Molecular Identification of a Unique Heparin Binding Motif Derived from Human RNase3

Human ribonuclease A (hRNaseA) super family members have similar biological functions such as catalytic activities against specific RNA substrates. However, these enzymes with high sequence similarity may exhibit divergent physiological functions other than RNase activity, for example, angio genesis and innate immunity. In our investigation, a novel heparin-binding motif (HBM), RWRCK, identified from hRNase3 contributed to specific protein-heparin/heparan sulfate (HS) interaction. Based on this core HBM sequence, a 10-amino acid heparin binding peptide (HBP_RNase3), NYRWRCKNQN, has been designed and characterized. Employing Clustal W2 and Uniprot Blastn program, such HBP pattern is found to be conserved in human and higher primates. Multiple sequence alignment of 13 members of human RNase A family reveals that HBP regions in hRNase2 and hRNase8 share 80% and 50% sequence identity to HBP_RNase3, but the corresponding sequences of Gorilla and Pan troglodytes RNase3 are 100% identical, strongly suggesting that HBP_RNase3 is conserved in higher primates along with species evolution. Interestingly, the putative HBP_RNase2, NYQRRCKNQN, shows much lower heparin binding activity than HBP_RNase3. In summary, HBP_RNase3 is not a conserved motif in RNaseA superfamily, but it is a unique motif presenting in higher primates to play a crucial role in molecular interaction to heparin and HS.