage mechanism. In contrast to secreted CLCA proteins with the E157Q mutation, the uncleaved precursor of the mCLCA6E157Q mutant reached the plasma membrane, where it was cleaved and the amino-terminal subunit was shed into the supernatant. Using crude membrane fractions, we showed that cleavage of the mCLCA6E157Q protein is zinc-dependent and sensitive to metalloprotease inhibitors, suggesting secondary cleavage by a metalloprotease. Interestingly, anchorage of mCLCA6E157Q to the plasma membrane is not essential for its secondary cleavage, because the mCLCA6∆TME157Q mutant still underwent cleavage. Our data suggest that the processing of CLCA proteins is more complex than previously recognized.
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