Copper binding to naturally occurring, lactam form of angiogenin differs from that to recombinant protein, affecting their activityElectronic supplementary information (ESI) available: Peptide synthesis and purification; potentiometric and UV-vis characterization of peptide-copper(ii) complex species; ESI-MS measurements; and NMR tables. See DOI: 10.1039/c5mt00216h

Angiogenin is a member of the ribonuclease family and a normal constituent of human plasma. It is one of the most potent angiogenic factors known and is overexpressed in different types of cancers. Copper is also an essential cofactor in angiogenesis and, during this process, it is mobilized from inside to outside of the cell. To date, contrasting results have been reported about copper( ii ) influencing angiogenin activity. However, in these studies, the recombinant form of the protein was used. Unlike recombinant angiogenin, that contains an extra methionine with a free terminal amino group, the naturally occurring protein present in human plasma starts with a glutamine residue that spontaneously cyclizes to pyroglutamate, a lactam derivative. Herein, we report spectroscopic evidence indicating that copper( ii ) experiences different coordination environments in the two protein isoforms, and affects their RNase and angiogenic activity differently. These results show how relatively small differences between recombinant and wild type proteins can result in markedly different behaviours. RNase catalytic site His-114 is the Cu 2+ anchoring site in effective angiogenin protein, whereas in recombinant form is the amino terminus.