Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.52 (PNGase F)
 1,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously described the production of monoclonal antibodies against a preparation of membrane glycoproteins from human brain [Berglund et al. (1987) J. Neurochem. 48, 809-815]. One of the glycoproteins, recognized by monoclonal antibody CF3, was specifically expressed in the brain. We now report the isolation and characterization of this glycoprotein, called glycoprotein 135 (Gp135). Gp135 was purified by means of lentil lectin affinity chromatography and immunoaffinity chromatography, using monoclonal antibody CF3, from a crude membrane extract of human brain cortex. Gp135 was shown to consist of a glycosylated single polypeptide chain with an apparent molecular mass of 135 kDa. The size of the polypeptide moiety was estimated to 115 kDa following N-glycanase digestion. The glycoprotein is anchored in the membrane by a glycosylphosphatidylinositol tail, as shown by phospholipase C digestion and liposome incorporation experiments. Amino acid sequence analysis of the amino terminal, and of an internal peptide obtained by V8 protease digestion of the glycoprotein, revealed a strong similarity to three previously described glycoproteins from chicken (contactin and F11) and mouse (F3) brains. These glycoproteins belong to the immunoglobulin superfamily and are implicated in cell adhesion phenomena in the developing brain. Gp135 may be the human counterpart to one or several of these glycoproteins.
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PMID:Isolation and characterization of a membrane glycoprotein from human brain with sequence similarities to cell adhesion proteins from chicken and mouse. 202 73

The mechanisms by which a stimulatory monoclonal antibody (mAb), called mAb F11, induces granular secretion and aggregation in human platelets have been characterized. Fab fragments of mAb F11, as well as an mAb directed against the platelet Fc gamma RII receptor (mAb IV.3) were found to inhibit mAb F11-induced platelet secretion and aggregation, indicating that the mAb F11 IgG molecule interacts with the Fc gamma RII receptor through its Fc domain and with its own antigen through its Fab domain. The mAb F11 recognized two platelet proteins of 32 and 35 kDa on the platelet membrane surface, as identified by Western blot analysis. We purified both proteins from human platelet membranes using DEAE-Sepharose chromatography followed by mAb F11 affinity chromatography. When added to platelet-rich plasma, the purified proteins dose-dependently inhibited mAb F11-induced platelet aggregation. The purified protein preparation also competitively inhibited the binding of 125I-labelled mAb F11 to intact platelets. The N-terminal 26 amino acid sequences of both the 32 and 35 kDa proteins were identical and contained a single unblocked serine in the N-terminal position. When digested with N-glycanase, the 32 and 35 kDa proteins were converted into a single approximately 29 kDa protein, indicating that these two proteins are derived from the same core protein but differ in their degree of glycosylation. Internal amino acid sequence analysis of the F11 antigen provided information concerning 68 amino acids and suggested two consensus phosphorylation sites for protein kinase C (PKC). The phosphorylation by PKC of the isolated F11 antigen was observed following stimulation by phorbol 12-myristate 13-acetate. Databank analysis of the N-terminal and internal amino acid sequences of the F11 antigen indicated that the N-terminal sequence exhibited the highest degree of similarity to the variable region of the alpha-chain of human T-cell receptors (TCR). In contrast, the F11 internal sequences did not exhibit any similarity to the TCR. Our results demonstrate that the F11 antigen is a novel platelet membrane surface glycoprotein which becomes cross-linked with the Fc gamma RII receptor when platelets are activated by the stimulatory mAb F11. These mechanisms may be relevant to the production of immune thrombocytopenia by platelet-activating antibodies.
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PMID:Mechanisms of platelet activation by a stimulatory antibody: cross-linking of a novel platelet receptor for monoclonal antibody F11 with the Fc gamma RII receptor. 764 39