Insight into the Binding Properties of MEKK3 PB1 to MEK5 PB1 from Its Solution Structure

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• 作者：Qi Hu ; Weiqun Shen ; Hongda Huang ; Jiangxin Liu ; Jiahai Zhang ; Xiaojuan Huang ; Jihui Wu ; Yunyu Shi
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：November 27, 2007
• 年：2007
• 卷：46
• 期：47
• 页码：13478 - 13489
• 全文大小：707K
• 年卷期：v.46,no.47(November 27, 2007)
• ISSN：1520-4995

文摘

MEKK3 is a mitogen-activated protein kinase kinase kinase that participates in various signalingpathways. One of its functions is to activate the ERK5 signal pathway by phosphorylating and activatingMEK5. MEKK3 and MEK5 each harbors a PB1 domain in the N-terminus, and they form a heterodimervia PB1-PB1 domain interaction that was reported to be indispensable to the activation of MEK5. UsingNMR spectroscopy, we show here that a prolyl isomerization of the Gln38-Pro39 bond is present inMEKK3 PB1, which is the first case of structural heterogeneity within PB1 domains. We have solved thesolution structures of both isomers and found a major difference between them in the Pro39 region. ResiduesGly37-Leu40 form a type VIb -turn in the cis conformation, whereas no obvious character of -turnwas observed in the trans conformation. Backbone dynamics studies have unraveled internal motions inthe 3/4-turn on a microsecond-millisecond time scale. Further investigation of its binding propertieswith MEK5 PB1 has demonstrated that MEKK3 PB1 binds MEK5 PB1 tightly with a K_d of about 10^-8M. Mutagenesis analysis revealed that residues in the basic cluster of MEKK3 PB1 contributes differentlyto the PB1-PB1 interaction. Residues Lys 7 and Arg 5 play important roles in the interaction with MEK5PB1. Taken together, this study provides new insights into structural details of MEKK3 PB1 and itsbinding properties with MEK5 PB1.