近日,，國際著名雜志《生物化學(xué)雜志》（Journal of Biological Chemistry,，JBC）在線刊登了中科院上海生科院營養(yǎng)所向嵩研究組的最新研究成果“Crystal structure of ureacarboxylase provides insights into the carboxyltransfer reaction，”,。該研究解析了尿素羧化酶(urea carboxylase,， UC）的三維結(jié)構(gòu)，揭示了其CarboxylTransferase（CT）結(jié)構(gòu)域催化反應(yīng)的機制,。
UC屬于依賴生物素的羧化酶家族,，該家族成員能羧化形式多樣的底物分子，在多條代謝途徑中發(fā)揮重要功能,。UC分布于多種微生物中,，它催化的由尿素生成脲(allophanate)的轉(zhuǎn)化反應(yīng)是這些微生物獲得氮元素的必需環(huán)節(jié)，氮元素在生物圈的循環(huán)中發(fā)揮重要功能,。向嵩研究員指導(dǎo)的博士研究生樊晨等利用結(jié)晶學(xué)的方法解析了UC的晶體結(jié)構(gòu),，捕捉到其CT結(jié)構(gòu)域催化反應(yīng)的一個中間態(tài)，并結(jié)合結(jié)構(gòu)信息指導(dǎo)的功能實驗結(jié)果,，揭示了CT結(jié)構(gòu)域催化反應(yīng)的機制,。另外，分析表明UC的CT結(jié)構(gòu)與其它依賴生物素的羧化酶有相似的地方,，因此對UC結(jié)構(gòu)和功能的了解也有助于理解依賴生物素羧化酶家族其它成員的催化機理,。該課題獲得國家科技部和中國科學(xué)院的經(jīng)費資助。（生物谷Bioon.com）
doi:10.1074/jbc.M111.319475
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Crystal structure of urea carboxylase provides insights into the carboxyltransfer reaction
Chen Fan1, Chi-Yuan Chou2, Liang Tong3 and Song Xiang1,*
Urea carboxylase (UC) is conserved in many bacteria, algae and fungi, and catalyzes the conversion of urea to allophanate, an essential step in the utilization of urea as a nitrogen source in these organisms. UC belongs to the biotin-dependent carboxylase superfamily, and shares the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains with these other enzymes, but its carboxyltransferase (CT) domain is distinct. Currently there is no information on the molecular basis of catalysis by UC. We report here crystal structure of the Kluyveromyces lactis UC and biochemical studies to assess the structural information. Structural and sequence analyses indicate the CT domain of UC belongs to a large family of proteins with diverse functions, including the Bacillus subtilis KipA-KipI complex, which has important functions in sporulation regulation. A structure of the KipA-KipI complex is not currently available, and our structure provides a framework to understand the function of this complex. Most interestingly, in the structure the CT domain interacts with the BCCP domain, with biotin and a urea molecule bound at its active site. This structural information and our follow-up biochemical experiments provided molecular insights into the UC carboxyltransfer reaction. Several structural elements important for the UC carboxyltransfer reaction are found in other biotin-dependent carboxylases and might be conserved within this family, and our data could shed light on the mechanism of these enzymes' catalysis.
