Latent high molecular weight complex of transforming growth factor. beta. 1

Human transforming growth factor ..beta..1 (TGF-..beta..1) was purified as a latent high M/sub r/ 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 M/sub r/ 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 M/sub r/ 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 resistantmore » to treatment with 5 M NaCl or heat (3 min at 95/sup 0/C).« less