The epidermal growth factor precursor

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‐traslational β‐hydroxylation of Asp/Asn residues. We identified the presence of erythro ‐β‐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 ‐β‐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, Κ d  ≈ 3.5 m m , 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 Ca 2+ with a K d  ≈ 0.2 µ m , i.e. ≈10 4 ‐fold higher than that of isolated EGF modules presumably due to the influence of neigboring 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.