RESUMO
The epidermal growth factor receptor (EGFR) family is an important class of receptor tyrosine kinases, mediating a variety of cellular responses in normal biological processes and in pathological states of multicellular organisms. Different modes of dimerization of the human EGFR transmembrane domain (TMD) in different membrane mimetics recently prompted us to propose a novel signal transduction mechanism based on protein-lipid interaction. However, the experimental evidence for it was originally obtained with slightly different TMD fragments used in the two different mimetics, compromising the validity of the comparison. To eliminate ambiguity, we determined the nuclear magnetic resonance (NMR) structure of the bicelle-incorporated dimer of the EGFR TMD fragment identical to the one previously used in micelles. The NMR results augmented by molecular dynamics simulations confirm the mutual influence of the TMD and lipid environment, as is required for the proposed lipid-mediated activation mechanism. They also reveal the possible functional relevance of a subtle interplay between the concurrent processes in the lipid and protein during signal transduction.
Assuntos
Membrana Celular/química , Receptores ErbB/química , Bicamadas Lipídicas/química , Peptídeos/química , Transdução de Sinais/genética , Sequência de Aminoácidos , Membrana Celular/metabolismo , Clonagem Molecular , Dimiristoilfosfatidilcolina/química , Dimiristoilfosfatidilcolina/metabolismo , Receptores ErbB/genética , Receptores ErbB/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Humanos , Interações Hidrofóbicas e Hidrofílicas , Bicamadas Lipídicas/metabolismo , Micelas , Simulação de Dinâmica Molecular , Peptídeos/genética , Peptídeos/metabolismo , Éteres Fosfolipídicos/química , Éteres Fosfolipídicos/metabolismo , Domínios Proteicos , Multimerização Proteica , Estrutura Secundária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismoRESUMO
Receptor tyrosine kinases of the human epidermal growth factor receptor (HER or ErbB) family transduce biochemical signals across plasma membrane, playing a significant role in vital cellular processes and in various cancers. Inactive HER/ErbB receptors exist in equilibrium between the monomeric and unspecified pre-dimerized states. After ligand binding, the receptors are involved in strong lateral dimerization with proper assembly of their extracellular ligand-binding, single-span transmembrane, and cytoplasmic kinase domains. The dimeric conformation of the HER2 transmembrane domain that is believed to support the cytoplasmic kinase domain configuration corresponding to the receptor active state was previously described in lipid bicelles. Here we used high-resolution NMR spectroscopy in another membrane-mimicking micellar environment and identified an alternative HER2 transmembrane domain dimerization coupled with self-association of membrane-embedded cytoplasmic juxtamembrane region. Such a dimerization mode appears to be capable of effectively inhibiting the receptor kinase activity. This finding refines the molecular mechanism regarding the signal propagation steps from the extracellular to cytoplasmic domains of HER/ErbB receptors.