The epidermal growth factor precursor. A calcium-binding, beta-hydroxyasparagine containing modular protein present on the surface of platelets.
Various human body fluids and secretions contain a soluble form of the epidermal growth factor (EGF) precursor. The EGF precursor molecule contains eight EGF modules in addition to EGF itself. Using monoclonal antibodies specific for the EGF modules 7 and 8, we have purified the soluble form of the EGF precursor from human urine to homogeneity. The protein was shown to have a molecular mass of about 160 kDa and the N-terminal sequence SAPNHWSXPE. EGF modules 2, 7 and 8 of the precursor have the consensus sequence for post-translational beta-hydroxylation of Asp/Asn residues. We identified the presence of erythro-beta-hydroxy-aspartic acid (Hya) in acid hydrolysates of the EGF precursor (2.4 M.M protein-1). As the DNA sequence encodes Asn in the corresponding position, the Hya represents erythro-beta-hydroxyasparagine (Hyn). The Hyn-containing modules have a consensus calcium-binding motif immediately N-terminal of the first Cys residue. The synthetic EGF module 2 (residues 356-395) of the EGF precursor was found to bind calcium with low affinity, Kd approximately 3.5 mM, i.e. similar to the affinity of other isolated calcium-binding EGF modules. EGF module 7, when part of the intact protein, was found to bind Ca2+ with a Kd approximately 0.2 microM, i.e. approximately 10(4)-fold higher than that of isolated EGF modules presumably due to the influence of neighboring modules. We have detected EGF precursor in platelet-rich plasma and demonstrated it to be associated to platelets. The platelets were found to have 30-160 EGF molecules each.
Valcarce
C
C
Department of Clinical Chemistry, University of Lund, University Hospital, Malmö, Sweden.
Björk
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I
Stenflo
J
J
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D001216:Asparagine / Q000031:analogs & derivatives / Q000032:analysis; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000097:blood / Q000737:chemistry* / Q000652:urine; D004815:Epidermal Growth Factor / Q000737:chemistry*; D005260:Female; D005453:Fluorescence; D006801:Humans; D006900:Hydroxylation; D008297:Male; D008969:Molecular Sequence Data; D017510:Protein Folding; D011498:Protein Precursors / Q000097:blood / Q000737:chemistry* / Q000652:urine; D011499:Protein Processing, Post-Translational
D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; D011498:Protein Precursors; C050931:3-hydroxyasparagine; D004815:Epidermal Growth Factor; D001216:Asparagine; D002118:Calcium