Osteogenic protein-1 (OP-1) expression and processing in Chinese hamster ovary cells: isolation of a soluble complex containing the mature and pro-domains of OP-1.

We have characterized the expression and processing of Osteogenic Protein-1 (hOP-1), a bone morphogenic protein of the TGF-beta family, in Chinese hamster ovary cells. The hOP-1 is initially synthesized as a monomeric 50 kDa pro-protein that is dimerized, glycosylated, and then proteolytically cleaved at the Arg-Xaa-Xaa-Arg maturation site in an acidic cellular compartment before secretion into the medium. Of the four potential N-linked glycosylation sites two are used, one in the mature domain and one in the pro-domain. Gel permeation chromatography of secreted hOP-1 in physiological buffers yields an apparent molecular weight of 110-120 k, indicating that after proteolytic processing the two pro-domains remain non-covalently associated with the disulfide linked mature dimer in a complex termed soluble hOP-1. Purified soluble hOP-1 is significantly more soluble in physiological buffers than the purified mature OP-1.