Proteins consisting of two PDGF-D polypeptide chains, polynucleotides
encoding the polypeptides, and materials and methods for making the
proteins are disclosed. Each of the polypeptide chains consists of, from
amino terminus to carboxyl terminus, the following operably linked
segments: P1-P2-h-C.sub.H2-C.sub.H3; P1-P2-C.sub.H2-C.sub.H3;
h-C.sub.H2-C.sub.H3-P2-P1; or C.sub.H2-C.sub.H3-P2-P1. Within these
polypeptide chains, P1 is a first polypeptide segment as shown in SEQ ID
NO:2 or SEQ ID NO:4 from amino acid x to amino acid y, wherein x is an
integer from 246 to 258, inclusive, and y is an integer from 365 370,
inclusive; P2 is a second polypeptide segment consisting of from 4 to 20
amino acid residues; h is an immunoglobulin hinge region or portion
thereof; and C.sub.H2 and C.sub.H3 are C.sub.H2 and C.sub.H3 domains of
an immunoglobulin heavy chain, respectively. Within the protein, the two
polypeptide chains are joined by one or more disulfide bonds, each of the
chains is optionally glycosylated, and the protein binds to and activates
cell-surface PDGF receptors.