Mutational dynamics of murine angiogenin duplicates

Abstract

BackgroundAngiogenin (Ang) is a protein involved in angiogenesis by inducing the formation of blood vessels. The biomedical importance of this protein has come from findings linking mutations in Ang to cancer progression and neurodegenerative diseases. These findings highlight the evolutionary constrain on Ang amino acid sequence. However, previous studies comparing human Angiogenin with homologs from other phylogenetically related organisms have led to the conclusion that Ang presents a striking variability. Whether this variability has an adaptive value per se remains elusive. Understanding why many functional Ang paralogs have been preserved in mouse and rat and identifying functional divergence mutations at these copies may explain the relationship between mutations and function. In spite of the importance of testing this hypothesis from the evolutionarily and biomedical perspectives, this remains yet unaccomplished. Here we test the main mutational dynamics driving the evolution and function of Ang paralogs in mammals.ResultsWe analysed the phylogenetic asymmetries between the different Ang gene copies in mouse and rat in the context of vertebrate Ang phylogeny. This analysis shows strong evidence in support of accelerated evolution in some Ang murine copies (mAng). This acceleration is not due to non-functionalisation because constraints on amino acid replacements remain strong. We identify many of the amino acid sites involved in signal localization and nucleotide binding by Ang to have evolved under diversifying selection. Compensatory effects of many of the mutations at these paralogs and their key structural location in or nearby important functional regions support a possible functional shift (functional divergence) in many Ang copies. Similarities between 3D-structural models for mAng copies suggest that their divergence is mainly functional.ConclusionsWe identify the main evolutionary dynamics shaping the variability of Angiogenin in vertebrates and highlight the plasticity of this protein after gene duplication. Our results suggest functional divergence among mAng paralogs. This puts forward mAng as a good system candidate for testing functional plasticity of such an important protein while stresses caution when using mouse as a model to infer the consequences of mutations in the single Ang copy of humans.

Crystal structures of murine angiogenin‐2 and ‐3 – probing ‘structure – function’ relationships amongst angiogenin homologues

“…These Ang structures have enabled us to carry out a more rigorous and authentic structure‐based analysis than that presented by Codoñer et al . , which was based on 3D structural models for the different murine angiogenins. The most important difference between our analysis, based on our experimentally observed data, and theirs is the configuration of the catalytic centre in mAng‐2.…”

“…Codoñer et al . suggest that a possible reason for the angiogenic incompetence of mAng‐2 (unlike mAng) is a more effective blockage of its active site. In our structures, however, we observe that mAng‐2 has a more open active site than hAng or mAng.…”

“…Even though these structures are broadly similar to the previously elucidated 3D structures of hAng, mAng and mAng-4, there are important albeit subtle differences amongst these proteins that have been highlighted in the course of the present study. These Ang structures have enabled us to carry out a more rigorous and authentic structurebased analysis than that presented by Codoñer et al [32], which was based on 3D structural models for the different murine angiogenins. The most important difference between our analysis, based on our experimentally observed data, and theirs is the configuration of the catalytic centre in mAng-2.…”

“…The most important difference between our analysis, based on our experimentally observed data, and theirs is the configuration of the catalytic centre in mAng-2. Codoñer et al [32] suggest that a possible reason for the angiogenic incompetence of mAng-2 (unlike mAng) is a more effective blockage of its active site. In our structures, however, we observe that mAng-2 has a more open active site than hAng or mAng.…”

“…Evolutionary studies by Codoñer et al . suggest that there is functional divergence amongst the mAng paralogues even though the 3D models for the proteins are extremely similar. Experiments have shown that mAng, mAng‐3 and mAng‐4 have angiogenic activities comparable to that of hAng, whereas mAng‐2 is not angiogenic .…”