Lactoferrin contains structural motifs of ribonuclease

A high molecular weight ribonuclease isolated from human milk (hmRNAase) shares identical immunological, physical, structural features and considerable sequence homology with human lactoferrin; and it has been demonstrated to be an isoform of lactoferrin. We have analyzed the sequence data of lactoferrin looking for the existence of specific features corresponding to the consensus sequence of pyrimidine-specific ribonucleases. The analysis was done by comparing sequence features with respect to elements which are, in principle, responsible for RNAase activity. This revealed the existence of a ribonuclease-signature pattern in lactoferrin. Further analysis of X-ray data together with molecular modeling studies have revealed close similarities between the spatial geometry of the constituent groups of the active site of pyrimidine-specific ribonucleases and the corresponding groups comprising the potential active site of lactoferrin. Our results provide the strong structural basis for the existence of ribonuclease activity in lactoferrin.