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Structure and dynamics of the epidermal growth factor receptor C-terminal phosphorylation domain

¹ Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242-1109, USA
² Laboratory for Fluorescence Dynamics, Department of Physics, University of Illinois, Urbana, Illinois 61801-3080, USA

(RECEIVED December 14, 2005; FINAL REVISION February 7, 2006; ACCEPTED February 7, 2006)

The C-terminal phosphorylation domain of the epidermal growth factor receptor is believed to regulate protein kinase activity as well as mediate the assembly of signal transduction complexes. The structure and dynamics of this proposed autoregulatory domain were examined by labeling the extreme C terminus of the EGFR intracellular domain (ICD) with an extrinsic fluorophore. Fluorescence anisotropy decay analysis of the nonphosphorylated EGFR-ICD yielded two rotational correlation times: a longer time, consistent with the global rotational motion of a 60- to 70-kDa protein with an elongated globular conformation, and a shorter time, presumably contributed by segmental motion near the fluorophore. A C-terminally truncated form of EGFR-ICD yielded a slow component consistent with the rotational motion of the 38-kDa kinase core. These findings suggested a structural arrangement of the EGFR-ICD in which the C-terminal phosphorylation domain interacts with the kinase core to move as an extended structure. A marked reduction in the larger correlation time of EGFR-ICD was observed upon its autophosphorylation. This dynamic component was faster than predicted for the globular motion of the 62-kDa EGFR-ICD, suggesting an increase in the mobility of the C-terminal domain and a likely displacement of this domain from the kinase core. The interaction between the SH2 domain of c-Src and the phosphorylated EGFR C-terminal domain was shown to impede its mobility. Circular dichroism spectroscopy indicated that the EGFR C-terminal domain possessed a significant level of secondary structure in the form of -helices and -sheets, with a marginal change in -sheet content occurring upon phosphorylation.

Keywords: protein tyrosine kinase; ErbB; HER; fluorescence anisotropy

Article published online ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.052045306.

Abbreviations: EGFR, epidermal growth factor receptor; SH2, Src homology-2; PTB, phosphotyrosine binding; PTK, protein tyrosine kinase; A-loop, activation loop; ICD, intracellular domain; CD, circular dichroism; CT, C-terminal truncation; CBD, chitin-binding domain; EDANS, 5-((2-aminoethyl)amino)naphthalene-1-sulfonic acid; CEDANS, cysteine- conjugated EDANS; EGFR-CT, C-terminal domain of EGFR; GST, glutathione-S-transferase; TNP-ATP, 2'(3')-O-(2,4,6-trinitrophenyl)-adenosine 5'-triphosphate.

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