Pseudomonas exotoxin A-epidermal growth factor (EGF) mutant chimeric protein as an indicator for identifying amino acid residues important in EGF-receptor interaction

Modeling the epidermal growth factor -- epidermal growth factor receptor l2 domain interaction: implications for the ligand binding process

Signaling from the epidermal growth factor (EGF) receptor is triggered by the binding of ligands such as EGF or transforming growth factor alpha (TGF-alpha) and subsequent receptor dimerization. An understanding of these processes has been hindered by the lack of structural information about the ligand-bound, dimerized EGF receptor. Using an NMR-derived structure of EGF and a homology model of the major ligand binding domain of the EGF receptor and experimental data, we modeled the binding of EGF to this EGF receptor fragment. In this low resolution model of the complex, EGF sits across the second face of the EGF receptor L2 domain and EGF residues 10-16, 36-37, 40-47 bind to this face. The structural model is largely consistent with previously published NMR data describing the residues of TGF-alpha which interact strongly with the EGF receptor. Other EGF residues implicated in receptor binding are accounted by our proposal that the ligand binding is a two-step process with the EGF binding to at least one other site of the receptor. This three-dimensional model is expected to be useful in the design of ligand-based antagonists of the receptor.

Receptor recognition by histidine 16 of human epidermal growth factor via hydrogen-bond donor/acceptor interactions

Human epidermal growth factor (hEGF) and human transforming growth factor alpha (hTGFalpha) are prototypical of structurally related polypeptide mitogens which interact with the epidermal growth factor receptor (EGFR). Several determinants of receptor recognition that specify function have been proposed on the basis of structural criteria. This study evaluates the role of one such candidate, H16 of hEGF, by site-specific mutagenesis. When assayed for receptor tyrosine kinase stimulation using (Glu4,Tyr1)n as the exogenous substrate in vitro, the relative agonist activities of position 16 mutants range from 14-263% of wild-type hEGF. The rank order of potency was found to correlate with the relative receptor binding affinities of the mutants, which range from 7-272% of wild-type, as determined by radioreceptor competition assays. The mitogenic activity of the H16 mutants is similar to that of wild-type hEGF as determined by clonogenic assays using rat tracheal epithelial cells. While the colony forming efficiencies do not reflect significant differences in growth rate or survival characteristics in the presence of the hEGF variants, it is reduced to 1.6% in control cultures which lack EGF in the medium. The results show that H16 of hEGF, although not essential for mitogenic activity, optimizes receptor recognition by hydrogen-bond donor/acceptor interactions and may share this feature with H18 of hTGFalpha.

Structure-function relationships for the EGF/TGF-alpha family of mitogens

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) are ligands for the EGF-receptor and act as mitogens for a variety of tissues. TGF-alpha, in particular, has been implicated as an autocrine growth factor for several cancer cell lines. Over the last 10 years many groups have examined the structure-function relationships in EGF/TGF-alpha in attempts to develop antagonists or agonists. In this review the results of these studies are summarised and related to the three-dimensional structure of EGF/TGF-alpha. The difficulties associated with the purification and characterisation of analogues of EGF/TGF-alpha and with the biological assays are discussed. It is clear that these difficulties have, in some cases, led to apparently contradicting results. The available binding data indicate that the receptor interaction surface for EGF/TGF-alpha might encompass one complete side of the molecule with a few strong binding determinants, in particular Arg41 and Leu47. The arginine at position 41 is the most critical residue and its full hydrogen-bonding capacity is needed for strong binding of EGF/TGF-alpha to the EGF-receptor. As this side of the molecule consists of residues from both the N- and C-terminal domain, it seems unlikely that agonists or antagonists can be developed on the basis of short peptides taken from the primary sequence. This concept is supported by the available binding and activity data.

Recent advances in heterologous gene expression in Escherichia coli

Recent advances in protein expression in E. coli have focused primarily on the enhancement of protein quality. Problems in mRNA translation such as inefficient initiation, mistranslation, frame-shifting and frame-hopping can often be addressed by altering heterologous gene-coding sequences. Fusion technology can also be used to address problems in translational initiation, the authenticity of amino-terminal amino acids, in vivo protein activity and protein purification. Accessory molecules, such as chaperones, are increasingly used to enhance protein quality in vivo and in vitro. E. coli has recently gained wide use as a host both for the engineering of proteins with altered activities and for the creation of multi-functional hybrids.