Kell blood group protein shares a consensus sequence (H.E.X.X.H) with a large family of zinc-dependent endopeptidases. Kell has closest homology with neutral endopeptidase 24.11, endothelin converting enzyme-1 (ECE-1), and the PEX gene product that, as a group, comprise the M13 subfamily of mammalian neutral endopeptidases. The proteolytic activity of the M13 members, but not of Kell, has been previously demonstrated. A secreted form of wild-type Kell protein (s-Kell), devoid of the intracellular and transmembrane domains, was expressed in sf9 cells. As a negative control, an inactive mutant Kell protein (E582G) was expressed. As determined by N-terminal amino acid sequencing and mass spectrometry of the cleaved products, wild-type s-Kell, but not the control mutant protein, specifically cleaved big endothelin-3 (ET-3) at Trp(21)-Ile(22), yielding ET-3, and, to a much lesser extent, also cleaved big ET-1 and big ET-2 at Trp(21)-Val(22), yielding ET-1 and ET-2. Enzymatic activity was partially inhibited by phosphoramidon. s-Kell has an acidic pH optimum (pH 6.0 to 6.5). Like the recombinant protein, red blood cells of common Kell phenotype also preferentially process big ET-3, in contrast to Ko (null) cells that do not. These data demonstrate that the Kell blood group protein is a proteolytic enzyme that processes big ET-3, generating ET-3, a potent bioactive peptide with multiple biological roles.
Catalysis of the hydrolysis of internal, alpha-peptide bonds in a polypeptide chain by a mechanism in which water acts as a nucleophile, one or two metal ions hold the water molecule in place, and charged amino acid side chains are ligands for the metal ions.
The Kell blood group is a highly polymorphic system containing over 20 different antigens borne by the protein Kell, a 93-kDa type II glycoprotein that displays high sequence homology with members of the M13 family of zinc-dependent metalloproteases whose prototypical member is neprilysin. Kell K1 is an antigen expressed in 9% of the Caucasian population, characterized by a point mutation (T193M) of the Kell K2 antigen, and located within a putative N-glycosylation consensus sequence. Recently, a recombinant, non-physiological, soluble form of Kell was shown to cleave Big ET-3 to produce the mature vasoconstrictive peptide. To better characterize the enzymatic activity of the Kell protein and the possible differences introduced by antigenic point mutations affecting post-translational processing, the membrane-bound forms of the Kell K1 and Kell K2 antigens were expressed either in K562 cells, an erythroid cell line, or in HEK293 cells, a non-erythroid system, and their pharmacological profiles and enzymatic specificities toward synthetic and natural peptides were evaluated. Results presented herein reveal that the two antigens possess considerable differences in their enzymatic activities, although not in their trafficking pattern. Indeed, although both antigens are expressed at the cell surface, Kell K1 protein is shown to be inactive, whereas the Kell K2 antigen binds neprilysin inhibitory compounds such as phosphoramidon and thiorphan with high affinity, cleaves the precursors of the endothelin peptides, and inactivates members of the tachykinin family with enzymatic properties resembling those of other members of the M13 family of metalloproteases to which it belongs.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionHGNC
Eur. J. Biochem. 228, 931-934 (1995)[PubMed:7737196]
A 37-kDa protein was immunopurified from human erythrocytes as a complex with a monoclonal antibody directed against the Kell blood group protein of 93 kDa. A rabbit antibody raised against the purified complex reacted on a Western blot with the 93-kDa and 37-kDa proteins and was able to immunoprecipitate the 37-kDa component from K0 erythrocytes which express large amount of the Kx antigen, but not from erythrocytes of patients suffering from McLeod syndrome, a X-linked disorder in which the Kx antigen is lacking. Additional studies have shown that the 37-kDa protein is not glycosylated, and permitted the sequence of the 22 first N-terminal amino acids to be established. This sequence was identical to the predicted protein product of the XK gene cloned recently, which is deleted or mutated in McLeod patients [Ho, M., Chelly, J., Carter, N., Danek, A., Crocker, P. & Monaco, A. P. (1994) Cell 77, 869-880]. Our findings provide strong evidence that the 37-kDa red cell membrane protein is identical to the Kx protein produced by the XK structural gene and demonstrate that Kx and Kell proteins are two subunits expressed as a complex hold by disulfide bond(s) at the red cell surface.
The Kell blood group is a highly polymorphic system containing over 20 different antigens borne by the protein Kell, a 93-kDa type II glycoprotein that displays high sequence homology with members of the M13 family of zinc-dependent metalloproteases whose prototypical member is neprilysin. Kell K1 is an antigen expressed in 9% of the Caucasian population, characterized by a point mutation (T193M) of the Kell K2 antigen, and located within a putative N-glycosylation consensus sequence. Recently, a recombinant, non-physiological, soluble form of Kell was shown to cleave Big ET-3 to produce the mature vasoconstrictive peptide. To better characterize the enzymatic activity of the Kell protein and the possible differences introduced by antigenic point mutations affecting post-translational processing, the membrane-bound forms of the Kell K1 and Kell K2 antigens were expressed either in K562 cells, an erythroid cell line, or in HEK293 cells, a non-erythroid system, and their pharmacological profiles and enzymatic specificities toward synthetic and natural peptides were evaluated. Results presented herein reveal that the two antigens possess considerable differences in their enzymatic activities, although not in their trafficking pattern. Indeed, although both antigens are expressed at the cell surface, Kell K1 protein is shown to be inactive, whereas the Kell K2 antigen binds neprilysin inhibitory compounds such as phosphoramidon and thiorphan with high affinity, cleaves the precursors of the endothelin peptides, and inactivates members of the tachykinin family with enzymatic properties resembling those of other members of the M13 family of metalloproteases to which it belongs.
Protein belonging to the set of cell surface antigens found chiefly, but not solely, on blood cells. More than fifteen different blood group systems are recognised in humans. In most cases the antigenic determinant resides in the carbohydrate chains of membrane glycoproteins or glycolipids.
Enzyme which catalyzes hydrolysis reaction, i.e. the addition of the hydrogen and hydroxyl ions of water to a molecule with its consequent splitting into two or more simpler molecules.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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