Peptidyl Prolyl Isomerases (PPIases) accelerate cis–trans isomerization of prolyl peptide bonds. In rice, the PPIase LRT2 is essential for lateral root initiation. LRT2 displays in vitro isomerization of a highly conserved W–P peptide bond (¹⁰⁴W–P¹⁰⁵) in the natural substrate OsIAA11. OsIAA11 is a transcription repressor that, in response to the plant hormone auxin, is targeted to ubiquitin-mediated proteasomal degradation via specific recognition of the cis isomer of its ¹⁰⁴W–P¹⁰⁵ peptide bond. OsIAA11 controls transcription of specific genes, including its own, that are required for lateral root development. This auxin-responsive negative feedback circuit governs patterning and development of lateral roots along the primary root. The ability to tune LRT2 activity via mutagenesis is crucial for understanding and modeling the role of this bimodal switch in the auxin circuit and lateral root development. We present characterization of the thermal stability and isomerization rates of several LRT2 mutants acting on the OsIAA11 substrate. The thermally stable mutants display activities lower than that of wild-type (WT) LRT2. These include binding diminished but catalytically active P125K, binding incompetent W128A, and binding capable but catalytically incompetent H133Q mutations. Additionally, LRT2 homologs hCypA from human, TaCypA from Triticum aestivum (wheat) and PPIB from E. coli were shown to have 110, 50 and 60% of WT LRT2 activity on the OsIAA11 substrate. These studies identify several thermally stable LRT2 mutants with altered activities that will be useful for establishing relationships between cis–trans isomerization, auxin circuit dynamics, and lateral root development in rice.

肽脯氨酰异构酶（PPIases）加快顺-反式的脯氨酰肽键异构化。在水稻中，PPIase LRT2对于侧向生根至关重要。LRT2在天然底物OsIAA11中显示了高度保守的W-P肽键（¹⁰⁴ W-P ¹⁰⁵）的体外异构化。OsIAA11是一种转录阻遏物，针对植物激素生长素，通过特异性识别其¹⁰⁴ W-P ¹⁰⁵的顺式异构体而靶向于泛素介导的蛋白酶体降解肽键。OsIAA11控制着侧根发育所需的特定基因（包括其自身）的转录。该生长素响应性负反馈电路控制着沿初生根的侧根的构图和发育。通过诱变调节LRT2活性的能力对于理解和建模这种双峰开关在生长素回路和侧根发育中的作用至关重要。我们介绍了对OsIAA11底物起作用的几个LRT2突变体的热稳定性和异构化率的表征。热稳定突变体显示的活性低于野生型（WT）LRT2。这些包括结合减少但具有催化活性的P125K，结合能力不强的W128A和结合能力但催化能力不强的H133Q突变。此外，LRT2与人类hCypA同源，普通小麦（小麦），并从PPIB大肠杆菌显示出具有WT LRT2活性的110，50和60％的OsIAA11基板上。这些研究确定了几种具有改变活性的热稳定LRT2突变体，这些突变体对于建立水稻的顺式-反式异构化，生长素回路动力学和侧根发育之间的关系将是有用的。