Latent high molecular weight complex of transforming growth factor beta 1. Purification from human platelets and structural characterization.
Human transforming growth factor beta 1 (TGF-beta 1) was purified as a latent high Mr complex from human platelets by a six-step procedure. Analysis by sodium dodecyl sulfate (SDS)-gel electrophoresis under reducing conditions revealed that the complex was composed of at least three components with apparent Mr values of 13,000, 40,000, and 125,000-160,000. The 13-kDa subunit was part of a disulfide-bonded dimer and was identified by amino acid sequencing as TGF-beta 1. The 40-kDa subunit was identified as the amino-terminal part of the TGF-beta 1 precursor lacking the hydrophobic signal sequence. Partial sequencing of the 125-160-kDa protein revealed that it is distinct from known proteins. The 40-kDa and the 125-160-kDa subunits are linked by disulfide bonds, forming a complex with an apparent Mr of 210,000 on SDS gels under nonreducing conditions. Experiments with partial reduction revealed that each complex contains two 40-kDa components linked by disulfide bonds; in addition, the dimer is disulfide-linked to one 125-160-kDa binding protein. TGF-beta 1 binds noncovalently to the 210-kDa complex, and in bound form, TGF-beta 1 is inactive. Incubations of the latent form of TGF-beta 1 at extreme pH values, in 0.02% SDS or in 8 M urea, lead to activation of TGF-beta 1, whereas the complex was resistant to treatment with 5 M NaCl or heat (3 min at 95 degrees C).
Miyazono
K
K
Ludwig Institute for Cancer Research, Uppsala, Sweden.
Hellman
U
U
Wernstedt
C
C
Heldin
C H
CH
D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000032:analysis*; D002850:Chromatography, Gel; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000097:blood / Q000302:isolation & purification*; D015291:Transforming Growth Factors
D010455:Peptides; D015291:Transforming Growth Factors