Conformational Transition and Energy Landscape of ErbB4 Activated by Neuregulin1β: One Microsecond Molecular Dynamics Simulations Yun Du, Huaiyu Yang,* Yechun Xu, Xiaohui Cang, Cheng Luo, Yanyan Mao, Yuanyuan Wang, Guangrong Qin, Xiaomin Luo, and Hualiang Jiang* Drug Discovery and Design Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China * S Supporting Information ABSTRACT: ErbB4, a receptor tyrosine kinase of the ErbB family, plays crucial roles in cell growth and differentiation, especially in the development of the heart and nervous system. Ligand binding to its extracellular region could modulate the activation process. To under- stand the mechanism of ErbB4 activation induced by ligand binding, we performed one microsecond molecular dynamics (MD) simulations on the ErbB4 extracellular region (ECR) with and without its endogenous ligand neuregulin1β (NRG1β). The conformational transition of the ECR-ErbB4/NRG1β complex from a tethered inactive conformation to an extended active-like form has been observed, while such large and function-related conformational change has not been seen in the simulation on the ECR-ErbB4, suggesting that ligand binding is indeed the active inducing force for the conformational transition and further dimerization. On the basis of MD simulations and principal component analysis, we constructed a rough energy landscape for the conformational transition of ECR-ErbB4/NRG1β complex, suggesting that the conformational change from the inactive state to active-like state involves a stable conformation. The energy barrier for the tether opening was estimated as ∼2.7 kcal/mol, which is very close to the experimental value (1-2 kcal/mol) reported for ErbB1. On the basis of the simulation results, an atomic mechanism for the ligand-induced activation of ErbB4 was postulated. The present MD simulations provide a new insight into the conformational changes underlying the activation of ErbB4. ■ INTRODUCTION The ErbB family receptor tyrosine kinases consist of four members, epidermal growth factor receptor (ErbB1/EGFR), ErbB2 (HER2), ErbB3 (HER3), and ErbB4(HER4), all of which play fundamental roles in regulating cell proliferation and differentiation. 1 Members of this family share a similar structural arrangement and activation mechanism. Each member consists of an extracellular region, a single trans- membrane-spanning region, a cytoplasmic tyrosine kinase domain, and a carboxyl terminal domain. 2 Ligand binding to the extracellular region promotes activation and dimerization of ErbB receptors, leading to activation of their intracellular parts and thereby further triggering downstream pathways such as those centered on MAPK or PI3K. 3 Because of their important biological and pharmacological functions, ErbBs have been extensively studied as drug targets. 4 ErbB4 is the most recently characterized member of the ErbB family and has been shown to be essential in the development of nervous and cardiovascular systems. 5-7 Loss of function of the ErbB4 gene has been implicated in the pathology of diseases such as schizophrenia 8-10 and heart failure. 11 However, the role of ErbB4 in oncogenesis is far from clear; whether it is a tumor suppressor 12-17 or an oncogene 18-23 is still under debate. As the initiation step of an entire signaling cascade, abnormal ErbB4/ligand interactions in the extracellular region may take crucial roles in these pathogenic mechanisms. Accordingly, it is of particular importance to investigate the dynamic properties of ErbB4 extracellular region and its ligand-binding properties. 24 The neuregulin (NRG) family growth factors are endoge- nous ligands of ErbB4. 25 As the best characterized member, NRG1 has different variants of EGF-like domains (α and β), which differ in affinity to ErbB4. Also, the isolated EGF-like domain has been demonstrated to be necessary and sufficient for NRG1 to bind to and activate ErbB4. 26 Accordingly, this peptide ligand, the EGF-like domain of NRG1, has been widely used for studying the activation of ErbB4. As limited structural information was obtained about ErbB4, 25 relevant data for other homologues in the ErbB family are helpful in understanding the activation of the ErbB4 extracellular region (ECR). This region is composed of four domains arranged as tandem repeats of a leucine-rich domain (domains I and III) and a cysteine-rich domain (domains II and IV). 25 The currently available crystal structures of the ECRs of ErbBs comprise four states, that is, “unliganded-inactive”, Received: December 22, 2011 Published: February 8, 2012 Article pubs.acs.org/JACS © 2012 American Chemical Society 6720 dx.doi.org/10.1021/ja211941d | J. Am. Chem. Soc. 2012, 134, 6720-6731