Disclosed are biologically active protein conjugates that comprise a biologically active polypeptide coupled via a peptide bond to a polypeptide comprising from 2 to about 500 units of a repeating peptide motif, wherein the biologically active protein conjugate exhibits a modified plasma half-life compared to the intrinsic half-life of the unconjugated biologically active polypeptide or protein. Also disclosed are methods of making and using the conjugated proteins, as well as methods for determining whether a given conjugate exhibits a modified half life relative to the intrinsic half life of the unconjugated polypeptide.