Molecular Evolution Of Alanine:Glyoxylate Aminotransferase In Birds

Alanine:glyoxylate aminotransferase(also known as AGT)is an important hepatic enzyme that can transform cellular glyoxylate into glycine,preventing glyoxylate from being oxidized into oxalate,and also play an important role in providing energy to organisms through gluconeogenesis.Previous studies showed that AGT is located in mitochondria when its mitochondrial targeting sequence(MTS)can be translated to signal peptide,otherwise it is located in peroxisomes.Differential organelle's localizations of AGT are closely associated with diverse dietary habits.Generally,in carnivorous and herbivorous mammals,AGT is separately located in mitochondria and peroxisomes,while in omnivorous mammals,it can be located in both mitochondria and peroxisomes.The correct organelle's localization of AGT is essential to mammalian survival.For instance,the mistargeting event of AGT to mitochondria in humans would cause glyoxylate in peroxisomes unable to efficiently transform to glycine,and eventually glyoxylate is oxidized into harmful oxalate.Birds belong to the most species-rich group among tetrapod vertebrates and possess a high diversity in diets,serving as the ideal model to study the dietary adaptation.However,studies on the AGT organelle's localization are scarce.Here we explore the correlation between avian diets and AGT organelle's location,and the molecular evolution process of AGT in birds with diverse dietary habits.Finally,14 complete avian AGT genes were obtained through the BLAST approach based on 48 avian genomes and were synthesized and inserted into modified pEGFP-N3 vectors.Immunofluorescence assays were subsequently conducted,and a total of 11 species were successfully imaged.Images on avain AGT's immunofluorescence colocalization showed that birds with higher meat consumption tend to have a higher AGT's mitochondrial targeting efficiency than those with lower meat consumption.Meanwhile,the correlation analysis revealed that the AGT's mitochondrial targeting efficiency was positively correlated with the proportion of dietary meat.The evolutionary analysis revealed that the MTS evolved more rapidly than the mature region(AGT mature protein sequences after removing the MTS signal peptide),indicating the MTS under positive selection tends to obtain different mitchondrial targeting efficiencies in birds with different dietary types.Furthermore,positively selected sites were detected in both MTS and mature regions.Thus,our findings suggest that avian AGT genes may have undergone adaptive evolution in response to changes in diet.