Molecular Evolutionary Analyses On Alanine-glyoxylate Aminotransferase Gene In Mammals

Alanine: glyoxylate aminotransferase I [AGT] catalyzes the intermediate metabolite glyoxylic acid to glycine,an effective detoxification reaction.The enzyme in carnivorous animals catalyze the hydroxyproline to glyoxylic acid in hepatocyte mitochondria.The herbivorous species converts glycolic acid into glyoxylic acid in hepatocyte peroxidase.Although glyoxylic acid itself is not necessarily harmful,it is easy to be oxidized to be oxalic acid,which will be accumulated in animal kidneys and eventually lead to the harmful kidney stones.In this study,we explore the molecular mechanism of mammalian feeding evolution by studying the relationship between mammalian alanine-glyoxylate aminotransferase and their feeding habits,the results of which can provide a theoretical basis for animal husbandry for different mammalian species.Here,we amplified a part of the mammalian alanine-glyoxylate aminotransferase gene sequence and found that the mitochondrial targeting function of the Marmota himalayana,Macropus rufus and Macropus rufogriseus was lost.At the same time,we analyzed the gene sequences obtained from the NCBI database.The alanine-glyoxylate aminotransferase subcellular targeting efficiency for each species was predicted using the Protein Subcellular Localization Prediction Tool(PSORT).It was found that there were up to 32 species of mitochondrial target sequence loss in herbivores,accounting for about 1/4 of the total number of herbivores;7 species of omnivorous animals;2 species of carnivorous animals.According to their diets,we divided the efficiency values into three groups:carnivorous,omnivorous,and herbivorous,and the values are significantly different(carnivores: 0.85±1.03,omnivores: 0.30±1.57,herbivores:-0.94±1.53).The results indicate that the gene is mainly expressed in mitochondria in carnivores,in both mitochondria and peroxisomes in omnivores,and in peroxisomes in herbivores.As a group of carnivorous mammals,cetaceans have a mitochondrial targeting efficiency of less than 0,but are higher than the other cetartiodactylan species.Because the diet of cetaceans have changed from herbivorous to carnivorous during their aquatic adaptation,the mitochondrial targeting efficiency is significantly increased.Analysis of the efficiency value and loss of function of the mitochondrial target sequence revealed that the subcellular targeting of mammalian alanine-glyoxylate aminotransferase is related to its diet.In this study,the alanine-glyoxylate aminotransferase gene of the red kangaroo was amplified and found to have a complete coding region,which can normally perform biological functions.According to the nucleotide and amino acid trees based on the gene,we found the alanine-glyoxylate aminotransferase gene was very conserved during mammalian evolution.In the selective pressure analyses,the results based on the branch-site models found positive selections in Yangochiroptera,Metatheria,Sciuridae and also the platypus.However,according to other tests,it was found that the alanine-glyoxylate aminotransferase gene has been very conservative during mammalian evolution and could be related to its critical function.The reason why the alanine-glyoxylate aminotransferase gene is conserved during mammalian evolution may be due to the detoxification effect of this gene,which plays a key role in the normal survival of organisms.