Kinetic and Structural Analysis of Two Linkers in the Tautomerase Superfamily: Analysis and Implications
作者:Bert-Jan Baas、Brenda P. Medellin、Jake A. LeVieux、Kaci Erwin、Emily B. Lancaster、William H. Johnson、Tamer S. Kaoud、R. Yvette Moreno、Marieke de Ruijter、Patricia C. Babbitt、Yan Jessie Zhang、Christian P. Whitman
DOI:10.1021/acs.biochem.1c00220
日期:2021.6.8
The tautomerase superfamily (TSF) is a collection of enzymes and proteins that share a simple β–α–β structural scaffold. Most members are constructed from a single-core β–α–β motif or two consecutively fused β–α–β motifs in which the N-terminal proline (Pro-1) plays a key and unusual role as a catalytic residue. The cumulative evidence suggests that a gene fusion event took place in the evolution of the TSF followed by duplication (of the newly fused gene) to result in the diversification of activity that is seen today. Analysis of the sequence similarity network (SSN) for the TSF identified several linking proteins (“linkers”) whose similarity links subgroups of these contemporary proteins that might hold clues about structure–function relationship changes accompanying the emergence of new activities. A previously uncharacterized pair of linkers (designated N1 and N2) was identified in the SSN that connected the 4-oxalocrotonate tautomerase (4-OT) and cis-3-chloroacrylic acid dehalogenase (cis-CaaD) subgroups. N1, in the cis-CaaD subgroup, has the full complement of active site residues for cis-CaaD activity, whereas N2, in the 4-OT subgroup, lacks a key arginine (Arg-39) for canonical 4-OT activity. Kinetic characterization and nuclear magnetic resonance analysis show that N1 has activities observed for other characterized members of the cis-CaaD subgroup with varying degrees of efficiencies. N2 is a modest 4-OT but shows enhanced hydratase activity using allene and acetylene compounds, which might be due to the presence of Arg-8 along with Arg-11. Crystallographic analysis provides a structural context for these observations.
双烯酮异构酶超家族(TSF)是一组共享简单β–α–β结构支架的酶和蛋白质。大多数成员由单个核心β–α–β基序或两个连续融合的β–α–β基序构成,其中N-末端脯氨酸(Pro-1)作为催化残基发挥关键而独特的作用。累计证据表明,在TSF的进化过程中发生了基因融合事件,随后对新融合基因进行了复制,从而导致了今天所见的活性多样化。对TSF的序列相似性网络(SSN)分析识别出几种连接蛋白(“连接器”),它们的相似性将这些当代蛋白质的子群联系起来,这可能为新活性出现时伴随的结构–功能关系变化提供线索。在SSN中识别出一对先前未表征的连接器(指定为N1和N2),它们连接了4-草酰基氯烯烃异构酶(4-OT)和顺式-3-氯丙烯酸脱卤酶(cis-CaaD)子群。N1位于cis-CaaD子群中,具有顺式-CaaD活性所需的全面活性位点残基,而N2位于4-OT子群中,缺少用于典型4-OT活性的重要精氨酸(Arg-39)。动力学表征和核磁共振分析显示,N1的活性与cis-CaaD子群中的其他已表征成员相似,且效率各不相同。N2是一个适度的4-OT,但在使用炔烃和乙炔化合物时显示出增强的水合酶活性,这可能与Arg-8和Arg-11的存在有关。晶体学分析为这些观察提供了结构背景。