Investigation of beta-alanine aminotransferase at the crossroad of pyrimidine, polyamine, coenzyme A and branched chain amino acid metabolism

植物能够降解它们所含的核酸和核苷酸，以保持新陈代谢的平衡，并获得营养和能量。嘧啶核苷酸（尿嘧啶和胸腺嘧啶）的环在三个反应中被还原和打开，由尿嘧啶生成β -丙氨酸（BA）和由胸腺嘧啶生成β -氨基异丁酸（BAIBA）。这些产物如何进一步降解以及嘧啶环降解如何与中枢代谢联系尚不清楚。BA不仅可以流入进一步降解，而且是胞质溶胶中辅酶A合成的必需前体。然而，由于嘧啶环降解突变体在CoA生物合成方面没有缺陷，因此植物代谢仍然必须能够通过其他方式提供BA。这可能涉及多胺的降解，发生在细胞质和过氧化物酶体中。我们发现了以丙酮酸为受体将BA和BAIBA转氨酶转化为相应的醛和丙氨酸- β -丙氨酸转氨酶（BAAT）的酶。BAAT位于过氧化物酶体和线粒体中。基于我们的初步数据、文献数据和可行性假设，我们建立了BA和BAIBA代谢的工作模型，该模型假设BA和BAIBA可以在线粒体中被支链氨基酸降解酶降解为乙酰辅酶a。通过使用同位素标记技术对多种嘧啶和多胺代谢突变体的代谢物进行量化，我们的目标是将我们的工作模型转化为实验证明的代谢模型。这将整合嘧啶和多胺分解代谢以及辅酶a合成和部分支链氨基酸降解途径，考虑到细胞质，线粒体和过氧化物酶体中的反应。包括BAAT在内的几种以前未知的生理作用的酶将被研究，理想情况下，它们在代谢中的功能将被阐明。对于BAAT，我们还将进行晶体结构分析。此外，还将阐明辅酶a合成的BA来源，并追踪baat介导的转氨化产生的氮的途径。此外，我们还将研究在短期碳限制下，嘧啶是否会被更强地降解，转录数据表明这一点。因此，嘧啶环降解（可能还有多胺降解）可能有助于在碳饥饿期间短期提供乙酰辅酶a。通过基因组测序，我们已经知道了许多植物的基因组，但许多基因在代谢中的功能和相互关系仍不清楚。这项研究将有助于阐明一些基因的功能，并将在许多方面扩大对植物代谢的认识。

Plants are able to degrade nucleic acids and the nucleotides they contain to keep metabolism in balance and to obtain nutrients and energy. The ring of pyrimidine nucleotides (uracil and thymine) is reduced and opened in three reactions, forming beta-alanine (BA) from uracil and beta-aminoisobutyrate (BAIBA) from thymine. How these products are further degraded and how pyrimidine ring degradation is linked to central metabolism is as yet unknown. BA can not only flow into further degradation, but is also an essential precursor for the synthesis of coenzyme A in the cytosol. However, since pyrimidine ring degradation mutants do not have a defect in CoA biosynthesis, plant metabolism must still be able to provide BA by other means. This may involve the degradation of polyamines, which occurs in the cytosol and peroxisomes. We have discovered the enzyme that metabolizes BA and BAIBA by transamination with pyruvate as acceptor to the corresponding aldehydes and to alanine - beta-alanine aminotransferase (BAAT). BAAT is located in peroxisomes and mitochondria. Based on our preliminary data, literature data, and plausibility assumptions, we developed a working model of the metabolism surrounding BA and BAIBA, which postulates inter alia, that BA and BAIBA can be degraded in the mitochondria to acetyl-CoA by the enzymes of branched-chain amino acid degradation. By quantifying metabolites using also isotope labeling techniques in a broad variety of mutants of pyrimidine and polyamine metabolism, we aim to convert our working model into an experimentally proven metabolic model. This will integrate pyrimidine and polyamine catabolism as well as CoA synthesis and parts of the degradation pathway of branched-chain amino acids, considering reactions in the cytosol, mitochondria and peroxisomes. Several enzymes, including BAAT, with previously unknown physiological roles will be investigated and ideally their function in metabolism will be elucidated. For BAAT, we will also perform crystal structure analysis. In addition, BA sources for CoA synthesis will be elucidated and the pathway of nitrogen derived from BAAT-mediated transamination will be traced. Furthermore, it will be investigated whether pyrimidines are more strongly degraded under short-term carbon limitation, which transcriptional data suggest. Thus, pyrimidine ring degradation (and possibly also polyamine degradation) could contribute to the short-term provision of acetyl-CoA during carbon starvation. Through genome sequencing, the genomes of many plants are now known, but many of the gene functions and interconnections in metabolism are still unclear. This research will contribute to the elucidation of several gene functions and will expand the understanding of plant metabolism in many ways.